Philosophy of Science. A Very Short Introduction

FREEW I LL Th o n r a rl 'l r r k FUNDAM I NTn L l 5 M MaliseRuthverr

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"? knowsthatsubjectssuchasphysics,chemistryandbiology constitutescience,while subjectssuchasart, music,and theolory ao ,ro,.gu, whenasphilosopherswe askrvhatscienceis, that is not thesortofanswerwewant.wearenotaskingforamerelistofthe activitiesthat areusuallycalled'science'.Rather,we areaskingwhat ",

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common feature all the;hings on that list share, i.e. what it is that makessornethinga science.understooclthis way,our question is notsotrivial.

Butyoumaystill rink theque6tionis rclativelystraightforward. Surclyscience isjusttheattemptto underutrn4e*pl.in,snd predictthe*orld w€lii€ in?This is certainlye r€rloncblearrswer. Brtisittheu'/rrolestory?Afilr all, thevirious rcligionsaboattempt to understandanderelatntheworld,but religionis not usually regarded as. branchof science. similaf,ly,o3tmlo8f.nd fortunetellintare attemptsto pr€dic{t}refuture,butmogtpeoplewouldnot de*ibelhese activitis 0i sciencr.or considerhistory.Historians try to understandandexplainwhathappened in the prst, but historyis usuillyclassiffed asan&rtssubjectnotascience subjec{Aswilh manyphilosophical questions. qu€gtion the \.'fi.t is scienc.e?'.tums out to betrickier $an it look! .t first sighL Manvpeoplebelieveth|t thedistinsuishinsfeatursofsci"''c'elie in I .

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the particular methods scientists use to investigate thr: world. This suggestionis quite plausible. For many sciencestlo employ distinctive methods of enquiry that are not found in non-scientific disciplines. An obvious example is the use of experiments,which historically marks a turning-point irr tlre development of modern science.Not all the sciencesare experimental though - astronomers obviously cannot tlo experiments on the heavens,but have to content thenrselveswith careful observation instead. The same is true of many social sciences.Another important feature of scienceis the construction of theories. Scientistsdo not simply record the results of experiment and observation in a log book - they usually want to explain those results in terms of a general theory. This is not always easyto do, but there have been some striking successes.One of the key problems in philosophy of scienceis to understand how o techniques such as experimentation, observation, ancl theoryE .g construction have enabled scientists to unravel so many of nature's Ji o secrets. c CI o

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Theoriginsof modernscience In today's schoolsand universities, scienceis taught in a largely ahistorical way. Textbookspresent the key ideas of a scientilic discipline in as convenient a form as possible,with little.mention of the lengthy and often tortuous historica-lprocessthat led to their discovery.As a pedagogicalstrategy,this makes good sense.But some appreciation of the history of scientific ideas is helpful for understand.ingthe issuesthat interest philosophers of science. Indeed as we shall seein Chapter 5, it has been argueclthat close attention to the history of scienceis indispensalrlefor cloing good philosophyofscience. The origins of modern scidncelie in a period of rapiclscientific development that occurred in Europe between the years l5OO and 175O,which we now refer to as the scientific revolution. Of course scientific investigations were pursued in ancient alrtl nredieval

times too - the scientific revolution did not come from nowhere. In theseearlier periods the dominant world-view was Aristotelianism, named after the ancient Greek philosopher Aristotle, who put forward detailed theories in physics,biology, astronomy, and cosmology.But Aristotle's ideas would seemvery strange to a modern scientist, as would his methods of enquiry. To pick just one example,he believed that all earthly bodies are composedofjust four elements: earth, fire, air, and water. This view is obviously at odds with what modern chemistrv tells us. The first crucial step in the development of the modern scientific world-view was the Copernican revolution. In 1542 the Polish astronomer Nicolas Copernicus (t+7s-$+e) published a book attacking the geocentric model of the universe,which placed the stationary earth at the centre of the universe with the planets and the sun in orbit around it. Geocentric astronomy, also known as E Ptolemaic astronomy afterthe ancient Greek astronomer Ptolemy, i lay at the heart of the Aristotelian world-view, and had gone largely unchallengedfor 1,8oo years. But Copernicus suggestedan 9 q alternative: the sunwas the fixed centre of the universe, and the planets,including the earth, were in orbit around the sun (Figure r). On this heliocentric model the earth is regarded asjust another planet, and so losesthe unique status that tradition had accorded it. Copernicus'theory initially met with much resistance,not least from the Catholic Church who regarded it as contravening the Scriptuies and in 1616banned books advocating the earth's motion. But within 1oo years Copernicanism had become established scientific orthodory.

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Copernicus' innovation did not merely lead to a better astronomy. Indirectly, it led to the development of modern physics,through the work of JohannesKepler (r5n-163o) and Galileo Galilei (15641642). Kepler discoveredthat the planets do not move in circular orbits around the sun, as Copernicus thought, but rather in ellipses. This was his crucial'first lad of planetary motion; his second and third laws specifuthe speedsat which the planets orbit the sun.

freely falling bodies will fall towards the earth at the salne rate, irrespectiveof their weight (Figure 2). (Of course in practiee, if you drop a feather and a cannon-ball from tlre same height the cannonball will land first, but Galileo argued that this is simply due to air resistance- in a vacuum, they would land together.) Furthermore, he argued that freely falling bodies accelerateuniformly, i.e. gain equal increments of speed in equal times; this is known as Galileo's law of free-fall. Galileo provided persuasivethough not totally conclusiveevidencefor this law, which formed the centrepieceof his theory of mechanics.

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Taken together, Kepler's laws provided a far superior planetary theory than had ever been advancedbefore, solvirrg problcrns tlrat had confound€dastronomersfor centuries.Galilt:orvasa lif'e-lorrg supporterof Copernicanism,and one of the early pionecrsol'the telescope.When he pointed his telescopeat the heavcns,he nrade a wealth of amazingdiscoveries,including mountains on tlle moon, a vast array of stars, sun-spots,and Jupiter's moons. All of thesc conflicted thoroughly with Aristotelian cosmology,and playetl a pivotal role in converting the scientific communitv to Copernicanism. Galileo'smost enduring contribution, however,lay not in astronomy but in mechanics,where he refuted the Aristotelian theory that heavier bodies fall faster than lighter ones. hr place of this theory Galileo made the counter-intuitive suggestionthat all

Galileo is generally regarded as the first truly modern physicist. He was the first to show that the language of mathematics could be usedto describethe behaviour of actual objects in the material world, such as falling bodies, projectiles, etc. To us this seems obvious - today's scientific theories are routinely formulated in mathematical language,not only in the physical sciencesbut also in biolory and economics.But in Galileo's day it was not obvious: mathematics was widely regarded as dealing with purely abstract entities, and hence inapplicable to physical reality. Another ' innovative aspectof Galileo's work was his emphasis on the importance of testing hypothesesexperimentally. To the modern scientist, this may again seem obvious. But at the time that Galileo was working, experimentation was not generally regarded as a reliable means of gaining knowledge. Galileo's emphasis on experimental testing marks the beginning of an empirical approach to studying nature that continues to this day. The period following Galileo's death saw the scientific rwolution rapidly gain in momentum. The French philosopher, mathematician, and scientist Ren6 Descartes(f596-165O) developeda radical new'mechanical philosophy', according to which the physical world consistssimply of inert particles of matter interacting and colliding with one another. The laws governing the motion of these particles or'corpuscles'held the key to understanding the structure of the Copernican universe, Descartes

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believed.The mechanical philosophy promised to explain all observablephenomena in terms of the motion of these inert, insensiblecorpuscles,and quickly becamethe dominant scientific vision ofthe secondhalf of the lJth centuryl to some extent it is still with us today.Versions of the mechanical philosophywere espoused by figures such as Huy$ens, Gassendi,Hooke, Boyle, and others; ils widespreadacceptancemarked the final downfall of the Aristotelian world-view.

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The scientific revolution culminated in the work of Isaac Newton (1643-172n, whose achievementsstand unparalleled in the history of science.Newton's masterpiecewas his Mathematical Principl,ea of Natural Philnsophg, published in 1687.Newton agreed with thc mechanicalphilosophers that the universe consistssimply of particles in motion, but sought to improve on Descartes'laws of motion and rules of collision. The result was a dynamical and mechanical theory of great power, based around Newton's three laws of motion and his famous principle of universal gravitation. According to this principle, every body in the universe exerts a gravitational attraction on every other body; the strength ofthe attraction between two bodies depends on the product of their masses,and on the distance between them squared.The laws of motion then specifuhow this gravitational force affects the bodiur' motions. Newton elaborated his theory with great mathematictl precision and rigour, inventing the mathematical technique we now call'calculus'. Strikingly, Newton was able to show that Kepler's laws of planetary motion and Galileo's law gf free-fall (both witlr certain minor modifications) were logical consequencesof his lnwn of motion and gravitation. In other words, the very same laws worrld explain the motions of bodies in both terrestrial and celestial domains, and were formulated by Newton in a precise quantitntivt' form. Newtonian physics provided the framework for sciencefor the ttcxt 2oo years or so, quickly replacing Cartesian physics. Scientific confidencegrew rapidly in this period, due largely to the successol'

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Newton's theory which was widely believed to hirvc rcvcalcd tltc true workings of r{ature, and to be capableof explaining cvcrytlring, in principle at least. Detailed attempts were made to exttrtrdthe Newtonian mode of explanation to more and more phcttontena. 'Ihe 18th and rgth centuries both saw notable scientific ittlvattccs, particularly in the study of chemistry optics, energ)', thermodynamics, and electromagnetism.But for the most part, these developmentswere regarded as falling within n broadly Newtonian conception of the universe. Scientists acccptecl Newton's conception as essentiallycorrect; all that remained to be done was to fill in the details. Confidencein the Newtonian picture was shattereclin the early years ofthe 2Oth century thanks to two revolutionary new developmentsin physics: relativity thqory and quantunr 0 mechanics.Relativity theory discoveredby Einstein, showed tlrat c {, Newtonian mechanicsdoes not give the right results whcn J{ o applied to very massiveobjects, or objects moving at very high E CL velocities.Quantum mechanics,conversely,shows that the I ..9 Newtonian theory doesnot work when applied on a very small f scale,to subatomic particles. Both relativity theory and quantum mechanics,especiallythe latter, are very strange antl radical theories, making claims about the nature of reality that nrany peoplefind hard to acceptor evenunderstand.'fheir emergence causedconsiderableconceptual upheaval in physics,which continues to this day. So far our brief account of the history of sciencehas focused mainly on physics.This is no accident,as physics is both historically very important and in a sensethe most fundamental of all scientific disciplines. For the objects that other sciencesstudy are themselves made up of physical entities. Consider botany, for example' Botanists study plants, which argultimately composcclof molecules and atoms, which are physical particles. So botany is obviously less fundamental than physics - though that is not to say it is any less important. This is a point we shall return to in Cltapter .3.Bttt even

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a brief description of modern science'sorigins would be incomplete if it omitted all mention of the non-physicalsciences. In biolory, the event that stands out is Charles Darwin's discovery of the theory of evolution by natural selct:tion,published in The Origin of Speciesin 1859. Until then it wiuswidely believed that the different specieshad been separatelycreated by God, as the llook of Genesisteaches.But Darwin argued that contemporary .specieshave actually evolved from ancestral ones,through a processknown as natural selection. Natural selection occurs when someorganisms leave more offspring than others, depending on their physical characteristics; ifthese characteristics are then inherited by their offspring, over time the population will become better and better adapted to the environment. Simple though this processis, over a large number of generations it can eauseone speciesto evolve into a wholly new one, Darwin argued. So persuasivewas the evidence Darwin adduced for his theorythat by the start of the 2oth century it was acceptedas scientific orthodoxy, despite considerable theological opposition (Figure a). Subsequentwork has provided striking confirmation of Darwin's theory which forms the centrepiece of the modern biological world-view. The 2oth century witnessed another revolution in biolory that is not yet complete: the emergenceof molecular biology, in particular molecular genetics. In 1953 Watson and Crick discoveredthe structure of DNA, the hereditary material that makes up the genes in the cells of living creatures (Figure.t). Watson and Crick's discoveryexplained how genetic information can be copied from one cell to another, and thus passeddown from parent to ofispring, thereby explaining why offspring tend to resembletheir parents. Their discoveryopened up an exciting new area ofbiological research.In the 50 years since Watson and Crick's work, molecular biology has grown fast, transforming our understanding of heredity and of how genesbuild organisms.The recent attempt to provide a molecular-level description of the complete set of genesin a human

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which studiesvariorrsaspecLsof hunran cognition such a^s perception,memory,learning,anclrea^soning, and has transfrrrrrrr.rl traditional psyclrology.Much of the irrrpetusfor cognitive scicn('(' comesfrom the idea that the human rnind is in some respects similar to a computer,and thus that hrrntanmental proccsses<.:urlx. understoodby comparing them to the operationscomputers('arry

significant r:vr:nlof't.lrt'lirst :t0 years is the risc of cogrtitivc sciencc,

out. Cognitivescienceis still in ils infancy,but promisesto reveal much about the workings of the minrl. 'I'he socialsciences, especiallyeconomicsand sociology,lravealso flourished in thc 2ot lr century tlrough many peoplebelievethey'still lag behind the natural sciencesin terms of sophisticationand rigour. This is :rrr issuewe shall return to in Chapter /.

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More rcsourccs hirvc bccn dcvoted to scientilic t'cscitrcltilr the last hundred yrrarsthan cvt:r bcftrre.One result has bccn ittt explosiott ol' new scienti(ic rlist:illlirtt:s,such as computer scicrtct'.artilicial a rttl neuroscience.Possiblt't ht' ntost intelligcncc, l i u grrist.i<'s,

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Whatis philosophy of science? The principal task of philosophy of scienceis to analysethe methods of enquiry used in the various sciences.You nray wonder why this task should fall to philosophers,rather than to the scientiststhemselves.This is a good question. Part of tlrc ansrveris that looking at sciencefrom a philosophical perspectiveallows us to probe deeper- to uncover assumptionsthat are implicit in scientific practice, but which scientists do not explicitly discuss.lb illustrate, consider scientific experimentation. Supposea scientist does an experiment and gets a particular result. He repeats the experiment a few times and keepsgetting the same result. After that he rvill probably stop, confident that were he to keep repeating the experiment, under exactly the same conditions, he would continue to get the same result. This assumption may seenrobvious, but as o philosopherswe want to question it. Why assumethat future C o I repetitions of the experiment will yield the same result? How do we o know this is true? The scientist is unlikely to spend too much time o puzzling over these somewhat curious questions: he probably has o o better things to do. They are quintessentially philosophical = a A questions,to which we return in the next chapter. So part of the job of philosophy of scienceis to clucstion assumptionsthat scientiststake for granted. But it rvould be wrong to imply that scientists never discussphilosophical issues themselves.Indeed, historically, many scientistsh:rve played an important role in the development of philosophy of science. Descartes,Newton, and Einstein are prominent exalnples.Each was deeply interested in philosophical questions about how science should proceed,what methods of enquiry it shoulcl use,hrxv much confidencewe should place in those methods, rvhcther there are -limits to scientific knowledge, and so on. As we shall see,these questionsstill lie at the heart of contemporary philosophy of science.So the issuesthat interest philosophers of scienceare not 'merely phil6sophical'; on the contrary, they have engagedthe attention of some of the greatestscientists of all. That having been

said, it must be admitted that many scicntists today take little interest in philosophy of science,anrl kn'w little about it. while this is unfortunate, it is not an indication tlrat philosophical issuesare no longer relevant. Rather, it is a consequenceofthe increasingly specializednature ofscience, and ofthc polarization between the sciencesand the humanities that characterizesthe modern education system. You maystill be wondering exactly what philosophyof scienceis alr about. For to say that it'studies the methods of science',as we did above,is not reallyto sayvery much. Rather than tryto provide a more informative definition, we will proceed straight to consider a typicat problem in the philosophy of science.

Science andpseudo-science

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Recall the question with which we began: w_hatis science? Karl Popper,an influential 2oth-century philosopher ofscience, thought rt that the fundamental feature of a scientific theory is that it should be falsifiable.To call a theory falsifiabte is not to say that it is false. Rather, it means that the theory makes some definite predictions that are capableofbeing tested against experience.Ifthese predictions turn out to be wrong, then the theory has been falsified, or disproved. so a falsifiable theory is one that we might discover to be false - it is not compatible with every possible course of experience.Popper thought that some supposedlyscientific theories did not satisfr this condition and thus did not deserueto be cailed scienceat all; rather they were merely pseudo-science. Freud'spsychoanalpic theory was one of poppey'sfavourite examplesof pseudd-science.According to popper, Freud's theory could be reconciled with any empirical findings whatsoever. Whatever a patient's behaviour, Freutlians could find an explanation of it in terms of their theory - they would never admit that their theory was wrong. Popper illustrated his point with the following example. Imagine a man who pushes a child into a river 13

with the intention of murdering him, and another man who sacrificeshis life in order to savethe child. Freudians can explain both men's behaviour with equal ease:the first was repressed,and the secondhad achievedsublimation. Popper argued that through the use of such conceptsas repression,sublimation, and unconsciousdesires,Freud's theory could be rendered compatible with any clinical data whatever; it was thus unfalsifiable. ..) The samewas true of Marx's theory of history Popper maintained. Manr claimed that in industrialized societiesaround the world, capitalism would give way to socialism and ultimately t
deflectedby the sun, this would have showed that Einstein was wrong. So Einstein's theory satisfies the criterion of falsifiability. Popper'sattempt to demarcate science from pseudo-science is intuitively quite plausible. There is certainly something fishy about atheorythat can be made to fit any empirical datawhatsoever. But somephilosophers regard Popper'scriterion as overly simplistic. Poppercriticized Freudians and Marxists for explaining away any data that appearedto conflict with their theories, rather than acceptingthat the theories had been refuted. This certainly looks like a suspiciousprocedure. However, there is some evidencethat this very procedure is routinely used by'respectable'scientists whom Popperwould not want to accuseof engaging in pseudoscience- and has led to important scientific discoveries. Another astronomical example can illustrate this. Newton's gravitational theory which we encountered earlier, made predictions about the paths the planets should follow as they orbit the sun. For the most part, these predictions were borne out by observation.However, the observedorbit of Uranus consistently difrered from what Newton's theory predicted. This puzzle was solvedin 18,1,6 by two scientists,Adams in England and Leverrier in France,working independently. They suggestedthat there wa^e another planet, as yet undiscovered,exerting an additional gravitational force orf Uranus. Adams and Leverrier were able to calculatethe mass and position that this planet would have to have, if its gravitational pull was indeed responsiblefor Uranus'strange behaviour.Shortly afterwards the planet Neptune was discovered, almost exactly where Adams and l-everrier had predicted. Now clearly we should not criticize Adams'and Leverrier's behaviour as'unscientifiC - after all, it led to the discovery of a new planet. But they did preciselywhat Popper criticized the Marxisls for doing. They began with a theory - Newton's theory of gravity which made an incorrect prediction about uranus'orbit. Rather than concluding that Newton's theory must be wrong, they stuck by 15

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v -i ' ! i. " the theory and attempted to explain awaythe conflicting observationsby postulating a new planet. Similarly, when capitalism showed no signs of giving way to communisrn, Marxists did not concludethat Marx's theory must be wrong, but stuck by the theory and tried to explain away the conflicting observationsin other ways. So surely it is unfair to accuseMarxists of cngagirrgin pseudo-scienceif we allow that what Adams and l,everricr did counted as good, indeed exemplary science?

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The philosopher Ludwig wittgerrstein argued that there is no 'ot. {ixedset of features that define what it is to be a'game'. Rather, there is a loose cluster of features most which are possessed by 'f most games.But any particular game may lack any of the features in the cluster and still be a game. The same may be true of science. If so, a simple criterion for demarcating scicnte from pseudo-science is unlikely to be found.

This suggeststhat Popper'sattempt to demarcate sciencefrom pseudo-sciencecannot be quite right, despite its initial plausibility. For the Adams/Leverrier example is by no means atypical. In general,scientists do not just abandon their theories whenever they conflict with the observational data Usually they look for ways of eliminating the conflict without having to give up thcir theory; this I is a point we shall return to in Chapter 5. And it is worth f; remembering that virtually every theory in scienceconflicts with ! someobservations- finding a theory that fits all the data perfectly is =g extremely difficult. Obviously if a theory persistently conflicts with ?tot" and more data" and no plausible ways of explaining away the J f, conflict are found, it will eventually have to be re.iectcd.But little progresswould be made if scientists simply abarrdonedthcir theories at th6 first sign oftrouble.

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The failure of Popper'sdemarcation criterion throws up an important question. [s it actually possibleto find sonreconrmon feature shared by all the things we call'science', antl not sh:rredby anything else?Popper assumedthat the answer to this question was yes. He felt that Freud's and Marx's theories were clearly unscientific, so there must be some feature that they lack and that genuine scientific theories possess.But whether or not we accept Popper'snegative assessmentof Freud and Marx, his assumption that sciencehas an'esseirtialnature'is questionable.After all, scienceis a heterogeneousactivity, encompassinga wide range of different disciplines and theories. It may be that thcy share some fixed set of features that define what it is to be a science,but it may l6

l7

2 Chapter Scientificreasoning

Scientistsoften tell us things about the world that we would not otherwise have believed.For example,biologists tell us that we are closelyrelated to chimpanzees,geologiststell us that Africa and South America used to be joined together, and cosmologiststell us that the universe is expanding. But how did scientists reach these unlikely-sounding conclusions?After all, no one has ever seen one speciesevolvefrom another, or a single continent split into two, or the universe getting bigger. The answer,of course,is that scientists arrived at thesebeliefs by a processof reasoning or inference. But it would be nice to know more about this process.What exactly is the nature of scientific reasoning?And how much confidenceshould we place in the inferencesscientists make? These are the tolrics of this chapter.

andinduction Deduction Logicians make an important distinction between deductive and inductive patterns of reasoning.An example of a piece of deductive reasoning,or a deductive inference,is the following: like rcd wine All Frenchrnen Pierreis a lirenchmatr Therefore.l'i<:rrclikcs rcrl winc

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The first two statements are called the premissesof the inference, rvhilethe third statement is called the conclusion. This is a detluctiveinference becauseit has the following property: if the premissesare true, then the conclusion must be true too. In other words, if it's true that all.Fr.enchmanlike red wine, and if it's true tha,tPierre is a Frenchman, it follows that Pierre does indeed like red wine. This is sometimes expressedby sayrngthat the premissesof the inference entail the conclusion. Of course,the premissesof this inference are almost certainly not true - there are bound to be Frenchmen who do not like red wine. But that is not the point. What makes the inference deductive is the existenceof an appropriate relation between premissesand conclusion,namely that if the premissesare true, the conclusion must be true too. Whether the premissesare actually true is a different matter, which doesnt afiect the status of the inference as deductive. Not all inferences are deductive. Consider the following example: The first five eggs in the box were rotten All the eggshave the samebest-beforedate stamped on them

Therefore,the sixth eggwill be rotten too This looks like a perfectly sensiblepiece of reasoning. But nonethelessit is not deductive, for the premissesdo not entail the conclusion.Even if the first five eggswere indeed rotten, and even if all the eggsdo have the same best-before date stamped on them, this does not guarantee that the sixth egg will be rotten too. It is quite conceivablethat the sixth egg will be perfectly good. In other words, it is logically possiblefor the premissei of this inference to be true and yet the conclusion false, so the inference is not deductive. Instead it is known as an inductive inference. In inductive inference,or inductive reasoning, we move from premissesabout objectswe have examined to conclusions about objects we haven't examined- in this example, eggs.

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cxamincda largc number of DS sufferersand fountl that eachhad an additional chromosome.They then reasonedinductively to the conclusionthat all DS sufferers,including onesthey hadn't examined,have an additional chromosotne.It is easyto seethat this inference is inductive. The fact that the DS sufferersin the sample studied had a7 chromosomesdoesnt prove that all DS sufferers do. It is possible,though unlikely, that the sample was an unrepresentativeone.

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This example is by no means an isolated one. In effect, scientists use inductive reasoningwhenever they move from limited data to a more general conclusion,which they do all the time. Consider,for example,Newton's principle of universal gravitation, encountered in the last chapter,which saysthat every body in the universe exerts a gravitational attraction on every other body. Now obviously, Newton did not arrive at this principle by examining evcry single body in the whole universe - he couldnt possibly have. Ilather, he saw that the principle held true for the planets and the sun, and for objects of various sorts moving near the earth's surface. From this data he inferred that the principle held true for all bodies. Again, this inference wir obviously an inductive one: the fact that Newton's principle holds true for some bodies doesn't gtrarantee that it holds true for all bodies.

for humans.The word'proof should strictly only be usedwhen we are dealing with deductive inferences. In this strict senseof the word, scientific hypothesescan rarely, if ever,be proved true by the data. Most philosophersthink it's obvious that sciencerelies heavily on incluctivereasoning,indeed so obvious that it hardly needs arguing for. But, remarkably, this was denied by the philosopher Karl Popper,who we met in the last chapter. popper claimed that scientistsonly need to use deductive inferences.This would be nice if it were true, for deductive inferences are muih safer than inductive ones,as we have seen. Popperbbasic argument was this. Although it is not possible to provethat a scientifictheory is true from a limited data sample,it ir possibleto prove that a theory is false. Supposea scientist is consideringthe theory that all piecesof metal conduct electricity. Evenif every piece of metal she examines does conduct electricity, this doesnt prove that the theory is true, for reasonsthat weve seen. But if she finds even one piece of metal that does not conduct electricity,this does prove that the theory is false. For the inference from'this pieceof metal doesnot conduct electrici!y'to,it is falsethat all piecesof metal conduct electricity' is a deductive inference- the premissentails the conclusion.so if a scientist is only interested in demonstrating that a given theory is false, she may be able to accomplishher goal without the use of inductivc inferences.

T.becentral role of induction in scienceis sometinles ollscureclby the way we talk. For example,you might read a newspaperreport that saysthat scientistshave found'experimental proof that genetically modified maize is safeforhumans. What this means is The weaknessof Popper'sargument is obvious. For scientists are that the scientistshave tested the maize on a large number of not only interested in showing that certain theories are false. when humans,and none of them have cometo any harm. But strictly a scientistcollectsexperimentaldata, her aim might be to show tlrat in in the sense speaking this doesn'tproae that the maize is safe, which mathcntaticianscan prove Pythagoras'theorem,say.For the a particular theory - her'arch-rival's theory perhaps - is false. llrrt inferencefrom 'thc maizcdidn't harm any of the peopleon whom it much more likely, she is trying to convince people that her own theory is true. And in order to do that, she will have to resort to was testcd'to'thc tnaizcwill not harm anyone'is inductive, not inductive reasoning of some sort. so popper's attempt to show that deductivc.'l'hcncwspitpcrrcpott should really have said that qxtt'ctttt:ly science is maize safe can liet by without induction does not succeed. goodeoidmcethat the scientistslrlvc liltuttl 22

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Hume'sprobfem Although inductive reasoning is not logicallywatertight, it rronethelessseemslike a perfectly sensibleway of forming bericfs about the world. The fact that the sun has risen every day up untir now may not prove that it will rise tomorrow, but surely it gives us vcry good reasonto think it will? If you came across someonewho professedto be entirely agnostic about whether the sun will rise tornorrow or not, you would regard them as very strange indeed, if not irrational.

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llut what justifies this faith we place in induction? How shourcru,e g'about persuadingsomeonewho refusesto reason inductively thnt thcy are wrong? The l8th-century scottish philosopher David llunre (t7tt-t776) gavea simple but radical answer to this clucstion.He argued that the use of induction cannot be ration:rily justilicd at all. Hume admitted that we use induction ail the time, in cvcrydaylife and in science,but he insisted this wasjust a mrttcr of brute animal habit. If challengedto provide good a reusotlfor using induction, we can give no satisfactory answer,he thought. I low
true' llut how do we know that the uN assrtmptittnis actually (in the strict Hurne asks?Can we perhaps prove its trtttlt srlmehow easyto imagine senseof proof)? No, saysHume, we cantlttt' l"tlr it is its cOurse a universewhere nature is not uniform, bttt changes might ranclomlyfrom day to day. In such a univet'sc' computers sometimesexplodefornoreason'watermiglrtsometimesintoxicate stop dead on us without warning, billiard balls might sometimes is colliding,and so on. Sincesuch a'non-unifbrm' universe truth of uN. conceivable,it follows that we cannot strictly prove the For if we coulcl prove that UN is true, then the non-uniform universewould be a logical impossibility' hope to Granted that we cannot prove UN, we might nonetheless has UN find gooclempirical evidencefor its truth' After all' since for always held true up to now, surely that gives us good reason says thinking it is true? But this argument begs the question' depends itself so and Hume! For it is itself an inductive argument, from the on the UN assumption. An argument that assumesUN put the To is true' outset clearly cannot be used to show that UN has point another way, it is certainly an establishedfact that nature this to behavedlargely uniformly up to now' But we cannot appeal this fact to argue that nature will continue to be uniform' because guide to assumesthat what has happened in the past is a reliable whatwillhappeninthefuture-whichistheuniformityofnahrre we end assumption. If we tryto argue for UN on empirical grounds' up reasoning in a circle howyou The force of Hume's point can be appreciatedby imagining would go about persuading someonewho doesnttrust inductive reasoningthattheyshould.Youwouldprobablysay:.look,inductive rea^soninghas worked pretty well up until now' By using induction invented scientistshave split the atom, landed men on the moon' cornputers, and so on. Whereal people who haven't used induction have tended to die nasty deaths.They have eaten arsenic believing that tlrnr it would nourish them, jurnped offtall buildings beliwing theywouldfly,andsoon(Figure6).Thereforeitwillclearlypayyou

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to reasoninductively.'But of coursethis wouldn't convincethe doubtcr'.Iior to argue that induction is trustworthy becauseit has worketl well up to now is to ieason in an inductive way. Such an argumcnt would carry no weight with someonewho doesnt already trust induction.'Ihat is Hufn€'s fundamental point. Sothe position is this. Hume points out that our inductive inferencesrest on the UN assumption. But we cannot prove that UN is true, and we cannot produce empirical evidencefor its truth without beggingthe question.So our inductive inferencesrest on an assumptionabout the world for which we haveno good grounds. Hume concludesthat our confidencein induction is just blind faith - it admits of no rational justification whatever. This intriguing argument has exerteda powerful influenceon the philosophyofscience,and continuesto do so today.(Popper's unsuccessfulattempt to show that scientisls need only use deductiveinferenceswas motivated by his belief that Hume had shown the total irrationality of inductive reasoning.)The influence of I Iurne'sargument is not hard to understand.For normally we think of scienceas the very paradigm of rational enquiry.We place great laith in what scientiststell us about the world. Every time we travcl by aeroplane,we put our lives in the hands of the scientislq who clesignedthe plane. But sciencerelies on induction, and Hume's argument seemsto show that induction cannot be rationallyiustified. If Hume is right, the foundations on which scienceis built do not look quite as solid as we might havehoped. This puzzling state of affairs is known as Hume's problem of induction. Philosophershave respondedto Hume's problem in literally dozens of dill'erent ways; this is still an active area of researchtoday. Some peoplc believe the key lies in the concept of probability. This suggcstionis quite plausible.For it is natural to think that although the premissesof an inductive inference do not guarantee the truth of the conclusion, they do make it quite probable. So even if

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I las Stralvson really succeededin defusing Hume's problern? Some philosopherssayyes, others say no. But most people agrcc tlrat it is vcry hard to seehow there could be a satisfactoryjustificat.iou of induction. (Frank Ramsey,a Cambridge philosopher fronr l}r: 192Os,said that to ask for a justification of induction wirs 'to urv frrr the moon'.) Whether this is something that should worry trs, or shake our faith in science,is a difficult question that you shorrld ponder for yourself.

to the bestexPlanation lnference so far have all had l'he inductive inferenceswe've examinsl the premiss of the essentiallythe same structure' In each ca^se' so far have been y'' inference has had the form 'all x's examined next x to be examined and the conclusionhas had the form'the
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ltisobviousthatthisinferenceisnon.clccluctive:thepremissesdo have been stolen not entail the conclusion. For the cheesecould to make it look like by the maid, who cleverly left a few crumbs scratching noises the handiwork of a mouse (Figure 7)' And the ways - perhaps they could have been causedin any number of the inference is were due to the boiler overheating. Nonetheless, that a mouse ate the clearly a reasonableone. For the hypothesis of the data than do cheeseseemsto provide a better explanation maids do not the various alternative explanations. After all, do not tend to normally steal cheese,and modern boilers when they get the overheat.Whereas mice do normally eat cheese So although we chance,ancl do tend to make scratching sounds' is true, on balance it cannot be certain that the mouse hypothesis for the looks quite plausible: it is the best way of accounting available data.

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hangs on whiclr different types of non-deductive inference' Nothing we stick to it choiceof terminology we favour, so long as consistentlY. argued for his Scientistsfrequently use IBE' For example' Darwin facts about the theory of evolution by calling attention to various that current living world which are hard to explain if we assume make perfect senst' specieshave been separatelycreated,but which ancestors'as his if current specieshave descendedfrom common similaritics theory held. For example, there are close anatomical we explain thie' if berweenthe legs of horses and zebras' How do he could God created horses and zebrasseparately?Presumably But if horses entl havemade their legs as difierent as he pledsed' ancestor' thin zebrashave both descendedfrom a recent common providesanobviousexplanationoftheiranatomicalsimilarity' facts of thitl Darwin argued that the ability of his theory to explain evidence sort, and of many other sorts too, constituted strong

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Reasoningof this sort is known as,inferenceto the best explanation', for obvious reasons,or IBE for short. Certain terminologicalconfusionssurround the relation between IBE ancl induction. some philosoprrersdescribeIBE as a type of inductive inference;in effect,they use ,incluctiveinference'to mean 'any inferencewhich is not deductive'.others contrast IBE.with inductive inference, as we h*ve done above.on this way of cutting the pie,'inductive inference'isreservedfor inferencesfrom examinedto uncxarnincdinstnncesof a given kind, of the sort we examinedearlier.;IIlli *nd i'clut:tivc inferenceare then two

work on Brownian Another example of IBE is Einstein's famous of motion. Brownian motion refers to the chaotic' zig'zagmotion gas' It was diccoveretl microscopic particles suspendedin a liquid or (1ne-1858)' whlle in 1827 by the Scottish botanist Robert Brown of attempted examining pollen grains floating in water' A number lgth the in explanations of Brownian motion were advanced One theory attributed the motion to electrical attraction ""rrtrlry. surrounding;' between particles, another to agitation from external correct The fluid' the in and another to convection currents which saystltet explanation is based on the kinetic theory of matter' liquidsandgasesaremadeupofatomsormoleculesinmotion''l.lte molecules' suspendedparticles collide with the surrounding first observed' causing the erratic, random movements that Brown century but was nttt This theory was first proposed in the late $th widelyaccepted,notleastbecausemanyscientistsdidntbelievt: But in 1905' that atoms and molecules were real physical entities. treatment of Einstein provided an ingenious mathematical 31

Ilrownian motion, making a number of precise,quantitat.ivc prcdictionswhich were later confirmed experimentally.Alicr. li'stein's work, the kinetic theory was quickly agreedt' pr'r'itrc a ftrr better explanation of Brownian motion than any of tlre tltcrnatives, and scepticism about the existenceof atoms a.n
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one interestingquestionis whether IBB or ordinary ind.ctirn is a tnore fundamentalpattern of inference.The philosopher Gilbcrt I larman has argued that IBE is more fundamental. Accorcling t
irtthrction.'Ihusit is tlrirthas bccn gainedthrough ortlinlry mode of inference' int:orrcctto regardlllli as a morc litttdirrltcrttal one issueclearly Wltichevcr o{ theseopposingvicws wt: litvtlttr' llSE' we need someway dcmandsmore attention' lf we want to ttsc providesthe best of clecidingwhich of the competing hypothcses explanationofthedata.Butwhatcrittlria
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explanationof the data' 'l'hc icleathat simplicity or parsimony is the mark of a good flesh out the idea cxplanationis quite appealing,and ccrtainlyhelps guide to inference'this of IBIi. Ilut if scienti,t'' u'e simplicity as a the universe is simple ririsesa problem. For how do we know that explains the data in rather than complex? Preferring a theory that sensible' But is terms of the fewest number of causesdoes seem a theory is more there any objective re:Fon for thinking that such of science likely to be true than a less simple thcory? Philosophers question'
andinduction Probability the '['he conceptof probability is philosoplricallypuzzling' Part of have more than one puzzleis that the word'probability sccmsto 33

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mcani'g' lfyou readthat the probab'ity of an Englishwonranriving to IOOyearsof age is I in IO, you would understand this as saying that one-tcnth of ail Engrishwomenlive to the ageof roo. sim'arry, ifyou read that the probab'ity of a mare smoker deveropingrung cancer is I in 4.,you would take this to mean that a quarter of all male smokers develop lung cancer.This is known a.sthefrequency interpretation of probability: it equatesprobabilities with proportions, or frequencies.But what ifyou read that the probability of finding life on Mars is I inl,ooo? Doesthis mean that one out of every thousand planets in our solar sy.stemcontains life? clearly it doesnot. For one thing, there are only nine praneLsin our solar system.So a difierent notion of probability must b" at work here.

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one interpretation of the statement'the probability of life on Mars is 1 in I,OOO'isthat the personwho utters it is simply reporting a subjectivefact about themselves- they are teling r* ho* rikerythey think life on Mars is. This is the subjettive interpretation of probability. It takes probability to be a measure of the strength of our personal opinions. Clearly,we hold some of our opinions more strongly than others. I am very confident that Brazil win win the World Cup, reasonablyconfident that Jesus Christ existed, and rather lessconfident that global environmentar disa^stercan avbrted.This could be expressedby sayrng 'e that I assign a high probability to the statement'Brazil will win the worrd cup,, a fairry high probability to 'Jesuschrist existed', and a low prubrbility to global environmental disaster can be averted,.Of course,to put a. exact number on the strength of my conviction in these statements would be hard, but advocatesofthe subjective interpretatio' regard this as a merely practicallimitation. In principre, we shourdbe able to assignaprecise numericar probability to each of the statements about which we have an opinion, refleciing how strongry we berieve or disbelievethem, they say. Thesubjective interpretation of probability impries that there are no objective facts about probability, independently of what people

believe.If I say that the probability of finding life on Mars is high and you saythat it is very low, neither of us is right or wrong - we are both simply stating how strongly rve beliwe the statement in question.Of course,there is an objective fact about whether therc is life on Mars or noti there is just no objective fact about how probable it is that there is life on Mars, according to the subjective interpretation. The logical interpretation of probability rejects this position. It holds that a statement such as'the probability of life on Marg is high'is objectively true or false, relative to a specifiedbody of evidence. A statement's probability is the measure of the strength of evidence in its favour, on this view. Advocates of the logical interpretation think that for any two statements in our language' we can in principle discover the probability of one, given the other as evidence.For example, we might want to discover the probability that there will be an ice age within lo'Ooo years' given the current rate of global warming. The subjective interpretation saysthere is no objective fact about this probability. But the logical interpretation insists that there is: the current rate of global warming confers a definite numerical probability on the occurrence of an ice age within lo,ooo yearl' sayo.9 for example. A probability of o.9 clearly counts as a hlgh probability - for the ma.ximum is 1 - so the statement'the probability that there will be an ice age within lo'ooo years is high'would then be objectively true, given the evidence about globalwarming. If you have studied probability or statistics, you may be puzzletl by this talk of difierent interpretations of probability. How do thene interpretations tie in with what you learned? The answer is that tho mathematical study of probability does not by itself tell us what probability means, which is what we have been examining above. Most statisticians would in fact favourthe frequency interpretntion' but the problem of how to interpret probability' like most philosophical problems, cannot be resolvedmathematically. Thc

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nltthcnlrtical fbmrulaefor working out probabilitiesrenrairrtlrc strnc, whiclrevcrinterpretationwe adopt. l'lrilosophersof scienceare interested in probability for. trv, nrain rciLsons. I'he first is that in many branchesof science,espccially and biology,we lind laws and theories that are firrrnrrlated llhy.sics usingthe notion of probability.Consider,for example,the tht:ory krr,rv'as Mendeliangenetics,which dealswith the tr.nsr'issirn rfgcnes from one generationto another in sexuallyreprorluciug populations.one of the most important principles of Me.dcri.n gcrreticsis that everygene in an organism has a sov" clr.'cc of lnaking it into any one of the organism's gametes(sperm or egg cclls). Hence there is a So% chancethat any gene founcl in your lttother will also be in you, and likewise for the genesin your. lathcr. Using this principle and others, geneticistscan provicle at dctailed explanationsfor why particular characteristics(e.g. eye colorrr) are distributed acrossthe generations of a family i. the il I way that they are. Now'chance, is just another word for probability, so it is obvious that our Mendelian principre makcs cssentialuse of the concept of probability. Many other exanrpres could be given of scientific laws and principles that are exprc.ssecl in terms of probability. The need to understand these rarvsancl principlesis an important motivation for the philosophical st'dy of' probability.

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'I'he secondreasonwhy philosophers

of scienceare intercsterl i' the concept of probability is the hope that it might shed so're light o. i'ductive inference,in particular on Hume's problem; tlri.s.slrrtll bc our focushere.At the root of Hume's proflem is the fact th*t the prcmissesof an inductive inferencedo not guaranteethe truth of its conclusion.But it is tempting to suggestthat the premissesof a typical inductive inference do make the conclusion highlv probable. Although the fact that all objects exdmined so far obey Ne*ton's larv of gravity does't prove that ail objects do, surely it does rnake it very probable?So surely Hume's problem can be ans*,erecl
However, matters are not quite so sitnllle. For we must ask what interpretation of probability this responseto Hume assumes.On to say it is highly probable that all the frequency tnte oU;ecrtoUeyNewton's law is to say that a very high proportion of all objects obey the law. Eut there is no wav we can know that, unless we use induction! For we have only examined a tiny fraction . So llume's problem remains. in the of all the "bjects Another way to seethe point is this. We began with the inference from'all examined objects obey Newton's lau/ to'all objects obey Newton's lad. In responseto Hume's worry that the premiss of this inference doesnt guarantee the truth of the conclusion, we suggestedthat it might nonethelessmake the conclusion highly probable. But the inference from'all examined objects obey Newton's law'to'it is highly probable that all objects obey Newton's lad is still an inductive inferenee,given that the latter means 'a very high proportion of all objects obey Newton's lau/, as it does according to the frequency interpretation. So appealing to the concept of probability does not take the sting out of Hume's argument, if we adopt a frequency interpretation of probability. For knowledge of probabilities then becomesitself dependent on

The subjective interpretation of probability is also powerlessto solve Hume's problem, though for a different reason.SupposeJohn believesthat thr! sun will rise tomorrow and Jack believesit will not. They both acceptthe evidencethat the sun has risen every day in the past. Intuitively, we want to say that John is rational and Jack isnt, becausethe evidencemakes John's belief more probable. But if probability is simply a matter of subjective opinion, we cannot say this. All we can say is that John assignsa high probability to 'the sun will rise tomorrod and Jack does not. If there are no objective facts about probability, then we cannot say that the conclusions of inductive inferences are objectively probable. So we have no explanation of why someonelike Jack, who declines to use induction, is irrational. But Hume's problem is precisely the demand for such an explanation.

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Chapter 3 Explanationin science

coveringlaw modelof dxplanation Hempel's

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One of the most important aims of scienceis to try and exlllain w.hat happensin the world around us. Sometimeswe seekexpl:urations for practical ends. For example,we might want to know wlrv thc ozonelayer is being depleted so quickly, in order to try and clo somethingabout it. In other fitseswe seekscientificexplanntions simply to satisfr our intellectualcuriosity - we want to underrstand more about how the world works. Historically, the pursrrit ol' scientific explanation has been motivated by both goals.

rvlryquestion.Ifwecoulddeterminetlreessentialfeaturesthatstrclt explanation is' an answer must have,we would know what scientific have the Hempel suggestedthat scientific explanations typically followed by t logical structure of an argument, i'e' a set of premisses that needs conclusion.The conclusionstatesthat the phenomenon f why the explaining actually oecurs'and the premissestell us sugar dissolvcs conclusionis true' Thus supposesomeoneaskswhy To answer it' in watcr.'l'his is an explanation-seekingwhy question' conclttsionis saysHenlpel, we must construct an argument whose 'sugardissolvesin watcr'and whose premissestell us why this of scientific conclttsionis true.'fhe task of providing an account preciselytlrtl cxlllanatitln then becomesthe task of characterizing a conclttsiott. rclation that must hold betweena set rlf premissesand latter.'l'hnt the in oKler tor the former to count as an explanationof

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Quite often, modern scienceis successfulin its aim of supplving explanations.For example,chemistscan explainwhy sodirrrrrtrrrns yellow when it burns. Astronomerscan explain why solar cclipscs occurwhen they do. Economistscan explain why the yen rlcclinc
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But what exactly is scientific explanation?What exactly rlot:sit 'l'his meanto saythat a phenomenoncan be'explained'bysciclrct,? is a questionthat has exercisedphilosopherssinceAristotlc, lrrrt our starting point will be a famous accountof scientificexplanationput forward in the 195osby the American philosopherCarl Hen-rperl.

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the Hernpel'sanswerto the problem was three-fold' Firstly' shottltl lttr premisscsshoukl entail the conclusion,i'e' the argument Thirdly' true. be a rlcductiveone. secontlly,the premissesshould all generallaw' General , the prernissesshoulclconsistof at leastone ' body's l"*, ore things such as'all metals conduct electriciQy'"a contain plants accelcration varies inversely with iusma^ss"'all facts such as chlorophyll', and so on; they contrast rvith particular 41

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luetrdconductselectrici!y','the prant on mv cresk 'f contitittscltklrollhyll'1ndso on. Generallawsare sometil.l.res r:alled 'laws I rcnrpclallowedihat scientificexplan.tion c'ulcl 'l'rr'l,uru'. " *ppcal tr p*rticulrr factsas well asgeneral laws,bui hc herclthat at lcast onc gcucral law was alwaysessential.So to explain a phenonrcnon,on l{empel'sconception,is to showthat its occurrence follows deductivelyfrom a generallaw, perhaps supplementeclby other laws and/or particular facts,all of which must be true. To illustrate,supposeI am trying to explainwhy the plant on rnv deskhas died. I might offer the following explanation. orving tr'the poor light in my study,no sunlight has been reachingthe plant; but sunlight is necessaryfor a plant to photosynthesize; ancl without photosynthesisa plant cannot make the carbohydrates it needst' survive, and so will die; therefore my plant died. This expranation et fits Hempel's model exactly.It explains the death E of the plant by s deducing it from two true laws - that sunlight is necessaryfor o photosynthesis,and that photosynthesisis necessaryfor survival _ 3 A and one particular fact - that the plant was not getting any sunlight. o Given the truth of the two laws and the particular € c fact, the dcath'f I the plant hadto occur; that is why the former constitute a goocl explanation of the latter. schematically, Hempel's model of explanation can be written as follows: Generallaws Particular facts = Phenomenonto be explained

The phenomenonto be explaincclis called the erplanandunt, and the general laws and particular facts that do the explaining are called the erplana,as.'fhcexplanandumitself may be either a particular fact or a gencral law. Irr thc example above,it was a particular firct - the rlcatlr.f nry pra't. Iltrt sometimesthe trri'gs rve

want to explain are general. For example,we mightwish to expltilr why exposureto the sun leadsto skin cancer.This is a generallaw, not a particular fact. To explain it, we would need to deduce it frottt still more fundamental laws - presumably,laws about the impact ol' radiation on skin cells, combined with particular facts about thrr amount of radiation in sunlight. So the structure of a scientific explanation is essentiallythe same,whether lhe etplanandum, i't'' the thing we are tryrng to explain, is particular or general' It is easyto seewhy Hempel's model is called the covering lnw model of explanation.For accordingto the model, the essenceof explanation is to show that the phenomenon to be explained in 'covered'by some general law of nature. There is certainly something appealing about this idea. For showing that a phenomenonis a consequenceofa generallaw doesin a sensetnkn the mystery out of it - it renders it more intelligible. And in fnct, scientific explanations do often fit the pattern Hempel descrlber, For example,Newton explained why the planets move in elllprer around the sun by showing that this can be deduced from hls Inw o[ universal gravitation, along with some minor additional Newton's explanation fits Hempel's model exaetly: n a^ssumptions. phenomenon is explained by showing that it had to be so, given tlre laws of nature plus some additional facts. After Newton, there wtu no longer any mystery about why planetary orbits are ellipticnl.

Hempel was aware that not all scientific explanations fit his mtxlcl exactly.For example, if you ask someonewhy Athens is alwayn immersed in smog, they will probably say because of car exhnttsl pollution'. This is a perfectly acceptablesdientificexplanation, though it involvesno mention of any laws. But Hempel wottltl stty that if the explanation were spelled out in full detail, laws wottltl enter the picture. Presumablythere is a law that sayssometlring like ,if carbon monoxide is releasedinto the earth's atmosphere in . suflicient concentration' smog clouds will form" The full explanation of why Athens is bathed in smog would cite this lnw along with the fact that car exhaust contains carbon monoxitle ntttl

.,' Athens has lots of cars.In practice,we wouldn't spell otrt tlr
I'lcrnpel drew an interesting philosophical consequencefr.r' his nrodel about the relation between explanation and prcdicti.n. fle argued that these arg two sidesof the same coin. wherevcr *'e gi'c it covering law explanation of a phenomenon, the larvs nntl particular facts we cite would have enabled us to preclict thcr occurrenceof the phenomenon,if we hadnt alreadykrr.u,rr ;rlxrutit. 'lb illustrate, consider again Newton's explanation of rvhy, lllanctar.y orbits are elliptical. This fact was known long before Ncrvto, cxplained it using his theory of gravity - it was discovcrccllrv Kcplcr. llut if it had not been known, Newton would have bee' ablcrt' prcdict it from his theory of gravity, for his theory entails that planetary orbits are elliptical, given minor additional asstrrnptio'rs. l-Iernpelexpressedthis by saylng that every scientific exlrla'*ti.n is potentially a prediction - it would have servedto pre
of things that dn frtthe coveringlaw otherhancl,thereareca-res model,but intuitivelydo not countasgenuinescientific ThesecasesEuggesttlrtt Hempel'smodelis too explanations. liberal - it allowsin thingsthat shorrlclbeexcluded.we will focuson of the secondsort. counter-examples

Theproblemof symmetry Supposeyou are lying on the beach on a sunny day, and you notice that a flagpole is casting a shadow of 20 metres acrossthe sand (Figure 8).

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Though the covering law model captures the structure rn^ny 'f actual scientific explanations quite well, it also facesa r-rumbcr of awkward counter-examples.These counter-examples{.ll int' two classes.on the one hand, there are casesof genuine scicntific explanationsthat do not fit the covering law model, even approximately.These casessuggestthat Hempel's modcl is too strict - it excludes somebonafide scientific explanatio.s. orr the

15 metre flagpole

1?,s"if g. A l5-metre flagpolecastsa sharlowof 20 metreson the beachwhen the sun is 3?ooverhead. Someoneasksyou to explain why the shadow is 2o metres long' This is an explanation-seekingwhy question. A plausible answer might go as follows: 'light rays from the sun are hitting the flagpole' which is exactly 15 metres high. The angle of elwation of the sun is 3?.. Since light travels in straight lines, a simple trigonometric calculation (tan 37o =tSlZO) shows that the flagpole will cast a shadow 20 metres long'. This looks like a pert'ectlygood scientific explanation' And by rewriting it in accordancewith Hempel's schema,we can seethat it fits the covering law model:

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of thc llrglxrlc :urd the angleof elevationof the sun, along with the ,pl,it'*l ltw that light travelsin straight lines and the laws .f lrig,norrrctry.since theselaws are true, and sincethe flagpoleis irrrh,ctll,l)nrctreshigh, the explanationsatisfiesHempel's n'rlrrirtlrrcntsprecisely.So far so good.The problem arisr:sas lirllrws. sulrlrosewe swap the euplnnandum- that trre shacrow is 2O rnr:trcslong - with the particular fact that the {lagp'le is ll rrrctrcslrigh.The resultis this:

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Flagpole is 15 metres high

'l'his'cxplanation'clearlyconformsto the covering larv pattem too. 'l'he height of the flagpole is deducedfrom the length of the shad'r,v it castsand the angle of elevation of the sun, along with the optical law that light travels in straight lines and the laws of trig..onretry. But it seemsvery odd to regard this as an arplanatfon of rr4rythe llagpoleis 15 metreshigh. The real explanationof why trrc flagpole is 15metreshigh is presumablythat a carpenterdelibcratcll, it so - it has nothing to do with the length of the shadorvtlurt it'radc casts. So Hempel'smodel is too liberal: it allowssomethingto c.u't as a scientific explanation that obviously is not.

is that the concept of The general moral of the flagpole example The height of thc explanation exhibits an important asymmetry' shadow' given the relevant laws flagpol" explains the len$h of the In general' ifx explains y' and aclditional facts, buinot vice-versa' facts' then it will not be tnttr given the relevant laws and additional facts'This is sometimes explainsx, given the samelaws and it relation' "r, by saying that explanation is an asymmetric "*pr".r"d not respect this asymmetry' ltor Hempel's covering law model does justas$/ecandeducethelengthoftheshadowfromtheheiglrtrr|. "th" facts' so we can detlrtctr fltgpol", given the laws and aclclitional of the shadow' In otltcr the height of the flagpole from the length lx' n implies that explanation shoultl words, the coveringiu* So Hempel's rrrork'l -oa"t symmetric relation, but in fact it is asymmetric' scientific explanation' fuit" tn capture fully what it is to be a providesa counter-exampk'trr The shadowand flagpolecasealso prediction are two sitlesol'llre Hempel'sthesisttraiexplanation and you didn't know how samecoin. The reasonis obvious.Suppose you that it wa'scastitrgtr high the flagpolewas' If someonetold was 3f overhead'yotr shadowof 2o metres and that the sun given that yrlrrkttew would be able to predicttheflagprrle'sheight, laws' But as we hnvr''ittHt the relevantoptical and trigonometrical docsn't etplainyhy the flagpolehnn seen,this information "I"*ily prediction and expltrnttliott the height it does.So in this example predict a fact before wt: kttow part ways. Information that servcsto fact after we know it' wlrit:lr it doesnot serveto explain that same contradicts HemPel's thesis'

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TheProblemof irrelevance

in a room full of prcgrtattt Supposea young child is in a hospital personin the room - who is n women. The child noticesthat one asksthe doctorwhy trot"l'ltt' man calledJohn - is not pregnant' and

cloctorreplies:.Johnhasbeentakingbirth-controlpillsregrrlnrly pills regrrlnrly the last few years. Peoplewho take birth-control has not becomeprt'gltartt" neverbecom" p."grru,,,' Therefore' John 47

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l,et us supposefor the sakeof argun.lentthat s'hat thc rioctor.sa.\.s it true - John is mentally ill and doesindeedtake birth-crntr.l pills, which he believeshelp him. Evenso,the doctor'sreply to trrcchild is clearlynot very helpful. The correct explanationof wh1,.Iohnhas not becomepregnant,obviously,is that he is male and nralesr':rnrrot becornepregnant. However,the explanation the doctor has given the child fits t.he coveringlaw model perfectly.The doctor deducesthe plrenorrrcnon to be explained - that John is not pregnant - from the gcncral lau, that peoplewho take birth-control pills do not becomepregrrant and the particular fact that John hasbeentaking birth-crrntr.rrpills. Sinceboth the generallaw and the particular fact are tnrc, *nrr since they do indeed entail the erplunandurz, according to the covcring law model the doctor has given a perfectly adequateexpl;rn.ti'n rf (, why John is not pregnant. But of course he hasn't. Hence tlre o covering law model is again too permissive: it allows things to count o as scientific explanationsthat intuitively are not. €(t o o s A.

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The gcneralmoral is that a good explanationof a phenomcnorr should contain information that is releaantto the phenonrcrolr's occurrence.This is where the doctor'sreply to the child gocs\\,r.ong. Although what the doctor tells the child is perfectly true, thc {irct that John has been taking birth-control pills is irrelevant to his .ot being pregnant,becausehe wouldnt havebeen pregnant cven i{'he hadnt beentaking the pills. This is why the doctor'sreply rlocsrrot constitutea good answerto the child's question.Hempcl's rrro
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Explanation andcausality Sincethe coveringlaw model encountersso many problcms, it is natural to look for an alternative way of understanding scientific explanation.Somephilosophersbelievethat the key lies in thc concept of causality.This is quite an attractive suggestion.Iror in many casesto explaina phenomenonis indeedto saytvhitt carrsed

an investigatoris trying to explain it. lior cxatrtplc,il'ntt irccirltrtrt crash' the ltxrking for the causeof aeroplatttlcritslt,ltt: is obviottsly wa^sthe tlid thc plirnccrash?'and'what lndeecl,the
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the sun. accounts are not fully However, the covering law and cattsal many eqrrivalent- in somecasesthey diverge'"Indeed' precisely philosophersfavour a causalaccotlnt ofexplanation of the problems facing the becattsethey think it can avoid some problem' Why do-our covering law model' Recall the flagpole the flagpole explains the length intuitions tell us that the height of not vice-versa?Plausibly' of the shadow,given the laws' but is the causeof the shadow being becausethe height of the flagpole 2o metres long is not the 20 metreslong, but the shadowbeing high' So unlike the-covering causeof the flagpolebeing 15 metres givesthe'right'answer law model, a causalaccountof explanation intuition that we cannot in the flagpole case- it respectsour

explain the height of the flagpole by pointing to the lengrh of the shadow it casts. l'he general moral of the flagpole problem was that the covering law model cannot accommodate the fact that explanation is arr ir"symmetricrelation. Now causality is obviously an asymmetric rclation too: if x is the cause ofy, tien y i, ,rot the cause x. l..r cxaruple'ifthe short-circuit causedthe fire, then the nr" 'f.t"orty did not causethe short-circuit. It is thereforequite prausibrc to suggestthat the asymmetry of explanation derives from the &symmctry of causality.If to explain a phenomenon is to say what cuuscdit, then since causality is asymmetric we should expect cxpl*nation to be asymmetric too - as it is. The covering law model rtllls uP against the flagpole problem preciselybe"r.r." i, tries ro lndysc the concept of scientific "*plur,rtio'without referenceto cuusnlity.

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'l''c srnr'ois true of the birth-contror p'r case. That John takes birtlr-control pills doesnot explain *nV fr" isnt pregnant,bccause tlrc birth-control pills ar" not the oifri, not being l)regn.nr. l,lr'lrcr' John'sgenderiJ the cause"u.r* of his not being pregna't. .r.rr:rt is wlry wc think that the correct answerto the question.wrryis .lirlrrr rrot prcgnant?'is'becausehe is a man, and men cant become prcgnant', rather than the doctor,s answer.The doctor,s answer satisliesthe coveringlaw model, but sinceit doesnot correctly idc'tily the causeof the phenomenor, *" *rf, to explain, it clres not constitute a genuine explanation. The general moral we drew fr.'rn thcbirth-control pill example was that"a genuine scientific cx'lanation must contain information that is rerevantto the Wlanandum. In effect, this is another way of saying that the cxtrrlanationshould tell us the explanandu*,"cause. Causality_ basedaccountsof scientific explanation do not run up agai'st the problem of irrelevance.

It is easyto criticize Hempel for failing to respectthe close link bctween causality and explanatio.r, urri _ur*O"opt";;;;;;;

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In some ways, this criticism is a bit unfair. For Hempel subscribed to a philosophical doctrine known as empiricism,and'empiricists are traditionally very suspiciousof the concept of causality. Empiricism saysthat all our knowledge comesfrom experience. David Hume, whom we met in the last chapter, was aleading empiricist, and he argued that it is impossible to experiencecausal relations. So he concluded that they don't exist - causality is a figment of our imagination! This is avery hardconclusion to accept' Surely it is an objective fact that dropping glassvasescausesthem to break? Hume denied this. He allowed that it is an objective fact that most glassvasesthat have been dropped have in fact broken. But our idea of causality includes more than this. It includes the idea of a causallink between the dropping and the breaking, i.e. that the former brings about the latter. No such links are to be found in the world, according to Hume: all we seeis avase being dropped, and then it breaking a moment later. We experienceno causal connection between the first event and the second.Causality is therefore a fiction.

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Most empiricists have not acceptedthis startling conclusion outright. But as a result of Hume'swork, theyhave tended to regard causality as a concept to be treated with great caution. So to an empiricist, the idea of analysing the concept of explanation in terms of the concept of causality would seem perverse.If one's goal is to clarify the concept of scientific explanation, as Hempel's was, there is little point in using notions that are equally in need of clarification themselves.And for empiricists, causality is definitely in need of philosophical clarification. So the fact that the covering law model makes no mention of causality was not a mere oversight on Hempel's part. In recent years, empiricism has declined somewhat in popularity. Furthermore, many philosophers have come to the conclusion that the concept of causality,although philosophically problematic, is indispensableto howwe understand the world. So the idea of a causality-basedaccount of scientific explanation seemsmore acceptablethan it would have done in Hempel's day. 51

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Causality-based accountsof explanationcertainly c:rpIrrrrrthr. structureof many actualscientificexplanationsqtritc r't,ll. lrrrtarr: thcy the whole story?Many philosopherssayno, on thc grorrnrls that certainscientificexplanationsdo.ot seemto bc carrs:rl. ()nc type of examplestemsfrom what are called,theorctir.ul identifications'in science.'fheoreticalidentificationsirr''I*r identifting one conceptwith another,usuallydralvn f r.onr;r c{ifferentbranch of science.'Water is HrO'is an exanrplc,:rsis 'temperatureis averagemolecularkinetic energy'.In lr.t h .l'thcsc cases'a familiar everydayconceptis equatedor iderrti{icd*,itlr a more esotericscientificconcept.often, theoretical idcrrti{ic;ttio's furnish us with what seemto be scientificexplanatio.s.whc' chemistsdiscoveredthat water is HrO, they thereby explai'etl what water is. similarly, when physicistsdiscoverecltrr.t .rr object'stemperatureis the averagekinetic energyof its r''lcculcrs, o they therebyexplainedwhat temperatureis. But ncithcr oi'these t o explanationsis causal.Being made of HrO doesn'tcu.u.s(: Lr o substanceto be water - it just fs being water. Having a Parlicrrlar G o. avcragemolecularkinetic energ'ydoesn'tcausealiq'id t' h.ve tlrt: o temperatureit does- it just zshaving that temperature.lf these = c o. cxamplesare acceptedaslegitimate scientificexplanntions.lhcy srrggestthat causality-based accountsof explanatio. ('irlrot. be tlr. 'rvholestory.

will be able to explain Many pcoplt:lxrlievctlral' in tltt: en
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everything? 3 But doesthis mean that sciencecan in principle explain o t oraretheresomephenomenathatmustforevereludescientific ) one the On to answer' questioh easy an explanation? This is not It hand, it seemsarrogant to assertthat sciencecan explain to assertthat everything.On the other hand, it stretnsshort-sighted scientifically' any particular phenomenoncan neverbe explained phenomenonthat Fbr scienccchangesand developsvery fast' and a of today's looks completely inexplicable from the vantage-point

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sciencemay be easilyexplainedtomorrow'

Modern sciencecan explain a great deal about the rv.rld rve livc i.. But there are also numerousfactsthat havenot been cxpl.i'ccr b1, science,or at leastnot explainedfully. The origin of lif'c is .ne suclr example.We know that about 4,billion yearsago,n.rol.<.rrlt,s ,,vitlr the ability to make copiesof thdmselvesappearedin the prirrev.l soup,and life evolvedfrom there. But we do not undcrstan
logical reason According to some philosophers, there is a purely For in order to why sciencewill never be able to explain everything' somethingelse' explain something,whateverit is, we needto invoke I]utwhatexplainsthesecondthing?'Ibillustrate,recallthat his law of Newton explaineda diverserange of phenomenausing asks gravity. But what explains the law of gravity itself? If someone what should uh.y allbodies exert a gravitational force on each other' In question' we tell them? Newton had no answer to this principle: Newtonian sciencethe law of gravity was a fundamental The it explainedother things, but corrld not itself be explained' 53

nloral is generalizable.However much the scienceof the firtrrrc can cxlllain, the explanationsit giveswill haveto make use r{'ccrr:rin liutcltmental.lawsand principles.Sincenothing can explai' itsclf, it folkrws that at least some of theselaws and principles will tlrcnrsclvesremain unexplained. Wh:rtcvcr one makes of this argument, it is undeniably very tbstract. It purports to show that some things will never be cxlllained,but doesnot tell us what they are. However,some philosop\ers have made concrete suggestionsabout phenonrcr.r;r that they think sciencecan never explain. An example is consciousness - the distinguishingfeature of thinking, fecli'g creaturessuch as ourselvesand other higher animals. Much researchinto the nature of consciousness has been and continue,sto be done, by brain scientists,psychologists,and others. But a l) number of recent philosophers claim that whatever this research 5 throws up, it will nevbr fully explain the nature of consciousnes.s. ,x o There is something intrinsically mysterious about the phenomenon 4 tl they maintain, that no amount of scie.tific o of consciousness, investigation € can eliminate. s

or at least one goirrgs-onin the brain. Hence consciousness, of it, is scientificallyincxplicable' inrportant a^spect Though quite compelling, this argument is verY controversial and not endorsedby all philosophers, let alone all neuroscientists. Indeed, a well-known book published in 199r by the philosopher Daniel Dennett is defiantly entitled consciousnessEtptained. Srrpportersof the view that consciousnessis scientifically inexplicable are sometimes accusedof having a lack of imagination. Even if it is true that brain scienceas currently practised cannot explain the subjective aspectofconscious experience,can we not irrraginethe emergenceof a radically different type of brain science, with radically different explanatory techniques, thatdnes explain n4ry our experiencesfeel the way they do? There is a long tradition ol philosophers trying to tell scientists what is and isnt possible, arrd later scientific developmentshave often proved the philosophers wrong. only time will tell whether the same fate arvaitsthose who argue that consciousnessmust always elude

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What are the grounds for this view? The basic argument is that consciousexperiencesare fundamentallyunlike anything clsc in the world, in that they havea'subjectiveaspect'.Consider,for exanrple, the experienceof watching a terrifying horror movie. This is it. experiencewith a very distinctive'feel'to iu in the currentlarg,rn, there is'something that it is like'to havethe experience. Neuroscientistsmay one day be able to give a detailed account of the complexgoings-onin the brain that produceour feeling of terror. But will this explain why watching a horror movic fi:cls the way it does,rather than feeling some other way? Many people believethat it will not. on this view, the scientific study of the brain can at most tell us which brain processesare correlated with which consciousexperiences.This is certainly interesting and valuable information. However, it doesnt tell us uhy experienceswith disti nctive subjective'feels' should result from the purely ph-vsi cal

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andreduction Explanation 't'lre different scientific disciplines are designedfor explaining rlifferent types of phenomena. To explain why rubber doesn't 'lb srnduct electricity is a task for physics. explain why turtles have such long lives is a task for biology. To explain why higher interest r6tes reduce inflation is a task for economics,and so on' In short, there is a division of labour between the different sciences:each specializesin explaining its own particular set of phenomena. This r:xplainswhy the sciencesare not usually in competition with one another - why biologistq*for example, do not worry that physicists irnd economists might encroach on their turf. Nonetheless,it is widely held that the different branches of science are not all on a par: some are more fundamental than others' physics is usually regarded as the most fundamental scienceof all. 55

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Why? Becausethe objects studied by the other sciencesarc ultimately composedof physical particles. Consider living organisms,for example.Living organismsare made rrp of cells, which are themselvesmade up of water, nucleic acitls (strdr as DNA), proteins,sugars,and lipids (fats), all of which consistof moleculesor long chainsof moleculesjoined together.Ilut moleculesare made up of atoms, which are physical particles. So the objects biologists study are ultimately just very cornplex physical entities. The same applies to the other sciences,evernthe socialsciences.Thkeeconomics,for example.Economicsstudiestlre behaviour of corporations and consumersin the market place, and the consequencesof this behaviour. But consumersare hunran beingsand corporationsare made up of human beings; and hurrran beings are living organisms,hence physical entities.

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Does this mean that, in principle, physicscan subsumc all the higher-level sciences?Since everything is made up of physical particles, surely if we had a complete physics,which allou,r,:rlus to predilt perfectly the behaviour of every physical parricle in the universe,all the other scienceswould becomesuperflrrous?Most philosophers resist this line of thought. After all, it secnrscr:rzyto suggestthat physicsmight one daybe ableto explain tlrc Llrirrgsthat biology and economicsexplain.'fhe prospectof cleducingtlrc laws of biolory and economicsstraight from the laws of plrysicslooks very remote. Whatever the physics of the future looks like, it is most unlikely to be capableof predicting economicdownttrr's. I.ar fi'orrr being reducible to physics,sciencessuch as biology ancl cc:'n'rnics seemlargely autonomous of it. This leads to a philosophical puzzle.How can a sciencethat studics entities that are ultimately physical notbe reducible to phl,sics? Granted that the higher-level sciencesare in fact auto'o'ous of physics,how is this posSible?According to somephilosophcrs,the answer lies in the fact that the objects studied by the highcr-level sciencesare'multiply realized'at the physicallevel.To illustr.a.te the idea of muitiple realization, imagine a collection of ashtrays. l-iach

entity' like everything else intliviclual ruslttrayis obviously a physical of the ashtrayscould in the universc.llut the physicalcomposition of glass' others of be very cliffcrcnt - sonrc might be made and so on' And theywill probably aluminium, others of pla^stic, is virtually no limit on the differ in size, shape,nirrl weight"l'hcre that an ashtray can have' So it range of difl'erent physical propertitts in purely physical is iripossible to deline thc conccpt'a'slrtray' of the form'x is an ashtray if terms. We cannot find a true statemelrt is Iilled by an expressiontaken and only if x is . . . .'where the blank that ashtrays are multiply from the language of physics' This mcans realized at the PhYsicallevel' Philosophershaveofteninvokedmultiplerealizationtoexplainwhy chemistry but in psychologycannot be reduced to physics or science' prirr"ipt" it e explanation works for any higher-lwel that nerve cells live t:"q"t Consider,for example,the biological fact { so one might think that than skin cells. Cells are physical entities' i g However' cells are physics' by q
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Scientificrealismand anti-realism

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r;r;xrsirrgschoolsof thought calredrearism anditleor.i.snr. Irearisr' lrrlds that the physicalworrd existsindependently'f htrrrr.n th'ught :rnd perception.Idealism deniesthis it - cr.ir.s t.rratthc plrysicalworld is in someway dependenton the c'nsci'rs actir"itv o['humans.To most people,realism seemsmore plausible than idcalism.For realism fits welr with the common-sense vier.r,that t'hcfacts about the world are'out there'waiting to be criscovered by us, but idealismdoesnot. Indeed.,at first glanceidearism can sound plain silly.since rocks and treeswould presumabrl, c'ntinue to exist evenif the human race died out, in what senseis thcir cxistencedependenton human minds? In fact, the isstreis a bit more subtle than this, and continues to be discussed by philosopherstoday.

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Though the traditional realism/idealismissue berongsto an area of philosophycalledmetaphgsics,it has actually got nothing in particular to do with science.our concernin this ch.pter is with a more modern debatethat is specificallyabout science,a'rl is i' somewaysanalogousto the traditional issue.The dcbateis betwcen a position known as scienffic realismand its converse, knorvn as anti-realism or instramentarisnz.From now on, we srralrusethe word'realism' to mean scientificrealism,and'realist' to'rcan scientificrealist. 58

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Like most philosophical'isms',scientificrealism comesin many But different versions, so cannot be defined in a totally precise way' the basic idea is straightforwot.l. @ sound scienceis to provide a true descriptionof the world' This may is tit u r.irty innocuous doctrine. For surely no-one thinks science " aimingtoproduceafalsedescriptionoftheworld.Butthatisnot aim of what anti-realists think. Rather, anti-realists hold that the the of part scienceis to provide a true description of a certain of world - the'observable' part. As far as the'unobsenable'part true is says the world goes,it makes no odds whether what science or not, according to anti-realists.

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i Whatexactlydoanti-realistsmeanbytheobservablepartofthe , 8 world? They mean the everydayworld of tables and chairs' trees and and animals,test-tubesand Bunsenburners,thunderstorms 3 A snow showers, and so on. Things such as these can be directly a 5 perceivedby human beings - that is what it means to call them 4 1l a observable.Some branches of sciencedeal exclusivelywith objects of study that are observable.An example is palaeontology' or the fossils. Fossilsare readily observable- anyone with normally functioning eyesightcan seethem. But other sciencesmake claims about the unobservableregion of reality' Physicsis the obvious example. Physicistsadvancetheories about atoms, electrons' be quarks, leptons, and other strange particles, none of which can Iie observedin the normal senseof the word. Entities of this sort beyond the reach of the observational powers of humans'

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with respectto scienceslike palaeontology,realists and anti-realists that do not disagree.since fossils are observable,the realist thesis thesis scienceaims to truly describe the world and the anti-realist obviously that scienceaims to truly describe the observableworld it coincide, as far as the study of fossils is concerned' But when comesto scienceslike physics, realists and anti-realists disagree. Realists say that when physicists put forward theories about

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What do antirealists think physicists are up to when thg'talk unobservableentities? Typically they claim that thcsc entities "biltt are merely convenientfictions, introduced by physicistsirr ordcr to help predict observablephenomena.To illustrate, consirk:rthe kinetic theory of gases,which saysthat any volunrc ol'a gas<xrntrtins a large number ofvery small entities in motion. Thcse eutitics molecules - are unobservable.From the kinetic thcor.y wc (:an deducevarious consequences about the observablcbehtviour of gases,e.g.thatheating a sampleof gaswill causeit to cxparrclif the IU pressureremains constant, which can be verified experinrcntally. c o According to anti-realists, the only purpose of positing o unobservableentities in the kinetic theory is to dedrrcc s c consequences of this sort. Whether or not gasesreally c/ocolrtain o moleculesin motion doesn'tmatter; the point of thc kinctic thcory € a o is not to truly describethe hidden facts, but just to provi
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Muchofthemotivationforanti-realismstemsfromthebeliefthat the unobservable part of we cannot actually attain knowledge of this view' the limits to reality - it lies beyond human ken' On powers of observation' So scientific knowledge are set by our trees, and sugar crystals' sciencecan give uJkrro*le4ge of I'ossils, quarks - for the latter are but not of atoms, electrons, and unobservable.Thisviewisnotaltogetherimplausible.Forno-one coulrlseriouslydoubttheexistenceoffossilsandtrees,butthesame we saw in the last chapter' in t is not true of atoms and electrons' As I did doubt the the late l$th century many leading scientists such aview must obviously l existenceof atoms' Anyone who accepts t o theories about i give some explanation of whg scientists advance I I unobservableentities,ifscientificknowledgeislimitedtowhatcan are they 9. that is give be observed.The explanation anti-realists things of predict the behaviour convenient fictions,iesigned to hclp in the observableworld' J

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Realistsdonotagreethatscienti{icknowledgeislimitedbyour believe we already powers of observation' On the contrary they

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havesubstantialknowledgeofunobservablereality.Forthereis everyreasontobelievethatourhestscientifictheoriesaretrue,and entities' our best scientific theories talk about unobservable '. ' example, the atomic theory of matter' which saysthat Consider'tor theory is capable of tt matter is made up of atoms"I'he atomic the world' According to explaining a great range of facts about

is true' i'e' that matter ."ulir*, that is goodwid"nce that the theory theorysays'Of course reallyis madeup of atomsthat behaveasthe evidencein its the theory migitbefalse, despitethe apparent atomsare favour,but so might anytheory'Justbecause as that is no reasonto interpret atomictheory unobservable, 61

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strictry we should distinguish two sorts of anti-rearisrn. Accor
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otherwise'But we w'l never k"o*;h-i;h^ays the anti-rearist. so tlre correctattitudetowards the claimsthat scientistsmake abour y:lr"Trbre reality,isoneof totaragnosticism. Theyareeithertrue or false,but we areincapable of finding ooi *rri"fr. Uost mn.lerrl anti-realismis of this second sort.

The'nomiracles' argument Many theories that posit unobservableentities are enipitica.tt,tl succesqfur- they make excellent predictions about trre behaviour of objects in the observable world. ifr" lrr",i" theory of gases, mentioned above,is one example, and there are many others. Furthermore, such th

apprications.r".".J;;::i::1,:ffi H",HI*"#:h-j* abormwhat happenswhen electr"",

i;-";om go from lrigher to lower energy-states'And lasers*o* ],t us to correct our vision, attack our enemies ", "rro* with guided _irrit"r, and do nruclr more The theoqy'that underpins laser technology is therefore P:r:l*. highly empirically successful.

The empirical successof theories that posit unobservableentities is the basis of one of the strongest arguments for scientific realism, calledthe'no miracles'argument.According to this argument, it would be an extraordinary coincidence if a theory that talks about electrons and atoms made accurate'predictions about the observableworld - unless electrons and atoms actually exist. If there are no atoms and electrons,what explains the theory's close fit with the observational data? Similarly, how do we explain the technological advancesour theories haveled to, unlessby supposing that the theories in question are true? If atoms and electrons are just'convenient fictions', as anti-realists maintain, then why do laserswork? On this view, being an anti-realist is akin to believing in miracles. Since it is obviously better not to believe in miracles if a non-miraculous alternative is available,we should be realists not anti-realists. a n J

This argument is not intended to proaethat realism is right and anti-realism rilrong. Rather it is a plausibility argument - an inference to the best explanation. The phenomenon to be explained is the fact that many theories that pnstulate unobservable entities enjoy a high level of empirical success.The best explanation of this fact, sayadvocatesof the'no miracles'argument,is that the theories are true - the entities in question really exist, and behavejust as the theories say.Unless we accept this explanation, the empirical successof our theories is an unexplained mystery. Anti-realists have respondedto the'no miracles'argumentin various ways. One responseappealsto certain facts about the history of science.Historically, there are many casesof theories that we now believe to be false but that were empirically quite successful in their day. In a well-known article, the American philosopher of scienceLarry Laudan lists more than 3O such theories, drawn from a range of different scientific disciplines and eras.The phlogiston theory of combustion is one example.This theory which was widely accepteduntil the end ofthe l8th century held that when any object burns it releasesa substancecalled'phlogiston'into the

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atmosphere.Moder. chcrrrisLrytcachesus that tlri.sis {al.sc: thcre is no such substanceas phlogiston.Rather,burni.g'r:ctrrs wherr things react with oxygenin the air. Ilut despitethe non-existence of phlogiston,the phlogistontheory was empirically quiLc successful:it fitted the observational data available at tlre time reasonablywell. Examples of this sort suggestthat the'no miraclcs' .rgurnent for scientific realism is a bit too quick. proponents of that argument regard the empirical successof today's scientific theories as evidenceof their truth. But the history of sciencesh'rvs trrat empirically successfultheories have often turned out to bc farse.so how do we know that the same fate will not befail torlay's theories? How do we know that the atomic theory of matter, fbr example, will not go the same way:rs the phlogiston theory? Once we pay due o attention to the history of science,argue the anti_realists, we C see o that the inference from empirical successto theoretical truth is a o very shaky one. The rational attitude towards the atomic theory is €A thus one of agnosticism - it maybe true, or it may not. We just o do o not know, say the anti-realists. c o-

This is a powerful counter to the ,no miracles,argument, btrt it is not completely decisive.Some realists have respondedby modif,,ing the argument slightly. According to the modified version, the empirical successof a theory is evidencethat what the tlreorv savs about the unobservableworld is approximately true, rott.,", tl,u' preciselytrue- This weaker claim is lesswlnerabre to counterexamplesfrom the history of science.It is arsomore mocrest: it allows the realist to admit that today's theories may not rre correct down to every last detail, while still holding that they are broacilyon the right lines. Another way of modifring the argumcnt is by refining the notion of empirical success.some rearistshorcr that empirical successis not just a matter of fitting the known observationaldata, but raiher allowing us to predict nerv observationalphenomena that were previously unknown. Rerative to this more stringent criterion of empirical success,it is ress easyto

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successfultheories that later find historical examplesof empirically turned out to be false' savethe'no miracles' whether these refinements can rcally the number of is debatable'They certainly reduce "rgu-"nt not to zero' One that remains is historical counter-examples,but in forward by Christian Huygens the wave theory of light, first put consistsof wave-like vibrations 169o.According to this theory light ether' which was supposedto in an invisible medium called the (The rival to the wave theory was the permeatethe whole universe' that light favoured by Newton' which held iarticle theory of light, by the light source') The consistsof very small particles emitted until the French physicist wave theory was not widely accepted of the theory in Auguste Fresnelformulated a mathematicalversion surprisirrg new optical 1815,and used it to predict some

r f phenomena.OpticaiexperimentsconfirmedFresnel'spredictions' I of theory that the wave convincing many l9th-century scientists I us the theory is not tells physics light mustbe true. But modern ether, so light doesn't "o"'j':o1,-true: there is no such thing as the t but empitlcarry false a of example an have we vibrations in it. Again, t successfultheory' is that it tells against even The important feature of this example For Fresrel's the modified version of the'no miracles'argument' so qualifies as empirically theory d'id' makenovel predictions' notion of empirical success' successfuleven relative to the stricter theory can be called And it is hard to seehow Fresnel's around the idea of the 'approximately t*";, giu"t that it was based exactly it means for a theory ether, which does not exist' Whatever is surely that the to be approximately true' a necessarycondition entitiesthetheory-talksaboutreallydoexist'Inshort'Fresnel's even according tb a strict theory was empirically successful was not even approximately tru* understanding of this notion, but is that we should not The moral of the story say anti-realists' assumethatmodernscientifictheoriesareevenroughlyontheright successful' lines, just becausethey are so empirically

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Whether the'no miracles'argumentis a good argumerntfor scientilic realism is thereforean open question. on the onc hand, tlrc argument is open to quite seriousobjections, as rveh.ve seen. o' the other hand, there is somethingintuitively com'c'ing about thc argument. It realy is hard to acceptthat atoms and ercctrons might not exist,when one considersthe amazing success'f theories that postulate these entities. But as the history of scienceshows, rve should be very cautiousabout assumingthat our current scic.tific thcories are true, however well they fit the data. Many pco'lc have assumedthat in the past and been proved wrong.

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Central to the debate between realism and anti_realisrnis the distinction betqreenthings that are observable and thi.gs that are not. So far we have simply taken this distinction for grantecl _ tables.b'ndchairs are observable,atoms and erectronsare not. Ilut in fact the distinction is quite philosophicaty problematic. Indeed, one of the main arguments for scientific realism saysthat it is not possibleto draw thdobservable/unobservable distinction in a principled way. why should this b,ean argument for scientific realism? Becausethe coherenceofanti-rearism is cruciaily dependent on thcre being a clear distinction between the observableand the unobs_eruotrl". Recall that anti-realists advocatea different attitude towarcls scientific claims, depending on wrrether they are about observabre or unobservableparts of reality - we should remain agnostic about the truth of the latter, but not the former. Anti-realism thus presupposesthat we can divide scientific claims into two sorts: those that are about observableentities and prgcesses,and those that are not. If it turns out that this division cannot be made in a satisfactory way, then anti-realism is obviously in serious trouble, and realism wins by default. That is why scientific rearistsare often keen to emphasizethe problemsassociated with the observable/ unobservabledistinction.

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observation and One such problem concernsthe relation between not observable in detection. Entities such as electrons are obviously theordinarysense'buttheirpresencecanbedetectedusingspecial particle piecesof apparatus called particle'cletectors'The simplest closed container ietector is the cloud chamber, which consistsof a (Figure 9)' filled with air that has been saturated with water-vapour the When charged particles such as electrons passthrough converting them chamber,they collide with neutral atoms in the air' causing liquid into ions; water vapour condensesaround these ions eye' We can droplets to form, which can be seenwith the naked by chamber follow the path of an electron through the cloud this mean that watching the tracks of these liquid droplets' Does would say electrons can be observed after all? Most philosophers observethem no: cloud chambers allow us to detect electrons' not jets can be detected by directly. In much the sameway, high-speed these trails is not the vapour trails they leavebehind, but watching observingthejet.Butisitalwaysclearhowtodistinguishobserving fromdetecting?Ifnot,thentheanti-realistpositioncouldbe in trouble. Inawell-knowndefenceofscientificrealismfromtheearlylg6os' following the American philosopher Grover Maxwell posed the of problem for the anti-realist' Consi
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i.t these than observing?'thereis no principled way of answering to questions,Maxwell argued, so the anti-realist's attempt is doomed to ctassi$,entities as either observableor unobservable failure. Maxwell's argument is bolstered by the fact that scientists with the help themselvessometimes talk about'observinglparticles literature' of sophistieatedbits of apparatus. In the philosophical unobsen'rable of electrons are usually taken as paradigm examples entities, but scientists are often perfectly happy to talk about ,observing'electrons using particle detectors. of course,this does are not prove that the philosophers are wrong and that electrons regarded observableafter all, for the scientists'talk is probably best about as afogon-d'e-parler.Similarly, the fact that scientists talk having'experimental proof of a theory does not mean that in experiments can really prove theories to be true' as we saw Chapter 2. Nonetheless,if there really is a philosophically importantobservable/unobservabledistinction,asanti-realisls way maintain, it is odd that it correspondsso badly with the scientists themselvessPeak. Ma,rwell's arguments are powerful, but by no means completely decisive.Bas van Fraassen,a leading contemporary anti-realist' be a claims that Ma:rwell's arguments only show'observable'to

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va8ueconcept.Avagueconceptisonethathasborderlinecases. it.'Bald'is casesthat neither clearly do nor clearly do not fall under are there an obvious example. Since hairloss comes in degpes' not' many men of whom it's hard to say whether they are bald or perfectly But van Fraassen points out that vague concepts are 9. q": of the firstphotographs to showthe tracks ofsubatonric particles in a cloud challgr. The picture was taken ty tt,. cha'rber's inventor, English physi"i.t C. i "1.r,,,1 n. Wilson, at thc Cavenaish Laboratory in Cambridge in isir. The tracks are due i" ufpn. p,"i"L"" emitted by a small amount ofradinm on thelop of a metai ,,rrri ,* inserted into the cloud chamber. As an electrically ch."g*a f.ii"f ., through the rvater vapour in a cloud chamber, it in,,il"* , ir"'g*r, 'loves o* and water drops condenseon the ion., thus producing a |.rackof - rdroplets where the particle ha passed.

usable,andcanmarkgenuinedistinctionsintheworld.(Infact, would most conceptsare vague to at least some extent') No-one is unreal or men argue that the distinction between bald and hirsute unimportantsimplybecausebald'isvague'Certainly'ifweattempt todrawasharpdividinglinebetweenbaldandhirsutemen,itwill bald arbitrary. But since there are clear-cut casesof men who are drawing and clear-cut casesof men who are not' the impossibility of

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sharp dividing line doesnt matter.The conceptis l clcspiteits vagueness. 'erf'ectry's.rrre

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Preciselythe same applies to .observable,, according to van liraassen'There are crear-cutcases ofentities that can be f
argument Theunderdetermination One argument for anti-realism centres on the relationship between scientists'observational data and their theoretical claims. Antirealists emphasizethat the ultimate data to which scientific theories are responsibleis always observational in character. (Many realists would agreewith this claim.) To illustrate, consider again the kinetic theory of gases,which saysthat any sample of gas consistsof molecules in motion. Since these molecules are unobservable,we obviously cannot test the theory by directly observing various samplesof gas. Rather, we need to deduce from the theory some statement that can be directly tested, which will invariably be ahorrt observableentities. As we saw,the kinetic theory implies that a sampleof gaswill expandwhen hr:ated,if the pressureremains constant. This statement can be directly tested, by observing tht: readingson the relevantpiecesofapparatus in a laboratory (ltigttre ro). This exampleillustratesa generaltruth: observationaldata

I lrw strong an argument is this? Van Fraassenis certainly right that .ltc existenceof borderline cases,and the consequentirnpossibirity ,l''rawing a sharp boundary without arbitrariness, docs n't sh'rv thc obscrvable/unobservabledistinction to be unrear. Tb that ttxtt:'t, his argument against Maxwell succeeds.However, it is one thing to showthat there is a real distinction betweenobscrvableand tutrrbservable entities,and another to show that the distinction is crtpableof bearing the philosophical weight that anti-rcalists wis' tr place on it. Recall that anti-rearists advocatean attituclc of tnmplete agnosticism towards craims about the unobseruablepart of reality - we have no way of knowing whether they are true or not, they say'Even if we grant van Fraassen his point that there arc clear casesofunobservable entities, and that that is enough for the antirealist to be getting on with, the anti-realist still needsto provide an argument for thinking that knowredge of unobservabrerearity is impossible. lo. Dialatometer for measuring the change in volume of a gas as its temperature varies.

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constitutethe ultimate evidencelbr claims about truobscrvablc entities. Anti-realists then argue that the observational data 'unaeraetermtne' . What doesthis mean? I!g@u$_Lhat the data can in Principle be

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the caseof the kinetic theory anti-realistswill sayth:rt r;n. possible explanation of the observational data is that gasescontairr large numbersof moleculesin motion, asthe kinetic theory says.llut they will insist that there are other possible explanations to., r,vhich conflict with the kinetic theory. So according to anti-realists, scientific theories that posit unobservableentities arc underdetermined by the observational data - there rvill ahvaysbc a number of competing theories that can account for that data equalJywell.

It is easyto seewhy the underdeterminationargumc.t s.1'rprrtsan anti-realist view of science.For if theories are always underdetermined by the observational data, how can wc cvur ha'r-' = s Areasonto believethat a particular theory is true? supposca.scicntist advocatesa given theory about unobservableentities, on tlrt: groundsthat it can explain a large range of observati.na.lclata.Arr anti-realistphilosopherof sciencecomesalong,and .rgrres that the data can in fact be accountedfor by various alternative the'ries. If the anti-realistis correct,it follows that the scientist'seonfidencein her theory is misplaced.For what reasondoesthe scientistrravet' choosethe theory she does,rather than one of the altern;rtives?ln such a situation, surelythe scientistshould admit that shc lras no ideawhich theory is true? underdetermination leads n.turaily t. the anti-realistconclusionthat agnosticismis the correct attitude t
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But is it actually true that a given set of observational clatacan alwaysbe explained by many different theories, as anti-realists maintain? Realistsusually respondto the underdetennilrati'n 72

and argunrentby insisting that this clairn is true only in a trivial than uninterestingsense.In principlc, there will alwaysbe more saythe But' one possibleexplanationofa given set ofobservations' are realists,it doesnot follow that all of thesepossibleexplanations account as good as one another. Just becausetwo theories can both to nothing is there for our observationaldata doesnot mean that choosebetwcenthem. For one of the theoriesmight be simpler than the other, for example,or might explain the data in a more intuitivcly plausible way, or miglrt postulate fewer hidden causes' and so on. once we acknowledge that there are criteria for thcory the choicein aclditionto compatibility with the observationaldatiq problem of unclerdeterminationdisappears'Not all the possible explanationsof our observationaldata are .|s good as one anollttrr. lx' Even if the data that the kinetic thcory explainsciln in principlt' explained by alternative theories, it does not follow that thesc alternatives can explain as well as the kinetic theory does' 'l-his responseto the underdetermination argument is bolstercrlby the fnct that there are relatively lbrv real casesof rrndertlcterrninationin the history of science,If the observatiottal data can alwaysbc explainedequally well by many different thcories,as anti-realistsmaintaitr, surely we should expectt
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such as simplicity can be usedto adjudicatebetweencorlpcling theories immediately invites the awkward cluestionof rvh1,sirnpler theoriesshould be thought more likely to be true; we touched on this issuein Chapter 2. Anti-realists typically grant that tlre problem of underdetermination can be eliminated in practice by using criteria such as simplicity to discriminatebetweenconrpcting explanationsofour observational data. But they deny that such criteria are reliable indicators of the truth. Simpler theories n-raybe lnore convenient to work with, but they are not intrinsically more probablethan complexones.So the underdeterminationiu.gument stands: there are always multiple explanations of our dnta, u'e have no way of knowing which is true, so knowledge of unobservable reality cannot be had.

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this He cites various piecesof observational,data to support show a large hypothesis,e.g.that satellite pictures of the moon data can in crater that wasn't there before 1987' However' this perhaps a principle be explained by many alternative hypothesesOr perhaps volcanic eruption causedthe crater, br an earthquake' there is no and the camerathat took the satellite pictures was faulty, by the crater at all. So the scientist,shypothesis is underdetermined observable data, even though the hypothesis is about a perfectly the apply event - a meteorite striking the moon' If we we are underdetermination argument consistently,say realists' things of forced to conclude that we can only acquire knowledge that have actuallYbeen observed'

However,the story does not end here; there is a further realist comeback.Realistsaccuseanti-realists of applying the underdetermination argument selectively.If the argument is applied consistently,it rules out not only knowledge of the unobservableworld, but also knowledge of much of the observable world, saythe realists.To understand why realists say this, notice that many things that are observablenever actually get observed. Iior example,the vast majority of living organisms on the planet never get observedby humans, but they are clearly obscrvable.Or think of an event such as a large meteorite hitting the earth. No-one has ever witnessed such an event, but it is clearly observ4ble.lt iust so happensthat no human was ever in the right place at the right time. Only a small fraction of what is observableactually gets observed.

that any This conclusion is very implausible, and is not one of what philosopher of sciencewould wish to accept' For much observed scientists tell us concernsthings that have not been like' To say t think of ice ages,dinosaurs, continental drift' and the a that most AI say to is impossible is unobserved the of that knowledge I knowledge at of what passesfor scientific knowledge is not really all. Of course, scientific realists do not accept this conclusion' 3 Rather, they take it as evidencethat the underdetermination give us argument must be wrong. Since scienceclearly does knowledgeoftheunobserved,despitethefactthattheoriesabout that the unobserved are underdetermined by our data, it follows fact that our underdetermination is no barrier to knowledge' So the by our theories about the unobservableare also underdetermined the of data does not mean that sciencecannot give us knowledge unobservableregion of the world'

The key point is this. Anti-realists claim that the unobservahlepart of realitylies beyond the limits of scientific knowledge. So thcy allow that we can have knowledge of objects and eventsthat are observablebut unobserved. But theories about unobserued olrjects and eventsare just as underdetermined by our data as are theories about unobservableones.For example,supposea scientistputs forward the hypothesisthat a meteorite struck the moon in I.987.

the problem In effect, realists who argue this way are saying that a raised by the underdetermination argument is simply that a say To sophisticated version of the problem of induction' there are theory is underdetermined by the data is to saythat But this is alternative theories that can account for the same data' the effectivelyjust to say that the data do not entail the theory: inferencefromthedatatothetheoryisnon-deductive.Whetherthe

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thcory is about unobservableentities,or about obsen able l'rt unobservedentities,makesno difference- the logic of trrc sit.tr;rti'r is the same in both cases.Of cour.se,showing that the underdeterminationargument isiust a version of the problernof i'duction doesnot mean that it can be ignored. For trrerc is rittle consensuson howthe problem ofinduction shourd be tncklcrl,as we saw in Chapter 2. But it doesmean that there is no s1tt<:iril difliculty about unobservabree'tities. Therefore the anti-rcarist position is ultimately arbitrary saythe realists. whatcver pr.rbrenrs thcre are in understanding how sciencecan give us knorvletlge of ittoms and electrons are equally problems for understarrtliug horv sciencecan give us knowledgeof ordinary medium_sizcd obiccts.

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5 Clrapter Scientificchangeand scientificrevolutions

Scientific ideas change fast. Pick virtually any scientific discipline you like, and you can be sure that the prwalent theories in that discipline will be very different from those of 50 years ago, and extremely different from those of too yeani ago. Compared with other areasof intellectual endeavour such as philosophy and the arts, seienceis a rapidly changing activity. A number of interesting philosophical questions centre on the issue of scientific change.Is there a discernible pattern to the way scientific ideas change over time? When scientists abandon tlreir existing theory in favour of a new one, how should we explain this? Are later scientific theories objectively better than earlier ones?Or does the concept of objectivity make sense at all? Most modern discussion of these questions takes ofrfrom the work of the late Thomas Kuhn, an American historian and philosopher of science.In 1963 Kuhn published a book called TheStrumne of scientific Rersolutioru,unquestionably the most influential work of philosophy of sciencein the last 50 years.The impact of Kuhn's ideas has also been felt in other academic disciplines such as sociology and anthropology, and in the general intellectual culture at large. (The Guardiaz newspaper included The Sbtrcture of Scientific Reaolutioru in its list of the lOO most influential books of the 2oth century.) In order to understand why Kuhn's ideas caused

srlch a stir, we need to look briefly at the state of philosophy ol' st:icnceprior to the publication of his book.

science.This

liffi*tion'.

Logicalpositivistphilosophy of science

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'l'hc dorninant philosophicalmovementin the English-speaking world in the post-war period was logical positirsism.The origi.al krgical positivists were a loosely knit group of philosophers ancl scicntistswho met in Vienna in the l92os and early lggos, under the lcadershipof Moritz Schlick.(Carl Hempel,whom we met in chapter 3, was closelyassociatedwith the positivists, as was Karl Itrppcr.) Fleeing persecution by the Nazis, most of the positivists cmigrated to the united states, where they and their followers exeftcd a powerful influence on academicphilosophy until about the rnid-lg6Os,by which time the movementhad begun tcr clisintcgrate. 'l'he logical positivists had a very high regard for the natural sciences,and also for mathematics and logic. The early years of the 2oth centurywitnessed exciting scientific a.dvances, particularly in physics,which impressedthe positivists tremendously. one of their aims was to make philosophy itself more'scientific', in the rrolrcthat this woul( allow similar advancesto be made in philosoplry. what particularly impressedthe positivists about sciencewas ils app.rcnt objectivity. Unlike in other fields, where much turned on the subjectiveopinion ofenquirers, scientificquestionscould be scrtled in a fully?bjective way, they believed.Techniquessuch as experimental testing allowed a scientist to compare his theory directly with the facts, and thus reach an informed, unbiased decision about the theofofs merits. Sciencefor the positivists was thus a paradigmatically rational activity, the surest route to tlre truth that there is. Dcspitethe high csteemin which they held science,the positi'ists ltaid littlc tttcntion to tlrc history of science.Indeed,they belio,cd that philosophcrsharl littlc to lcarn f'rom studyinghistory of

and the'context

Thecontextof discovery:"ftt:-t:i:311

p..*ss by which a scientist arrives at a given theory' htrtttt*l whieh the The context ofjustification refers to the means by there - which scientist tries to justifo his theory once it is already and includes testing the theory searching for relevant evidence' subjective' so on. The positivists believed that the former was a rules' precise by psychologicalprocessthat wasnt governed of while the latter was an objective matter of logic. Philosophers they latter, the scienceshould confine themselvesto studying argued. the Belgian An example can help make this idea clearer' In 1865 has a scientist Kekule discoveredthat the benzenemolecule of a hexagonal structure. Apparently, he hit on the hypothesis he saw a hexagonalstructure for benzene after a dream in which Kekule then ,r"t trytng to bite its own tail (Figure 11)' Of course' " This is an had to test his hypothesis scientifically, which he did' can be hypotheses extreme example, but it shows that scientific always the arrived at in the most unlikely of ways - they are not productofcareful,systematicthought'Thepositivistswouldargue at initially. it,rt i makes no difference how a hypothesis is arrived Whatmattersishowitistestedonceitisalreadythere'foritis first arrived this that makes science a rational activity. How Kekule he how was at his hypothesis was immaterial; what mattered justified it. Thissharpdistinctionbetweendiscoveryandjustification,andthe the belief that the former is'subjective' and'psychological'while of philosophy to latter is not, explains why the positivists'approach processby which sciencett/asso ahistorical. For the actual historical the context of scientific ideas change and develop lies squarely in discoverynotthecontextofjustification.Thatprocessmightbeof to teach interest to historians or psychologists,but had nothing philosophers of science,according to the positivists'

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Another important theme in positivist philosophy of sciencewrs thc distinction between theories and observational facts; this is r.lated to the observable/unobservabredistinction discusseclin the l)rcvious chapter. n

lilcts, {acts,which which al+parties al could accepl.The positivists

disagreed themselvesabout how exactrythis set of neutral facts 'ctweenbe characterized, should but they were adamant that it existed. without a clear distinction between theories and observational thcts, the rationality and objectivity of science would be

compromised, and the positivistswereresorutein their beriefthat sciencewasrationaland objective.

80

Ku lr n rvasa historian of scienceby training, and firmly believed that philosophershad much to learn from studlng the historyof scir]nce.Insuflicient attention to the history of sciencehad led the positivists to form an inaccurate and naive picture of the scientific entr:rprise,he maintained. As the title of his book indicates, Kuhn wa.sespeciallyinterested in scientific revolutions - periods of great trpheavalwhen existing scientific ideas are replacedwith radicdly ne\\'ones. Examples of scientific revolutions are the Copernican revolution in astronomy,the Einsteinian revolution in physics, and thc Darwinian revolution in biolog5l.Each of these revolutions led to l fundamental change in the scientific world-view - the ovcrthrow of an existing set of ideas by a cnmpletely difrerent set. of course,scientific revolutions happen relatively infrequently most of the time any given scienceis not in a state of revolution. Kuhn coinedthe term'normal science'todescribethe ordinary dayto-rlay activities that scientists engagein when their discipline is not un
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what exactly does normal scienceinvolve?According to Kuhn it is grrirnarilya matter of puzzle-solaing. However successfula ptruligm is, it will always encounter certain problems _ phcnonrcnathat it cannot easily accommotlate, mismatches the theory's predictions and the experimental facts, and so 'ctwcenjob of the normar on.'l'he scientistis to try to eliminate theseminor puzzleswhile making as few changesas possible to the paradigm. s' uormal scienceis a highry conservativeactivity - its practitioners arc tryrng to make any earth-shattering discoveries, but rather just 'ot to develop and extend the existing paradigm. In Kuh''s words, 'normal sciencedoesnot aim at novelties of fact or theorl,, and when successfulfinds none'. Above all, Kuhn stressed that normal scientistsare not trylng to test the paradigm. On the contrary they acceptthe paradigm unquestioningly, and conduct their research within the limits it sets.If a normal scientist gets an experinrentar result that conflicts with the paradigm, she will usually assumethat her experimental technique is faulty, not that the paradigm is wrong. The paradigm itself is not negotiable. [pically' a period of norma] sciencelasts many decades,sometimes cven c'rturies. During this time scientists graduaily articulate the paradigm - fine-tuning it, filling in details, solving more ancl more puzzles,extending its range of application, and so on. But over time anomalies are discoVered- phenomena that simply cannot be reconciledwith the theoretical assumptions of the paradigm, however hard normal scientiststry. When anomalies are few in number they tend to just get ignored. But as more ancl more anomaliesaccumulate,a burgeoning senseof crisis envelopsthe scientific community. Confidencein the existing paradigrrrbreaks down, and the processof normal sciencetemporarily gri'rls to a halt' This marks the beginning of a period of 'revolutionary science, as Kuhn calls it. During such periods, fundamental scientific ideas are up for grabs.A variety of alternatives to the old paradigm are proposed,and eventually a new paradigm becomesestablished.A generation or so is usually required before all members of the scientific community are won over to the new paradigm _ an event 82 a-+.

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that marks the completion of a scientific revolution. The essenceof a scientific revolution is thus the shift from an old paradigm to a new one. Kuhn's characterization of the history of scienceas long periods of normal sciencepunctuated by occasionalscientific revolutions struck a chord with many philosophers and historians of science.A number of examplesfrom the history of sciencefit Kuhn's model quite well. When we examine the transition from PDolemaicto Copernican astronomy, for example, or from Newtonian to Einsteinian physics,many of the features that Kuhn describesare present. Ptolemaic astronomers did indeed share a paradigm, based around the theory that the earth is stationary at the centre ofthe universe,which formed the unquestioned back-drop to their investigations.The same is true of Newtonian physicists in the fSth and 19th centuries, whose paradigm was based around Newton's theory of mechanics and gravitation. And in both ciases,Kuhn's account ofhow an old paradigm gets replacedby a new one applies fairly accurately.There are also scientific revolutions that do not fit the Kuhnian model so neatly - for example the recent molecular revolution in biology. But nonetheless,most people agreethat Kuhn's description of the history of sciencecontains much of value. Why did Kuhn's ideas causesuch a storm? Becausein addition to his purely descriptive claims about the history of science,Kuhn advancedsome highly controversial philosophical theses. Ordinarily we assumethat when scientists trade their existing theory for a new one, they do so on the basis ofobjective evidence. But Kuhn argued that adopting a new paradigm involves a certain act of faith on the part of the scientist. He allowed that a scientist could have good reasonsfor abandoning an old paradigm for a new one,but hi insisted that reasonsalone could never rationally compel a paradigm shift. lfhe transfer of allegiancefrom paradigm to paradigm', Kuhn wrote,'is a conversion experiencewhich cannot be forced'. And in explaining why a new paradigm rapidly gains acceptancein the scientific community, Kuhn emphasizedthe peer

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pressureof scientistson one another. If a given paracrignrrras very forceful advocates,it is more likely to win widesprcarl acceptance. Many of Kuhn's critics were appalled by these claims. For if paradigm shifts work the way Kuhn says, it is hard to seelror.r. sciencecan be regarded as a rational activity at ail. surely scientists are meant to basetheir beliefs on evidence and reason, o. f.aith and peer pressure?Facedwith two competing 'ot paradigms, srrrelythe scientist should make an objective comparison of them to determine which has more evidencein its favour? Unclergoing a 'conversionexperience"or ailowing oneselfto be persuadcctby the most forceful of one'sfeilow scientists,hardry seemslike a rational way to behave.Kuhn's account of paradigm shifts seenrshara to reconcile with the familiar positivist image of scienceas an o objective,rational activity. one critic *"oi" g that on Kurrn,saccount, o theory choice in sciencewas .a matter for mob psychology,. J( o .E a

o Kuhn also made some controversial claims about the overall direction of scientific change.According to -e t a widely held view c scienceprogressestowards the truth in a linear fashion, as older incorrect ideas get replacedby newer, correct ones. Later theories are thus objectively better than earrier ones. This 'cumurative, conception of scienceis popular among laymen and scientists alike, but Kuhn argued that it is both historically inaccurate ancl philosophically naive. For bxample,he noted that Einstcin,s theory of relativity is in some respectsmore similar to Aristotelia' trran NerWoniantheory - so the history of mechanics is not sirnply a linear progressionfrom wrong to right. Moreover, Kuh' questioned whether the concept of objective truth actualry makes senseat at. The ideathatthere is afixed setoffactsabouttheworld, i.deperdent of any particular firadigm, was of dubious coherence,he berieved. Kuhn suggesteda radical alternative: the facts about the world are paradigm-relative, and thus change when paradigms clrange.If this sugg;estionis rigbt then it ma.kesno sense t,oask rrllet,hr: ? r*--,,:n theory eorrespondsto the facts 'as they realry are', nor tlr*."tir.* t,,

ask whether it is objectively true. Truth itself becomesrelative to a paradigm.

qndtl'te' Incommensurability of data theory-ladenness Kuhn had two main philosophical arguments for these claims' Firstly, he argued that competing paradigms are typically ,incommensurable'with one another. To understand this idea" we must remember that for Kuhn a scientist's paradigm determines her entire world-view - she views everything through the paradigm's lens. So when an existing paradigm is replacedby a new one in a scientific revolution, scientists have to abandon the whole conceptual framework which they use to make senseof the world. 3 t Indeed, Kuhn even claims, obviously somewhat metaphorically' that before and after a paradigm shift scientists'live in difrerent worlds'. Incommensurability is the idea that two paradigms may be 3 so different asto render impossible any straightforward comparison A I of them with each other - there is no common language into which o both can be translated. As a result, the proponents ofdifferent P othet's each with contact paradigms'fail to make complete

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viewpoints', Kuhn claimed.

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This is an interesting if somewhat vague idea. The doctrine of incommensurability stems largely from Kuhn's belief that scientific conceptsderive their meaning from the theory in which they play a role. So to understand Newton's concept of mass,for example, we need to understand the whole of Newtonian theory - concepts cannot be explained independently of the theories in which they are embedded.This idea, which is sometimes called'holism', was taken very seriously by Kuhn. He argued that the term'mass'actually mednt something different for Newton and Einstein, since the theories in which each embedded the term were so different. This implies that Newton and Einstein were in efrect speaking different languages,which obviously complicates the attempt to choose between their theories. If a Newtonian and an Einsteinian physicist 85

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tried to have a rational discussion,they would end up talking past each other.

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Kuhn usedthe incommensurabilitythesisboth to rcbrrt thc vierv that paradigm shifu are fully'objective',and to bolster his noncumulative picture of the history of science.Traditional philosophy of sciencesaw no huge difficulty in choosing between competing theories : you simply make an objective comparisorrof them, in the light of the available evidence,and decide which is better. Ilut this clearly presumesthat there is a common language in which both theories can be expressed.trf Kuhn is right that proponents of old and new paradigms are quite literally talking past each other, no such simplistic account of paradigm choice can be correct. Incommensurability is equally problematic for the traditional 'linear'picture of scientific history. If old and neu'paradigms are incommensurable,then it cannot be correct to think of scientific revolutionsasthe replacementof 'wrong'ideasby'right'ones. [ior to call one idea right and another wrong implies the existenceof a common framework for evaluating them, which is preciselywhat Kuhn denies.Incommensurability implies that scientific chantr1e, far from being a straightforward progression towards tlre truth, is in a sensedirectionless:Iater paradigmsare not better tlr:rn earlier olres, just different.

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Not many philosophers were convinced by Krihn's incommensurability thesis. Part of the problem wa^sthat Kuhn also claimed old and new paradigms to be incokpatible. This claim is very plausible, for if old and new paradigms were not incompatible there would be no need to choosebetween them. And in many cases the incompatibility is obvious - the Ptolemaic claim that the planets revolve around the earth is obviously incompatible with the Copernican claim that they revolve around the sun. But as Kuhn's critics were quick to point
then there is no But if the doctrine of incommensrrrability is right, Einstein here' for the actual disagreementbetween Newton and Only if the proposition meanssomething di{I'ercntfor each' i'e' only if there proporitinn has the same meaning in both theories' conflict between the i, nn in"o*mensurability, is there a genuine that Einstein's and two. Since everybody (including Kuhn) agrees reason to regard the Newton,s theories do ohflict, that is strong incommensurability thesis with suspicion' his In responseto objections of this type, Kuhn moderated that even if two incommensurability thesis somewhat' He insisted it wa^s paratligms were incommensurable, that did not mean only made impossible to compare them with each other; it different iron more difficult. Partialtranslation between of "o-pt proponenls paradigms could be achieved,Kuhn argued' so the extent: they ota ur,a new paradigms could communicate to some But Kuhn would not always be talking past each other entirely' between continued to maintain that fully objective choice paradigms was impossible' For in addition to the deriving from the lack of a common language' in"n-*"nrurability of standards" This there is also what he called'incommensurability may disagree is the idea that p?oponentsof different paradigms which about the standards for evaluating paradigms, about acceptable an what problems a good paradigm should solve, about so on' So even if solution to those problems would look like' and be able to reach they can communicate effectively, they will not Kuhn's words' ag.""*ent aboutwhose paradigm is superior' In .e-achparadigmwillbeshowntosatisffthecriteriathatitdictates

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foritselfandtofallshortofafewofthosedictatedbyitsopponent'.

argument philosophical Kuhn'ssecond ry youare thisidea'suppose data'Togras-fi asthdtheoryJadenness'of theories' The a scientist tryrng to choosebetween rwo conflicting that will decide obvious thing to do is to look for a piece of data philosophy of between the two - which is just what.traditional

sciencerecommended.Butthiswillonlybepossibleifthereexist

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why tlitl Ku'' trrink that at crata aretheory-raden? IIis writirrgs're tt't t'tdly clc'r'n this point, but at reasttwo rinesof argur,ent .re rlhrrqrniblc,'l'hc first is the idea that perceptionis heavil-y .''rllti,'cd by backgroundbeliefs- what we seedepe.ds in part ,n wlrnt w' bcricvc'so a trained scientist looking at a sopl"rist.icatecl ;tlttt:e'l'rt;rptrr*tusi' a laboratorywill seesomething cliff'erentfr'rn wlr*l rt l*yrrr*rrsccs,rbr thc scienlist obviouslyhas nrany ttlr'rrl l'lrc'p;l*r*tus trrattrrelayman racks.There arc ..11u11111gp'f 'r:riefs ;rr.yr'lr'krgicnl t:x'crimc'ts th.t supposedlyshow that perccptio' is x.lrsir'iv. i' trris w.y tr backgrouna belief - though trre crrrcct i || I *r1vp1' 1;11i1 l''r' trrcsecxpcrim ents is a contentious'r ertter. s.t'''tlly, sr:ir:rrtists' cx;rcrinrc't,r and observational reports are turrt:h.tlirr lriglrlyt'txrrcticallanguage. 'flrrrr For exarn'lc,a

electriccurrent is flowing througlr the copper rod'. But this data report is obviously laden with a lary5eamount of theory. It would not be acceptedby a scientist who did not hold standard beliefs about electric currents, so it is clearly not theory-neutral. Philosophersare divided over the merits ofthese arguments. On the one hand, many agreewith Kuhn that pure theory-neutrality is an unattainable ideal. The positivisls' idea of a classof data statements totally free of theoretical commitment is rejected by most contemporaryphilosophers- not leastbecauseno-one has succeededin sayingwhat such statementswould look like. But it is not clear that this compromises tlre objectivity of paradigm shifts t altogether. Suppose,for example, that a Ptolemaic and a o I Copernicanastronomerare engagedin a debateabout whosetheory :t is superior. In order for them to debate meaningfully, there needsto 3 a be someastrnnomicaldata they can agreeon, But why should this €t f t be a problem? Surely they can agrce about the relative position of e ro the earth and the moon on successivenights, for example,or the :l time at which the sun rises?Obviously, if the Copernican insists on tl e describing the data in a way that presumesthe truth of the 1: heliocentrictheory,the Ptolemaistwill object. But there is no 5 reilsonwhy the Copernicanshorrltldo that. Statementssuch as'on Ia May 14th the sun rose at 7.IO a.m.' can be agreed on by a scientist whether they believe the geocentric or the heliocentric theory. Such statements may not be totalftl theory-neutral, but they are sufficiently free of theoretical contamination to be acceptableto proponents of both paradigms, which is what matters. lt is cven lessobvious that the theory-ladennessof data forces us to abanclonthe concept of objective truth. Many philosophers would accept that theory-ladennessmakes it hard to seehow Imowledgeof objective truth is possible,but that is not to say that the very conceptis incoherent.Part of the problem is that, like many people who are suspicious of the concept of objective truth, Kuhn failed to articulate a viable alternative. The radical view that truth is 89

paradigm-relativeis ultimately hard to make sense of. For lihe nll such relativist doctrines,it facesa critical probrem.c.nsitlcr the question: is the claim that truth is paradigm -relative itsert'' objectively true or not? If the proponent of rerativism iurswcrs ,yes,, then they have admitted that the concept of objective t.rth rloe"s make senseand havethus contradictedthemselves.If'trrcy il'swcr 'no', then they have no grounds on which to argue witlr s'meone who disagreesand saysthat, in their opinion, truth is rrrf par.digmrelative. Not all philosophers regard this argument as completely fatal to relativism, but it does suggestthat abandoning the co'cept of objective truth is easiersaid than done. Kuhn certainly raised some telling objections to the traditional view that the history of scienceis simply a linear progression to the truth, but the relativist alternative he offered in its place is far from unproblematic. o E a,

Kuhnandthe rationality of science

Thestructure of scienffic Reaolutions is written in a very radical tone. Kuhn gives every impression of wanting to replace stanclard philosophical ideas about theory change in sciencewith € a totally G A new conception. His doctrine of paradigm shifts, of incommensurability, and of the theory-ladennessof da.* sce,'ls wholly at odds with the positivist view of scienceas a rirti''r^I, objective,and cumulative enterprise. with much justific.tir', r'ost of Kuhn's early readerstook him to be saying that scienceis an entirely non-rational activity, one characterizedby dogmatlc adherenceto a paradigm in normal periods, and sudde''conversion experiences'in revolutionary periods. o

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But Kuhn himselfwas unhappywith this interpretation of his rvork. In a Postscriptto the second edition of Thestru,cture of scien.tific Reoolutions published in t9ZO, and in subsequentwritings, Kuhn moderated his tone considerabry- and accusedsome of his early readers4f having misread his intentions. His book was not an attempt to cast doubt on the rationality of science,he arg;ued, but rather to offer a more realistic, historicaily accuratepicture of how

the scienceactually clevelops.By neglectingthe history of science' positivisls hacl been le
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o effect learn algorithms for addition, subtiaction, multiplication, 3 that t and division.) so an algorithm for theory choice is a set of rules we which tell us would when applied to twu competing theories E shoukl choose.Much positivist philosophy of seiencewas in effect I a committecl to the existenceof such an algorithm. The positivists often wrote as if, given a set of data ancltwo competing theories, the .principles of scientific method'could be used to determine which theory was superior. This idea was implicit in their belief that justification was a although discovery was a matter of psycholoSy, matter of logic.

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in Kuhn's insistencethat there is no algorithm for theory choice in scienceis almost certainly correct. For no-one has ever succeeded producing such an algorithm. Lots of philosophers and scientists h"ue m"de plausible suggestionsabout what to look for in theories But simplicity, broadnessof scope,closefit with the data and so on' as these suggestionsfall far short of providing a true algorithm, Kuhn knew well. For one thing, there may be trade-ofrs: theory one 91

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may be simpler than theory two, but theory two may fit thc rlata more closely.So an elementof subjectivejudgement, or scicnt,ific common-sense,will often be neededto decidebetwee' conrpcting thcories.Seenin this light Kuhn's suggestionthat the acloptirn of a ncw paradigm involves a certain act of faith does not secnr clrriteso radical, and likewise his emphasison the persuasiveness of a paracligm'sadvocatesin determining its chance ofwinning o'er the scicntificcommunity. 'I'hethesisthat there is no algorithm

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for theory choicele'cls support to the view that Kuhn's account of paradigm shifts is not a,nassaurt ort the rationality of science.For we can read Kuhn inste.cr as rc.jcctinga certain conception of rationality. The positivists lrclicved,in efiect,that there mustbean algorithm for trreory choice pain of scientificchangebeing irrational. This is by n, ,le*ns a 'n cr*z,yview: many paradigm casesof rational action do i'v'lver rules, or algorithms.For example,if you want to decidewhetrrcr. good is chcaper in England or Japan,you apply an algorithm for converting ltounds into yen; any other way of trying to decide the nratter is irrational. similarly, if a scientist is trying to decide betrveen two competing theories, it is tempting to think that the onry rationar woy to proceed is to apply an algorithm for theory choicc. So if.it turns out that there is no such algorithm, as seemslikely, we lrave two options. Either we can conclude that scientific change is irrational or that the positivist conception of rationality is tor_r demanding. In the Postscript Kuhn suggeststhat the latter is trre correct reading of his work.

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Kuhn'slegacy Despite their controversiarnature, Kuhn's ideas transformecl philosophy of science.In part this is becauseKuhn calleclint. qucstion many assumptionsthat had traditionally been l.ake' firr

granted, forcing philosophers to confront them, and in partbecause he drew attention to a range of issuesthat traditional philosophy of sciencehad simply ignored. After Kuhn, the idea that philosophers could afford to ignore the history of science'appearedincreasingly untenable, as did the idea of a sharp diehotomy between the contexts of discovery and justification. contemporary philosophers of sciencepay much greater attention to the historical development ofscience than did their pre-Kuhnian ancestors.Even those unsympathetic to Kuhn's more radical ideas would accept that in these respectshis influence has been positive' Another important impact of Kuhn's work was to focus attention on the social context in which sciencetakes place, something that E tE traditional philosophy of scienceignored. Sciencefor Kuhn is an t community, a scientific of existence the intrinsically social activity: bound together by allegianceto a shared paradigm, is a prerequisite for the practice of normal science'Kuhn also paid a t and A schools in taught is science how to attention considerable E scientific the into universities, how young scientists are initiated community, how scientific results are published, and other such P ,sociological'matters. Not surprisingly, Kuhn's ideas have been very c influential among sociologistsof science.In particular, a movement d J which known as the'strong programme'in the sociology of science, emerged in Britain in the 197os,owed much to Kuhn'

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The strong programme was based around the idea that science should be viewed as a product of the society in which it is practised. Strong programme sociologiststook this idea very literally: they held that scientists'beliefs were in large part socially determined. So to explain why a scientist believesa given theory for example' they would cite aspectsof the scientist's social and cultural background. The scientist's own reasonsfor believing the theory were never explanation enough, they maintained' The strong programme borrowed a number of themes from Kuhn, including the theory-ladennessof data, the view of scienceas an essentially social enterprise, and the idea that there is no algorithm for theory 93

choice.But strong programmesociologistswere nror(' ra
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Furtlrer afield, Kuhn's work has playeda role in thc rist' of tttlltt,rol relatioism in the humanities and socialsciences.Cltrllrrral relativism is not a preciselydefined doctrine,but the central idca is that there is no such thing as absolute truth - truth is always relative to :r particular culture. We may think that Western scicnce revealsthe truth about the world, but cultural relativists u'ould say that othcr culturesand societies,for exampleindigenousAnrericans,have their own truth. As we have seen,Kuhn did indeeclcnrbr:rce relativist ideas. However, there is actually a certain irrlrry in his having influenced cultural relativism. For cultur;rl relalivists are normally very anti-science.They object to the exalted status that scienceis accorded in our society,arguing that it discrirlinates against alternative belief systemsthat are equally valuable. But Kuhn himself was strongly pro-science.Like the positivists,hc regardedmodern scienceas a hugely impressivcintelkrctual achievement.His doctrine of paradigm shifts, of nornitl ancl revolutionaryscience,of incommensurabilityanclof tht'oryladennesswas not intended to undermine or criticizc the scierrtific enterprise,but rather to help us understand it bettcr.

6 Clrapter PhilosoPhicalProblems in physics,biologY' and psychologY explanation' realism' The issueswe have studied so far - induction' philosophy anrl scientific change - belong to what is called'general of scientific of science'.These issuesconcern the nature specifically to investigation in general, rather than pertaining are also many interesting chemistry say'or geolory' However, there particular sciencesphilosophical questions that are specific to the special sciences" itr"y U"iong to what is called'philosophy of 't'hesequestions usually depend partly on philosophical which is what considerations and partly on empirical facts' we examine three makes them so interesting' In this chapter and such questions' one each from physics' biology' psychologY.

LeibnizversusNewtonon absolutespace OurfirsttopicisadebatebetweenGottfriedl,eibniz(1646-17t6) outstanding scientific and Isaac Newton (16+2-1727), two of the nature ofspace and intellects ofthe l/th century concerning the the issuesabout time time. We shall focus primarily on space'but arecloselyparallel-t,,hisfu-ousPri'nciplesofNaturalPhilosophg' Newtondefencleclwhatiscalledan.absolutist'conceptionofspace. over and According to this view, spacehas an'absolute'existence Newton thought of abovethe spatial relations between objects' which God had spaceas a ihree-dimensional container into

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placedthe material universe at creation.This irnplies .'at sJra<:e existedbeforethere were any material objects,jusl. a.sa contairrur like a cerearbox existsbefore any piecesof cereala.reput inside. The only differencebetween,p""" una ordinary c.nta.inerslike cereal boxes,according to Newton, is that the latter obuirruslf havefinite dimensions,whereas spaceextendsinfinitell,in every direction. l,eibniz strongly disagreedwith the absolutist vieu, of space,a'd with much else in Newton,s philosophy. He argueclthat space consistssimply of the totarity orspaiiai rerationsbetwecnmateriar oll.jccts.llxamples of spatial relationsare.above,,.below,,.to thc lcll ol', ancl,to the right of,_ they u." ,"l"aro.rsthat matcrial bear to each other. This ,relationist, 'lljccts conception of space irrrlllicst'at beforethere were any material objects,spacedid not cxint' Leibniz arguedthat space cameinto existenceuhert Gocl creRtedthe material universe; it did not exist bef're^and, waiting t to be lilled up with material objects.So spaceis not usefully tlurught of a^sa container,nor indeed as Jn entity of any sort. l,eillniz'sview can be understood in terms of an analogv.A legal c(''tr&ct consistsof a relationship betweentwo parties - trre'rrver sctlcrof a house,for exampte. rf one ,f .h; ;;;;;",t,;;, ,i;::;'' ^r*l l,lrccontract ceasesto exist.So it would be crazy to saytha.tthc .rrrrtructruusan existenceindependentry of the rerationsrrip Irtrtwccn and se'er - the contraci;,rrt * that rer*ti'nshi'. sirnilarly,'uycr spaceis nothing over anclruou" tt spati:rirer.tions lrctwccnolrjccts. "

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N*ry.1111"'; reasonfor introducing the conceptof arrsorutes'ace 'rain wrust, distinguish betweenabsoluteand relative m'tion. Rerative nlotiolt is tlre rnotion of one object with respectto arrotlrer.. So far as *:l'tivc nrotion is concerned, it makesno senseto ask rvhether *n ,l{.ct is 'really'moving or not - we can only ask whetlrcr it is r''vi11; with rcspectto some other object.To ilrustrate,ir'aginc: two .ioggcrsrunning in tandem along a straight road. Relativeto a sli'lrrltrrstanding o' the roadside, both are,b"i".,rll- ;; ;,;;;,r 'v_ ;.

they are getting further away by tlre moment. But relative to each other, the joggers are not in motion: their relative positions remain exactlythe same,so long as they keepjogging in the same direction at the same speed.So an object may be in relative motion with respect to one thing but be stationarywith respect to another. Newton believed that as well as relative motion, there is also absolute motion. Common-sensesupports this view. For intuitively, ii doesmake senseto ask whether an object is 'really' moving or not. Imagine two objects in relative motion - say a hang-glider and an observeron the earth. Now relative motion is symmetric: just as the hang-glider is in motion relative to the observer on the earth, so the observeris in motion relative to the hang-glider. But surely it makes senseto ask whether the observer or the hang-glider is'really' moving, or both? If that is so, then we need the concept of absolute motion.

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But what exactly is absolute motion? According to Newton, it is f,: C the rnotion of an object uith respectto absolute spaceitself, o o IA Newton thought that at any time, every object has a particular :l( I t location in absolute space.Ifan ohject changesit.slocation in O.i ! absolute spacefrom one time to another then it is in absolute xJ i motion; otherwise,it is at absoluterest. So we need to think of ta spacea^san absolute entity, over and abovethe relations between material objecls, in order to distinguish relative from absolute motion. Notice that Newton's reasoning rests on an important assumption. He assumeswithout question that all motion has got to be relative to something. Relative motion is motion relative to other material objecls; absolutc motion is motion relative to absolutespaceitself. So in a sense,even absolutemotion is 'relative'for Newton. In effect, Newton is assuming that being in motion, whether absoluteor rclative,cannot be a brute fact'about an object; it can only be a fact about the object's relations to somethingelse.'I'hatsomethingelsecan either be another material object,or it can be absolutespace.

Leibniz acceptedthat there was a difference between rcl:rrive antl absolutemotion, but he denied that the latter shourrrrreexplained as motion with respect to absolute space.For he regardcclthe concept of absolute spaceas incoherent. He had a number of arguments for this view, many of which were theorogicar in nature. From a philosophical point ofview, Leibniz's most interesting argument was that absolute spaceconflicts with what he called the principle of the identity of indiscernibles(pII). Since Leibniz regarded this principle as indubitabry true, he rejected the concept ofabsolute space. PII saysthat iftwo objects are indiscernible, then they are identical, i'e' they are really one and the same object. what does it mean to call two objects indiseernible? It means that no difierence at all can be found between them - they have exactlythe same attrihtrtes. So if o PII is true, then any two genuinely distinct objects mrrst c clifl'erin at o least one of their attributes - otherwise they would be one, JI not two. o PII is intuitively quite compeiling. It certainly is not ea-syto fincl an E c example of two distinct objects that share alltheir attributes. Even Io two mass-producedfactory goods will normally E differ in t innumerable ways' even if the differencescannot be detectccrwith the naked eye.whether pII is true in general is a complex cluestion that philosophersstill debate;the answer depends part,n in exactry what counts as an'attribute,, and in part on difficult issucsin quantum physics.But our doncern for the moment is the use to which Leibniz puts the principle.

univcrse one, each object occupiesa particular location in absolute space.Inuniversetwo,eachobjecthasbeenshiftedtoadifrerent (for example). location in absolute space,two miles to the east For we There would be no way of telling these t!v'ouniverses apart. a:l space' cannot observethe position ofan object in absolute of Newton himself admitted. All we can observeare the positions objects relatioe to each othet, andthese would remain unchanged or for all objects are shifted by the same amount. No obsenrations one experiments could ever reveal whether we lived in universe or two.

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The secondthought experiment is similar. Recall that for Newton, are at some objects are moving through absolute space while others rest. This means that at each momen! every object has a definite absolute velocity. (velocity is speed in a given direction' so an object's absolute velocity is the speed at which it moves through have f ,: absolute spacein a specified direction. Objects at absolute rest an absolute velocity of zero.) Now imagine two difrerent universes' 9;i both containing exactly the same objects' In universe one' each the two' universe In object has a particular absolute velocity' iJ absolute velocity of each object has been boosted by a fixed amount" :3 say3ookilometresperhourinaspecifieddirection.Again,we .!r iii could never tell these two universesapart. For it is impossible to iii observehow fast an object is moving with respect to absolute space' as Newton himself admitted. We can only obsen'e how fast objects are moving relatioe to each other - and these relative velocities I would remain unchanged, for the velocity of wery object is boosted i could by exactly the same amount. No observations or experiments ever reveal whether we lived in universe one or two'

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Leibniz usestwo thought experiments to reveal a conflict between Newten's theory of absolute spaceand pII. His argumentative stratery is indirect: he assumesfor the sake of argument that Newton's theory is correc! then tries to show that a contradiction follows from that assumption; since contradictions cannot be true, Leibniz concludesthat Newton's theory must be farse. Recail that for Newton, at any moment in time every object in the universe bas a definite location in absorutespace.Leibniz asks us to im:rgine trvo different universes,both containing exactly the same obiects. [n

In each of thesethought experiments, Leibniz describestwo universes which by Newtods own admission we could never tell apart-theyareperfectlyindiscernible.ButbyPll,thismeansthat the two universesare actually one. so it follows that Newton's

theoryof absolutespaceis false.Anotherwayto seethe point is this. Newton'stheory impliesthat there is a genuinedifrerencebetween

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the universebeing at one location in absolute spacearrr it lr.irrg shifted to a different location.But Leibniz points rur. trrat ,ris difl'erencewould be totally undetectabl", .o lo'g as cvcr.v,lr.icct shifts location by the same rorur auluun[. amount. but But lfif no no clrtteretrce difference cart , lte detectedbetweentwo universesthen they are indiscerniblc.an,

ters *sthat they olr's theory ","J;;;ir":TJI"JJJ:,'"::ffi:T,i:l;fii::

has a falseconsequence:it implies that there are two trrirgs rvrrrr' there is only one.The conceptof absolute spacethus c:rnticts *,ith PII' The logic of Leibniz'ssecondthought experiment.is irrcrrticar.

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r2'. Newton's'rotating bucket'experirne't. In stage(i) bucket ar. water are at rest; in stage (ii) thc Lucket rotates stage (iii) bucket and water rotate in tantlem. "Jlniiou to Ur" r,ri""; i'

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Initially the water is at rest relative to the bucket. Then the rope is fwisted around a number of times and released.As it uncoils, the bucket starts rotating. At first the watet in the bucket staysstill, its surface flat; the bucket is then.rotating relative to the water. But after a few moments the bucketimparts its motion to the water, and the water begins to rotate in tandem with the bucket; the bucket and the water are then at rest relative to each other again' Experienceshowsthat the surface of the water then curves upwards at the sides,as the diagram indicates. What is causing the surface of the water to rise?, Newton asks' Clearly it is something to do with the water's rotation. But rotation is a type of motion, and for Newton an object's motion is always relative to something else.So we must ask: relative to what is the water rotating? Not relative to the bucket, obviously, for the bucket and the water are rotating in tandem and are hence at relative rest. Newton arguesthat the water is rotating relative to absolute space' and that this is causing its surface to curve upwards. So absolute spacedoes in fact have observational effects.

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E :F You may think there is an obvious gap in Newton's argument' I 5 why but bucket, the to relative rotating is not water 4 Granted the 3 The space? conclude that it must be rotating relative to absolute x, water is rotating relative to the person doing the experiment, and go so relative to the earth's surface, and relative to the fixed stars, surely any of these might be causing its surface to rise? But Newton had a simple responseto this move. Imagine a universe containing nothing except the rotating bucket. In such a universe, we cannot explain the water's curved surface by appealing to the wateCs rotation relative to other objects, for there are none' and as before the water is.at rest relative to the bucket. Absolute spaceis the only thing left for the water to be rotating relative to. So we must believe in absolute spaceon pain of being unable to explain why the water's surface curves. In effect, Newton is saying that although an objectt position in 1fil

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absolutespaceand its velocitywith respectto absrlrrtt,,',.,,,",,.r,,, never be detected,it is possibleto tell when an ob.ir..t,[ is ttt'cal.erul.irtg with respectto absolutespace.For when an object ror.atcsthe. it is by definition accelerating,even if the rate of rotation is <xrnstalrt. This is becausein physics,acceleration is defined iusthe r*tc .{' change of velocity, and velocity is speedin afi,aecr,r/irecrrirr.si.ce rotating objects are constantly changing their direction ol'motion, it follows that their velocity is not constant, hence they arc accelerating.The water's curved surface is just onc exarnplc of rvhat are called'inertial effects'- effectsproducedby accelcratcdlrrotion. Angther example is the feeling of being pushed to the b.ck of your seat that you get when an aeroplanetakes off. The only possible explanation of inertial effects,Newton believed, is the acceleration of the object experiencing those effectswith respect tr arrsolutc space.For in a universe containing only the accelerating obiect, absolute spaceis the only thing that the acceleration could be relative to.

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Nelvton's argument is powerful but not conclusive. Frlr rr'rv clocs € Newton know that the water's surface would curve upwards, if the rotating bucket experimentwas done in a universecorrtairing'o other material objects?Newton simply assumesth;rt the iner:tial effectswe find in this world would remain the same in a world bereft of any other matter. This is obviously quite a subst.antial assumption, and many people have questioned Newton's entitlement to it. So Newton's argument does not pmvc llrc existenceof absolute space.Rather, it lays down a clrallcrrgeto the defender of Leibniz to provide an alternative explarration of inertial effects. a

Leibniz also facesthe challenge of explaining the diffcrerrce between absolute and relative motion without invoking absolute space.On this problem, Leibniz wrote that a body is in true or absolute motion'when the immediate causeof the r:hangeis in the body itself. Recallthe'caseof the hang-gliderand trrc obse.er.n earth, both of whom are in motion relative to the other. 'ltr

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would saythat we need determine which is'really' movirtg, t'eibniz the change(i'e' of the to dccide whether the immetli:tte causeof observer' or both' This relative motion) is in the hang-glidex the from relative motion suggestionfor how to distinguish absolute it is not very clear' I-eibniz avoids all referenceto absolute space,but the'immediate causeof never properly explains what it mearrfor that he intended to the change'to be in an object' Ilut it may be motion' whether reject Newton's assumption that an object's the object's relations to relative or absolute, cai only be a fact about something else. One of the intriguing things about the absolute/relational account of space controversy is that it refuses to go away' Newton's and kibniz's views were was intimately bound up with his physics' that the advancer a direct reaction to Newton's' So one might think the issueby in physics since the 17th century would have resolved was once widely held now. But this has not happenc
Theproblemof biologicalclassification

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kinds' or sortingthe objectsoneis studyrnginto general Classifuing, igneous' as rocks playsa role in everyscience'Geologistsclassifr wereformed' sedimentaryor metamorphic,tlependingon howthey progressive' Economistsclassiffta.xationsystemsasproportional, dependingon how unfair they are'The main function or regressive, information.If a chemisttells you that of classificationis to "orrn.y somethingisametal,thattellsyoualotaboutitslikelybehaviour. Classificationraisessomeinterestingphilosophicalissues.Mostly' canin thesestemfrom the fact that anygivensetofobjects dassiff principlebe classifiedin manydifferentways'Chemists substancesbytheiratomicnumber,yieldingtheperiodictab-leof by their the elements.But they could equallyclassifrsubstances

urklur, or their smell,or their density.So how should we c:hoose lxrtwccn these alternative ways of classifuing?Is there a'correc:t' wty [o classifr? Or are all classificationschemesultimately nrbitrnry?'fhesequestionstake on a particular urgencyin tht: contcxt of biologicalclassification,or taxonomy,which will be our urrrccrnhere.

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lliologisl,straditionally classifrplants and organismsusing the l,itutcrn system,named after the l8th-century Swedishuaturalist Cnrl l,innacus (r7o7-r778) (Figure 13).The basicelementsof tl.re l,iuutrtu systemare straightforward, and familiar to many people. Itirst ol'rrll, individual organismsare assignedIo a species.Each rlrtrciesis tlrcn assignedlo a genus,each genusro afam,ily, each fhlrrily Io nn ordcr, each order lo a class,each classto aplrylarn, ctrtl crclr phylum to a hingdom. Various intermediate ranks, such an auln1nciu, aubfumilg, and superfamilg are also recognized. 'l'he alrccicsis the basetaxonomic unit; genuses,families, orders, tttd no on &reknown as'higher taxa'. The standard Latin name for u spccicsindicates the genus to which the speciesbelongs,but no tnorc. Iror example,you and I belong to Homo sapi.ens,the only surviving speciesin the Homo genus.T\vo of the other sgrccicsin that genus areHomo erectusand Homo habilis,botl'r ruowcxtinct. The Homo genusbelongsto the Hominid farnily. wlrirfi belongsto the Hominoid superfamily,which belongsto tlte l)rirnrtc order, which belongs to the Mammalian class,whic.lr lxrlongsto the Chordatephylum, which belongsto the Aninral kingdorn. Noticc that the Linnean way of classifinns organisms is hicrarchical:a number of speciesare nestedin a single genus,a nunrber of genusesin a singlefamily, a number of families in a singlc order, and so on. So as we move upwards, we find fewer taxa tt ca,chlevel. At the bottom there are literally millions of species, llul. tt the top there are just five kingdoms: Animals, Plants, Iiungi, llnctcria, *4rd Protoctists (algae,seaweed,etc.). Not every r:lnssilir:ntion systcmin scienceis hierarchical.The periodic table in 't04

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which he 13. Linneaus' most famotrs book Sg*tamaNaturaz'in minerals' and of planis' animals' ;ilt;;;Jft "t*rrin""iit"t

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chemistryis an exampleof a non-hierarchicalcrassific.tirn.'['he different chemical elements are not arranged into nr'rc and rn're inclusive groupings, the way speciesare in the Linnean system.one important question we must face is whgbiologicar classification should be hierarchical.

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The Linnean systemserved naturalists well for huntlreds of years, and continues to be used today. In some ways this is surprising, since biological theories have changedgreatly in that period. The cornerstone of modern biology is Darwin's theory of evolution, which saysthat contemporary specieshave descencledfrom ancestral species;this theory contrasts with the older, biblically inspired view that eachspecieswas created separatelyby God. Darwin's Origin of Specieswas published in lg59, but it was not until the middle of the 2oth century that biologists began to ask whether the theory of evolution should have any impact on the way organisms are classified.By the r97os two rival taxonomic schools had emerged,offering competing answersto this question. According ro cladists,biological classificationsshourd try to reflect the evolutionary relationships between species,so knowledge of evolutionary history is indispensablefor doing good taxonomy. According to pheneticisfs,this is not so: classification can and should be totally independent ofevolutionary considerations.A third group, known as the eaolutionary tononomists,try to combine elementsof both views. To understand the dispute between cladists and pheneticists, we must divide the problem of biological classificationinto two. Firstly, there is the problem ofhowto sort organisms into species,known as the'species problem'. This problem has by no means been solved, but in practice biologists are often able to agree about how to delimit species,though there are difficult cases.Broadly speaking, biologists assignorganisms to the same speciesif they can interbreed with each other and to different speciesotherwise. Secondly,there is the problem ofhow to arrange a group ofspecies into higher ta"xa,which obviously presumesa solution to the first 106

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problem. As it happens, cladists and pheneticists do often disagree about the speciesproblem, but their dispute primarily concerns higher ta,xa.So for the moment, we ignore the speciesproblem - we assumethat organisms have been allocated to speciesin a satisfactory way. The question is: where do we go from there? what principles do we use to classifr these speciesinto higher taxa? To focus the issue,consider the following example' Humans, chimpanzees,gorillas, bonobos, orangutans, and gibbons are usually classedtogether as members of the Hominoid superfamily. But baboons are not counted as Hominoids. why is this? what is the justification forplacinghumans, chimps, gorillas, etc' in agrcup that doesnt also contain baboons?According to pheneticists, the answer is that the former all have a number of features that baboons

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do not, for example the lack of a tail. On this view, taxonomic groupings should be based on similari.@ - they should bring f together speciesthat are similar to each other in important waln is a this Intuitively' dissimilar. are that ones out and leave reasonable view. For it fits neatly with the idea that the purpose of classification is to convey information. If taxonomic groups are based on similarity, then being told which group a particular a organism belongs to will tell you a lot about its likely characteristics. I T If you are told that a given organism belongs to the Hominoid superfamily, you will knowthat it doesnthave atail. Furtherrnore' many of the groups recognized by traditional tanonomy do seem to be similarity-based. To take an obvious example, plants all share a number of features that animals lack, so placing all the plants in one kingdom and all the animals in another makes good sensefrom the

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phenetic point of view. However, cladists insist that similarity should count for nothing in classifitation. Rather what matters are the wolutionary relationships between species - known aslhefu phylogenetic relations. Cladists agreethat the baboons should be excluded from the group that contains humans, chimps, gorillas, etc' But the justification for this has got nothing to do with the similarities and 107

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dissimilaritiesbetweenthe species.The point is ratrrcr tlr*t thc Hominoid speciesare more closelyrelatedto eacrrothcr tlr*n .rc any of thern to the baboons.what exactlydoesthis rrea'? It mcans that all of the Hominoid speciessharea common ancestorthat is not an ancestorof the baboons.Notice that this doesnol lrrcanthat the Hominoid speciesand the baboonshaveno conlrlo' . rcest()rat all. on the contrary any two specieshavea common ancr:storif'you go back far enough in evolutionary time - for all life o. carth is Prcsumedto have a singleorigin. The point is rather that tlre c(,rnmonancestorof the Hominoid speciesand the baboonsis also iltr ancestorof many other species,for examplethe various nracil(lue species.so cladistsarguethat any taxonomicgroup that c'utains tlrc Hominoid speciesand the baboonsmust also co'tain tlrese otlrer species.No taxonomicg;roupcan containju.st tltt'.IIrrnin'irl speciesand the baboons.

I,t. cladogram showingthe phylogeneticrelations betweensix contemporaryspecies.

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fanrilies, superfamilies, or whatever, must be monophalrtic. A ntonophyleticgroup is one that containsan ancestralspecicsand all ol'its dcscendants,but no-one else.Monophyleticgx)rl)s c.rne irr vitrioussizes.At one extreme,all speciesthat haveevcr cxistcrl{irrrn n rnonophyletic group,presuminglife on earthonly'rigirurte
A-F (Figure r4). All six specieshave a common ancestor if we go back far enough in time, but some are more closely related than others. species E and F have a very recent common ancestor - for their branches intersect in the quite recent past. By contra^st,epecier A split offfrom the rest of the lineage along time ago.Now consider the group {D, E, F}. This is a monophyleticgroup, since it contains all and only the descendantsof an ancestral species(not named), which split into two at the noclemarked'x'. The group {C, D, E, F} In likewise monophyletic, as is the group {8, C, D, E, F}' But the group {8, C, D, F} is not monophyletic.This is becausethe common ancestorofthese four speciesis also an ancestorofspecies ti. All thc monophyletic groups in the diagram have been ringed; any other group of speciesis not monophyletic. The dispute between cladists and pheneticists is by no means purcly academic- there are many real caseswhere they disagree' C)newellknown example concernsthe classReptilia, or the reptiles' Traditional Linnean taxonomy counts lizards and crocodiles a.q members of Reptilia, but excludesbirds, which are placed in a separateclasscalled Aves. Pheneticists agreewith this traditional

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15. cladogram showingthe phylogeneticrelationsbetwee' lizartls. crocodiles,and birds.

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classification,for birds have their own unique anatomy and physiology,which is quite different from that of lizards, croc<;clilers. and other reptiles. But cladists maintain that Reptilia is not a genuine taxonomic group at all, for it is not monophyletic. As the cladogram aboveshows,the common ancestorof the lizarcls and the crocodilesis alsoan ancestorof the birds; so placing lizarclsand crocodiles together in a group that excludesbirds violates the requirement of monophyly (Figure tb). Cladists therefbre recommendthat traditional taxonomicpracticebe abanclonc:cl: biologists should not talk about Reptilia at all, for it is an arti{icial not a natural group. This is quite a radical recommend:rtion; even biologists sympathetic to the spirit of cladism are ofter-rrelrrct.nt ro abandon the traditional taxonomic categoriesthat have icrved naturalists well for centuries. Cladistsarguethat their way of classifiiingis .objective'whilethat of the pheneticists is not. There is certainly some truth in this charge. For pheneticistsbasetheir classificationson the similarities betweeqspecies,and judgements of similarity are invariably partly subjective.Any two speiies are going to be similar to each other in somerespects,but not in others.For example,two speciesof insect might be anatomically quite similar, but very diverse in their feedinghabits. so which'respects'do we singleout, in t' 'r.der 110

make itrdgements of similarity? Pheneticistshoped to avoid this problem by defining a measure of 'overall similariqy', which would take into account all of a species'characteristics,thus permitting fully objective classificationsto be constructed. But though this idea sounds nice, it did not work, not least becausethere is no obvious way to count characteristics.Most people today believe that the very .overall similarity' is philosophically suspect.Phenetic idea of classificationsdo exist, and are used in practice, but they are not fully objective. Difierent similarity judgements lead to different phenetic classifications,and there is no obvious way to choose between them.

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Cladism facesits own set of problems. The most serious problem is that in order to construct a classification according to cladistic principles, we need to discover the phylogenetic relations between the specieswe are tryrng to classifr, and this is very far from easy' These relations are obviously not discoverablejust by looking at the t species- they have to be inferred. A variety of techniques for inferring phylogenetic relations have been dweloped, but they are not fool-proof. Intleed, as more and more evidencefrom molecular geneticsemerges,hypothesesabout the phylogenetic relations between speciesget overturned rapidly. So actually putting cladistic ideas into practice is not easy.It is all verywell to be told that only monophyletic groups of speciesare allowed in ta:
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are th us inherently conjectural. Pheneticists object that classification should not be theory-laden in this way. They maintain that taxonomy should be prior to, not dependent on, conjectures about evolutionary history. Despite the difficulty of putting cladism into practice, and despite the fact the cladists often recommend quite radical revisions of traditional taxonomic categories,more and more biologists are coming round to the cladistic viewpoint. This is mainly because 11', |

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cladismis free of ambiguity in a way that phenctic .,rl othcr approachesare not - its taxonomicprinciplesarc pr.rfi'r:r.ly clcar, evenif they are hard to implement.And there is s'rrrt:thing rluite intuitive about the idea that monophyletic groups of speciesare 'natural units', while other groups are not. Furthernr*rc, cla,dism provides a genuine rationale for why biological classificatio. should be hierarchical. As Figure 15 aboveindicates, monophyletic groups are always nested inside each other, so if the requirement of monophyly is rigidly followed the resulting classificationwill automatically be hierarchical. classifying on the basis of similarity can also yield a hierarchical cla^ssi{ication;but pheneticists have no comparablejustification fot why biological cfassification should be hierarchical. It is quite striking that naturalists have been classifyingliving organisms hierarchically for hundreds ofyears, but the true rationare for doing so has only recently become clear.

Our focus is an old but ongoing debateamong cognitive psychologistsconcerningthe architectureof the human mind' According to one view, thc httman mind is a'general-purpose problem-solver'. This mearrsthat the mind contains a set of general problem-solving skills, or''general intelligenc4 which it applies to an indefinitely large number of difrerent tasks. So one and the same set of cognitive capacities is employed, whether the human is trying to count marbles, decide whieh restaurant to eat in, or learn a foreign language - these ta.sksrepresent difrerent applications of the human's general intelligence. According to a rival view, the human mind contains a number of specializedsubsystemsor modules, each of which is designedfor performing a very limited range of tasks and cannot clo anything else (Figure 16). This is known as the mod'ularity qf mindhypothesis' So, for example' it is

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widely believed that there is a special module for language acquisition, a view deriving from the work of the linguist Noam chomsky. chomsky insisted that a child does not learn to speak by t overhearing adult conversation and then using his'general intelligence'to figure out the rules of the language being spoken; rather, there is a distinct'language acquisition device'in every human child which operatesautomatically, and whose sole function :F is to enable him or her to learn a language, given appropriate ! I prompting. Chomsky provided an array of impressive evidence for this claim - including, for example,the fast that even those with very low'general intelligence'can often learn to speak

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one of the centraljobs of psychologyis to understanclhow rruman beings manageto perform the cognitive tasks thcy do. Ily'cognitive tasks'wedo notjust mean things like solvingcrosswo*l puzzres,but also more mundane tasks like crossingthe roacl safely, understanding what other people say,recognizing other people's faces,checking one's change in a shop, and so on. There is no denying that humans are very good at many of theseta^sks- so good, indeed, that we often do them very fast, with little if any conscious thought. To appreciatejust how remarkable this is, consider the fact that no robot has ever been designedthat behaveseven remotery like a human being in a real-life situation, despiteconsiderable effort and expense.No robot can solve a crossword,or engagein a conversation,with anything like the facility the averagehuman being can. Somehowor other,we humans are capableof perf
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perfectly well. Some of the most compelling evidencefor the modularity hypothesis comes from studies of patients with brain damage' known as,deficit studies" If the human mind is a general-purpose problem-solver,we woultl expect damage to the brain to afrect all capacitiesmore or less equally. But this is not what we "ogrrftiu" find. On the contrary brain damage often impairs some cognitive capacitiesbut leavesothers untouched. For example, damage to a part of the brain known aswernicke's arealeavespatients unable to understand speech,though they are still able to produce fluent,

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gran"lmaticalsentences.'fhis strongly suggeststhat there are separatemodulesfor sentenceprexluctionand comprehension- for that would explain why loss of the latter capacity does not entail loss of the former. Other brain-damaged ilatients lose their long-term memory (amnesia),but their short-term memory and their ability to speakand understandare entirely unimpaired. Again, this seemr to speak in favour of modularity and against the view of the mind ar a general-purposeproblem-solver.

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Though compelling, neuropsychologicalevidence of this sort doet not settle the modularity issue once and for all. For one thing, tha evideneeis relatively sparse- we obviously cannot damage pooplo'r brains at will just to seehow their cognitive capacities are affectod. In addition, there are serious disagreementsabout how the data should be interpreted, as is usual in science.Some people argue thet the observedpattern of cognitive impairment in brain-damaged patients does not imply that the mind is modular. Even if the mind J were ageneral-purpose problem-solver, that is non-modular, it la still possiblethat distinct cognitive capacities might be differentially affected by brain damage,they argue. So we cannot simply'read off the architectureof the mind from deficit studiea, they maintain; at best, the latter provide fallible evideneefor the former.

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16. A hypothetical representation of a modular min
Much of the recent interest in modularity is due to the work of Jerry Fodor, an influential American philosopher and psychologist. In 1983 Fodor published a book called Thc Modularity of Mind which contained both a very clear account of what exactly a module is, and some interesting hypothesesabout which cognitive capacitiesare modular and which not. Fodor argued that mental modules have a number of distinguishing features, of which the following three are the most important: (i) they are dnmainspecific,(ii) their operation is mandatory, and (iii) they are informationally encapsulated. Non-modular cognitive systems possessnonb ofthese features. Fodor then argued that the human mind is partly, though not wholly, modular: we solve some cognitive

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tasksusing specializedmoclules,othersrrsingour ,gt.ncr.al intelligence'.

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lb saythat a cognitive system is domain-specific is tr sa' trrat it is specialized:it performs a limited, preciselycircumscribe
17' The Miiller--Lyer illusion. The horizontal lines are equar in rength, but the top one looks longer. 116

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'Iio most peopJe,the top line looks slightly longer than the bottom one. But in fact this is an optical illusion, known as the MtillerLyer illusion. The lines are actually equal in length. Various explanations have been suggest€dfor why the top line looks longer, but they need not coneern us here. The crucial point is this: the lines continue to look unequal in length, eomwhengou knou it's an optical illusion. According to Fodor, this simple fact has important implications for understanding the architecture of the mind. For it shows that the information that the two lines are equal in length is stored in a region of the cognitive mind to which our perceptual mechanisms do nothave access.This means that our perceptual mechanisms are informationally encapsulated- they do not have accessto all of the information we possess.If visual perception were not informationally encapsulatedin this way, but could make use of all the information stored in the mind, then the illusion would disappear asisoon as you were told that the lines were actually equal in length. Another possibleexample of information encapsulation comesfrom the phenomenon of human phobias. Take, for example,odiophobia, or fear of snakes.This phobia is quite widespread in humans, and also in many other primate species.This is easily understood, for snakesare very dangerousto primates, so an instinctive fear of snakescould easily have evolved by natural selection. But whatever the explanation for why we are so scaredof snakes,the crucial point is this. Even if you know that a particular snake isnt dangerous,for example becauseyou've been told that its poison glands have been removed,you are still quite likely to be terrified of the snake and will not want to touch it. Of course, this sort of phobia can often be overcomeby training, but that is a different matter. The relevant point is that the information that the snake isnt dangerous is inaccessibleto the part of your mind that produces in you the reaction of fear when you seea snake.This suggeststhat there may be an inbuilt, informationally encapsulated'fear of snakes'module in everyhuman being. 117

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You may wonder why the modularity of mind issue is at all philosophical.surely it is just a questionof empirical firr:rwlrctlrt:r the mind is modular or not, albeit not an easyone to ;.rslv<'r?Irr firct this suggestionis not quite right. One respect in.r.r,hichthe modularity debate is philosophical concernshow we sh.trlcl cour)t cognitive tasks and modules. Advocatesof modularity hol
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reasoning skills you apply here - testing for logical consistencyand assessingevidence - aregeneral skills; they are not specifically designed for use in jury service.You use the same skills in many domains. So the cognitive capacitiesyou bring to bear in deliberating the defendant's guilt are not domain-specific. Nor is their operation mandatory - you have to consciouslyconsider whether the defendant is guilty, and can stop doing so whenever you want to, e.g. during the lunch break. Most important of all, there is no information encapsulation either. Your task is to decide whether the defendant is guilty all things corui.dzred,,so you may have to draw on any of the background information that you possess,if you consider it relevant. For example, if the defendant trvitched nervously under cross-examination and you believe that nervous twitching is invariably a sign of guilt, you will probably draw on this belief in reaching your verdict. So there is no store of information which is inaccessibleto the cognitive mechanisms you employ to reach your verdict (though the judge may tell you to ignore certain things). In short, there is no module for deciding whether a defendant is guilty. You tackle this cognitive problem using your

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'general intelligence'.

= Fodor's thesis that the mind is partly though not wholly modular thus looks quite plausible. But exactly how many modules there are, and what precisely they do, are questlons that cannot be answered given the current state of research.Fodor himself is quite pessimistic about the possibility of cognitive psycholory wer explaining the workings of the human mind. He believesthat only modular systems can be studied scientifically - non-modular systems, because they are not informationally encapsulated, are much more difficult to model. So according to Fodor the best research shategy for cognitive psychologists is to focus on perception and language,ignoringthinking and reasoning. Butthis aspect of Fodor's thought is very controversial. Not all psychologists agreewith him about which bits of the mind are modular and which are not, and not all agree that only modular systems can be studied scientifically. 119

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7 Chapter Scienceand its critics

obiectionablebecauseit is inherently male-biased;those of religious persuasionoften feel that sciencethreatens their faith; and anthropologists have accusedWestern scienceof arrogance,on the grounds that it blithely assumesits superiority to the knowledge and beliefs of indigenous cultures around the world. This by no means exhauststhe list of criticisms to which sciencehas been subject, but in this chapter we confine our attention to three that are of particular philosophical interest.

Scientism Mrtuy pcopletake it for granted that scienceis a good thing, lirr obviousleixons. After all, sciencehas given us electricitl',sa{'c rlriuking watcr, penicillin, contraception,air travcl, antl uruch llrrt nlorc - tll of which have undoubtedlybenefitedl'run'rarrit_\i rvelfirre, rlcnpitcthcsc inrpressivecontributions to human scienceis rult without its critics. Somearguethat societyspenclstoo much nloncy ou scicnceat the expenseof the arts; others holclthat s<:ience Itrurgivcn us tcchuologicalcapabilitieswe would bc bcttcr ofl' witlulrrt, sur:hiusthc capacityto produceweaponsof nrass rlentructiou(ltigurc 1t|).Certain feminists arguethat scicnceis ir

The words'science'and'scientilic' have acquireda peculiar cachet in modern times. If someoneaccusesyou of behaving 'unscientifically', they are almost certainly criticizing you. Scientific conduct is sensible,rational, and praiseworthy; unscientific conduct is foolish, irrational, and worthy of contempt. It is difficult I|D to know why the label 'scientific'should have acquired these a 2 connotations, but it is probably something to do with the high A d status in which scienceis held in modern society.Society treats on regularly sought are opinions whose scientists as experts, d matters of importance and for the most part acceptedwithout question. Of course,everybodyrecognizesthat scientists sometimes get it wrong - for example, scientific advisersto the British government in the 199os declared that'mad cow disease'posed no threat to humans, only to be proved tragically mistaken- But occasionalhiccups of this sort tend not to shake the faith that the public place in science,nor the esteemin which scientists are held. In the West at least, scientists are viewed much as religious leaders used to be: possessorsof specializedknowledge that is inaccessible

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It, tfu'lertlllk'cnpnbllltler wc worrld be better offwithorrt: a.toxic ntt:ltrrxrnt r.krrrrlprrxlucrxl by nn atomic explosion.

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'scientism'is a pejorativelabel usedby some philosophersto describewhat they seeas science-worship- the over-reverential attitude towards sciencefound in many intellectual circles. Opponents of scientism argue that scienceis not the only valid form of intellectual endeavour,and not the uniquely privileged route to 121

r ? :'=F-knowledge.They often stressthat they are not anti-sr:it',',"r.. ig; . 7,,,,1 what they are opposedto is the privilegedstatusaccoxlt:rlt,r i science,particularly natural science,in modern society,rrrr

Despite the apparent impossibility of answering philosophical questions through science,quite a few contemporary philosophers do believethat scienceis the only legitimate path to knowledge. Questionsthat cannot be resolvedby scientific means are not genuine questions at all, they hold. This view is often associated with the late Willard van Orman Quine, arguably the rnost importantAmericanphilosopher of the 2oth century.The grounds for the view lie in a doctrine called'naturalism',which stressesthat we human beings are part and parcel of the natural world, r-rot somethingapart from it, as was oncebelieved.Sincescienr:estudies 122

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the whole of the natural world, surely it should be capableof revcalingthe completetruth about the human condition,leaving nothing left for philosophy?Adherents of this view sometimesadd that scienceundeniably makesprogress,while philosophyseemsto discnssthe samequestionsfor centurieson end. On this conception,there is no such thing as distinctively philosophical knowledge, for all knowledge is scientific knowledge. In so far as there is a role for philosophyat all, it consistsin'clarifoing scicntific concepts'- clearing the brush so that scientists can get on with their work. Not surprisingly,many philosophersreject this subordination of their discipline to science;this is one of the main sourcesof oppositionto scientism.Th"y argue that philosophicalenqrriry revealstruths about a realm that sciencecannot touch. Philosophicalquestionsare incapableof being resolvedby scicntiflc means,but are none the worse for that: scienceis not the only peth to the truth. Proponentsof this view can allow that philosoltlry should aim to be con^sistentwith the sciences,in the senseof not , advancing claims that conflict with what scienceteachesus. Anrl they can allow that the sciencesdeserveto be treated with grent respect.What they reject is scientific imperialism - the idea that scienceis capableof answeringall the important questionsalxrut man and his place in nature.Advocatesof this position usually think of themselvesas naturalists too. They do not normally hold that we humans are somehow outside the natural order, and so exempt from the scopeof science.They allow that we are just

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another biological species,and that our bodies are ultimately composedof physical particles, like everything else in the universe. But they deny that this implies that scientific methods are appropriate for addressingevery question ofinterest. A similar issue arises regarding the relation between the natural sciencesand the social sciences.Just as philosophers sometimes complain of 'scienceworship'in their discipline,so socialscientists sometimescomplain of 'natural scienceworship'in theirs. There is r23

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no denyingthat the natural sciences- physics,chemistry,rriorogy, ctc. - are in a more advancedstatethan the socialsr:it:nt:t,s _ economics,sociology,anthropology,etc.A number o{'pcoplc have wonderedwhy this is so. It can hardly be becausenatrrralscientists are smarter than social scientists.one possible answer is that the m'ethodsof the natural sciencesare superior to those of tlre social sciences.If this is correct, then what the social sciencesneed to clo to catch up is to ape the methods of the natural sciences.A.d to some extent, this has actually happened.The increasing use of mathematics in the social sciencesmay be partly a result of this sttitude. Physicsmade a great leap forward when Galilco took thc stcp of applying mathematical languageto the description of rut,tion; so it is tempting to think that a comparable leap lirrwarcl might be achievablein the socialsciences,if a comparableu,ay'f 'mothematicizing'theirsubjectmatter can be found.

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Ilowever, some social scientists strongly resist the suggestionthat they should look up to the natural sciencesin this way,just as some philosophers strongly resist the idea that they should look up to scienceas a whole. They argue that the methods of natural science are not necessarilyappropriate for studying social phenomena.why should the very sametechniques that are useful in astro'.nry, for example,be equally useful for studying societies?Thrse whr h'r
whether they are capable of answering every important question, we olrviously need to know what exactly those methods are. But as we have seenin previous chapters, this is much less straightforward a quegtion than it seems.Certainly we know some of the main features of scientific enquiry: indqction, experimental testing, observation, theory construction, inference to the best explanation, and so on. But this list does not provide a precise definition of 'the scientific method'. Nor is it obvious that such a definition could.be provided. Sciencechangesgreatly over time, so the assumption that there is a fixed, unchanging'scientific method', used by all scientific disciplines at all times, is far from inevitable. But this assumption is implicit both in the claim that scienceis the one true path to knowledge andin the counter-claim that some questions cannot be answeredby scientific methods. This suggeststhat, to some extent at least, the debate about scientism may rest on a false presupposition.

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Science andreligion

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The tension between scienceand religion is old and well documented. Perhapsthe best-known example is Galileo's clash with the Catholic Church. In 16.33the Inquisition forced Galileo to publicly recant his Copernican views, and condemned him to spend the last years of his life under house arrest in Florence. The Church objected to the Copernican theory becauseit contravened the Holy Scriptures, of course. In recent times, the most prominent science/ religion clash has been the bitter dispute between Darwinists and creationists in the United States,which will be our focus here.

Ncither thc scicntismissuenor the parallel issueabout natural and socialscicnr:cis ca.syto resolve.In part, this is becauseit is far firm clcar whrt cxrctly thc'methods of science',or the 'nreth'clsof nttural scitrncc',nctunllyconr;rrise- a point that is often overlooked lly lloth sid.n in tlrtrclehnte.lf we want to know whether the rrrctlrodnol'rcicnce nre np;rli.nbleto everysubjectmatter, or

Theological opposition to Darwin's theory of evolution is nothing new. When Ihe Origin of Specieswas published in 18d9, it immediately attracted criticism from churchmen in England. The reason is obvious: Darwin's theory maintains that all current species,including humans, have descendedfrom common aneestorsover a long period of time. This theory clearly contradicts the Book of Genesis,which saysthat God created all living creatures

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s' over a period ofsix days.So the choice looks stark: either you believe Darwin or you believe the Bible, but not both. Nonctheless, many committed Darwinians have found ways to reconcile their Christian f&i,thwith their belief in evolution - including a number of eminent biologists. One way is simply not to think about the cla.sh too much. Another, more intellectually honest way is to argue tlrat the Book of Genesisshould notbe interpreted literally - it should be regarded as allegorical, or symbolic. For after all, Darwin's theory is guite compatible with the existenceof God, and with many other tenets of Christianity. It is only the literal truth of the biblical story of creation that Darwinism rules out. So a suitably attenuated version of Christianity can be rendered compatible with Darwinism. However, in the United States,particularly in the Southern states, many evangelicalProtestantshave been unwilling to bend their religious beliefs to fit scientific findings. They insist that the biblical o account of creation is literally true, and that Darwin's theory of & c o evolution is therefore completely wrong. This opinion is knou'n as o 'creationism', and is acceptedby some .tO% of the adult population = ,c c in the US, a far greater proportion than in Britain and Europe. Creationism is a powerful political force, and has had considerable influence on the teaching of biolory in American schools,much to the dismayof scientists.In the famous'monkeytrial'of the tg2os, a Tennesseeschool teacher was convicted of teaching evolution to lris pupils, in violation of state law. (The law was finally overturned by the SupremeCourt in 1967.)In part becauseof the monkey trial, the subject of evolution was omitted altogether from the biology curriculum in US high schoolsfor many decades.Generations of American adults grew up knowing nothing of Darwin. o g o

This situation began to changein the 196Os,sparking a fresh round of battles between creationists and Darwinists, and glving rise to the movement called'creation science'.Creationists want highschool students to learn the biblical story of creation, exactly a^sit appearsin the Book of Genesis.But the American constitution 126

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prohibits the teaching of religion in public schools.The concept of creation scienbewas designed to circumvent this. Its inventors argued that the biblical account of creation provides a bett€r scientific explanation of life on earth than Darwin's theory of evolution. So teaching biblical creation does not violate the constitutional ban, for it counts as science,not religion! Across the Deep South, demands were made for creation scienceto be taught in biology classes,and they were very often heeded.In l98l the state of Arkansas passeda law calling for biolory teachersto gtve'equal time'to evolution and to creation science,and other statesfollowed suit. Though the Arkansas law was ruled unconstitutional by a federal judge in 1982, the call for'equal time'continues to be heard today. It is often presented as a fair compromise - faced with two conflicting sets of beliefs, what could be fairer than giving equal time to each?Opinion polls show that an overwhelming majority of American adults agree: they want creation scienceto be taught alongside evolution in the public schools.

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However, virtually all professional biologists regard creation science as a sham - a dishonest and misguided attempt to promote religious beliefs under the guise of science,with extremely harmful educational consequences.To counter this opposition, creation scientists have put great efiort into trying to undermine Darwinism. They argue that the evidencefor Darwinism is very inconclusive, so Darwinism is not establishedfact but rather just a theory. In addition, they have focused on various internal disputes among Darwinians, and picked on a few incautious remarks by individual biologists, in an attempt to show that disagreeing with the theory of evolution is scientifically respectable. They conclude that since Darwinism is 'just a theory', students should be exposedto alternative theories too - such as the creationist one that God made the world in six days. ln a way, the creationists are perfectly correct that Darwinism is . Just a theor/ and not proven fact. As we saw in Chapter 2, it is never possible to prove that a scientific theory is true, in the strict 127

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senseofproo{, for the inference from data to theory is invariably non-deductive. But this is a generalpoint - it has nothing to tlo with the theory of evolution per se.By the sametoken, we could argue that it is 'just a theory'that the earth goesround the sun, or that water is made of HrO, or that unsupported objects tend to fall, so students should be presentedwith alternatives to each of these. But creation scientists do not argue this. They are not sceptical about scienceas a whole, but about the theory of evolution in particular. So if their position is to be defensible,it cannot simply turn on the point that our data doesnt guaranteethe truth of Darwin's theory Iior the same is true of every scientific theory and indeed of most common-sensebeliefs too. lb be fair to the creation scientists,they do offer arguments that are specificto the theory of evolution. One of their favourite arguments cl is that the fossil record is extremely patchy, particularly when it E JI comesto the supposedancestorsof Homo sapieru.There is some o truth in this charge.Evolutionists have long puzzled over the gaps E o in the fossil record. One persistent puzzle is why there are so few o o 'transition fossils'- fossils of creaturesintermediate between two f species.If later speciesevolvedfrom earlier ones as Darwin's theory asserts,surely we would expecttransition fossils to be very common? Creationiststake puzzlesof this sort to show that Darwin's theory is just wrong. But the creationist arguments are uncompelling, notwithstanding the real difficulties in understanding the fossil record. For fossils are not the only or even the main sourceof evidencefor the theory of evolution, as creationists would know if they had read The Origin of STtecies. Compalative anatomy is another important source of eviclence,as are embryology,biogeography,and genetics.Consider,for example, the fact that humans and chimpanzeesshare 98% of their DNA. This and thousands of similar facts make perfect senscif the theory ofevolution is true, and thus constitute excellent evidencefor the theory. Of course,creation scientists can explain such facts too. 1'heycan claim that God decidedto makehumans and chimpanzees gcncticallysimilar, for reasonsof I lis own. But the possibilityof l

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giving,explanations'of this sort really just points to the fact that Darwin's theory is not logically entailed by the data. As we have seen,the same is true of every scientific theory. The creationists have merely highlighted the general methodological point that data can always be explained in a multitude of ways. This point is true' but shows nothing special about Darwinism' Though the arguments of the creation scientists are uniformly unsound, the creationist/Darwinist controversy does raise important questions concerning scienceeducation' How should the clash between scienceand faith be dealt with in a secular education system?who should determine the content of highschool scienceclasses?Should tax payershave a say in what gets taught in the schools they pay for? Should parents who don't want their children to be taught about evolution, or some other scientific matter, be ovemrled by the state? Public policy matters such as these normally receivelittle discussion,but the clash between Darwinists and creationists has brought them to

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ls sciencevaluefree? that scientific knowledge has Almost everybodywould unethical ends - in the manufacture of sometimesbeen used weapons,for examPle-But cases nuclear,biological, and that there is something ethicallY such as these do not objectionable about scien ific knowledge itself. It is the nse to which that knowledge is Put that unethical. Indeed, many philosophers to talk about scienceor scientific would saythat it makes no ical per se. For science is knowledge being ethical or have no ethical concernedwith facts, and facts in significance."It is what we do with moral or immoral. According to this vieq

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atr obvious Darwinian explanationfor why mice usually run away when they seecats. tn the past, mice that did not behavethis way tenrled to leave fewer offspring than ones that did, for they got eaten; assuming that the behaviour was genetically based,and thus transmitted from parents to offspring, over a number of generations it woul
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of theory will thus never be u determined by his data. Somc philosopherstal<ethis to that values are inevitablv involved in theory choice,and thus that sciencecannot possibly be value-free.A third argument is that scientific knowledge cannot be divorced fronr its intended applications in the way that value-neutrality rvorrld require. On this view, it is naive to picture scientists as disinterestedly doing researchfor its own sake,without a thought for its practical applications. l'he fact that much scientilic rcrscalch today is funded by private enterprises,who obviously h:rvcveste
Human sociobiologists(henceforth simply'sociobiologists') believe that many behavioural traits in humans can be given adaptationist explanations. one of their favourite examples is incest-avoidance. Incest - or sexual relations between members of the same family is regarded as taboo in virtually every human society,and subject to legal an
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in human societiestodaY. Though interesting, these arguments are all somewhat abstract they seekto show that sciencecould not be value free as a rnatter of principle, rather than identifying actual casesof values irrtnrcling in science.But specific accusationsofvalue-ladennesshave also been made. One such caseconcernsthe discipline called htrman sociobiology,which generated considerablecontroversy in thc 197Osand 198Os.Human sociobiologyis the attempt to appl.y principles of Darwinian theory to human behaviour. At firsl bluslr this project soundisperfectly reasonable.For humans are jrrst another speciesof animal, and biologists agreethat f)anvinizrn theory can explain a lot of animal behaviour.For exarnple,therc is 130

unclerstandably enough, many people feel uneasywith this sort of explanation. For, in efiect, sociobiologistsare saylng that we are genetically pre-programmed to avoid incest. This conflicts with tho common-senseview that we avoid incest becausewe have been taught that it is wrong, i.e. that our behaviour has a cultural rather than a bioiogical explanation. And incest-avoidanceis actually one of the least controversial examples.Other behaviours for which sociobiologistsoffer adaptationist explanations include rape, aggression,xenophobi4 and male promiscuity' In each case,their argument is the same: individuals who engagedin the behaviour 131

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out-reproducedindividuals who didn't, and the behavi'.r r'as genetically based,hence transmitted from parents to thcir offspring.Of course,not all humans are aggressive, xt:n'ph.bic, engagein rape. But this doesnot show that the sociobiol.gists 'r are wrong. For their argument only requiresthat thesebehavirrr's ha'. a geneticcomponent,i.e. that there is somegeneor geneswlrich increasesthe probability that its carriers u,ill engagein thc bchaviours.This is much weaker than saylng that the bchaviours are totally geneticallydetermined,which is armostcertainll,ialse. In other words, the sociobiologicalstory is meant to exprai' rvrrythere is a dEPositionamong humans to be aggressive, xenophdrir:,a'd t.
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Sociobiolory attracted strong criticism from a wide range of. Bcltolars.some of this was strictly scientific.critics poi'tcd ,ut that sociobiologicalhypotheses\ilere extremely hard to test, and shoulcl thun be viewcd as interestingconjectures,not establishecltr.'ths_ lfut othcrs objectedmore fundamentally,claiming that the rvhole rrrci'biologicalresearchprogrammewas ideologicallysuspect.T'rrey xttwit us an attempt to justifr or excuseanti-socialbehaviour, tusunllyby men. By arguing that rape,for example,has a gcnctic coutlrorrcnt,sociobiologistswere implying that it wa^s,natrrrzrl'and tlrus l.hutrapistswere not really responsiblefor their actions they wcrc sinrllly obcyingtheir geneticimpulses.'How ca. rve blar'e rupisLs,il'lhcir genesare responsiblefor their behavi'ur?,, tlrc n,cirlliologists seemedto be saying.sociobiologicalexplanations of xcnophobit and male promiscuitywere regardedas equally ;x:rrriciuus.'l'hey sccmedto imply that phenomenasuch as r.cisnr nnd rnuritrl i'lidclity, which most peopleregard as\rndcsir.ble, wtrrcn{rturalrurclincvitublc- tlrc product our geneticheritage. $f In slr,rt, crilics clr*rg.d thnt soci'biol'gy was a value-laclens<:ic'ce, turrl tlrc vriluesit wus ludcn witlr wcrc very dubious.perh.ps ttrrsrrr;lrinirrgly, tlrtrsccrit,it:sinclutlcdmany feministsand s,cial sr:icrrLisLr.

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One possible responseto this charge is to insist on the distinction between facts and values.Thke the caseof rape. Presumably,either there is a gene which disposesmen to rape and which spread by natural selection, or there is not. It is a question of pure scientific fact, though not an easyone to.ans'wer.But facts are one thing, values another. Even if there is such a gene,that does not make rape excusableor acceptable.Nor does it make rapists any the less responsiblefor their actions, for nobody thinks such a gene would literallyforce men to rape. At most, the gene might predisposemen to rape, but innate predispositions can be overcomeby cultural training, and everybody is taught that rape is wrong. The same applies to xenophobia, aggression,and promiscuity. Even if sociobiological explanations ofthese behaviours are correct, this has no implications for how we should run society,or for any other political or ethical matters. Ethics cannot be deduced from science. So there is nothing ideologically suspectabout sociobiolory. Like all sciences,it is simply tryrng to tell us the facts about the world. Sometimes the facts are disturbing, but we must learn to live with them.

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If this responseis correct, it means we should sharply distinguish the'scientifi c' objections to sociobiologyfrom the'ideological' objections. Reasonablethough this sounds,there is one point it doesn't address: advocatesofsociobiolory have tended to be politically right-wing, while its critics have tended to come from the political left. There are many exceptionsto this generalization, especiallyto the first half of it, but few would deny the trend altogether. If sociobiology is simply an impartial enquiry into the facts, what explains the trend? Why should there be any correlation at all between political opinions and attitudes towards sociobiology?This is a tricky question to answer.For though some sociobiologistsmay have had hidden political agendas,and though some of sociobiolory's critics have had opposing agendasof their own, the eorrelation extends even to those who debate the issue in apparently scientific terms. This suggests,though does not prove' that the'ideological'and'scientific'issuesmay not be quite so easy 133

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to separateafter all. so the questioir of whether sociobiology is a value-free scienceis less easyto answer than might have bc.rr supposed. To conclude, it is inevitable that an enterprise such as science, which occupiesso pivotal a role in modern society and conrmands so much public money, should find itself subject to criticism from a variety ofsources. It is also a good thing, for uncritical acceptanceof everything that scientists say and do would be both unhealthy and dogmatic. It is safeto predict that sciencein the 2lst century, through its technological applications, will impact on everydaylife to an even greater extent than it has already.so the question'is sciencea good thing?'will becomeyet more pressing. philosophical reflection may not produce a final, unequivocal answer to this question, but it can help to isolate the key issuesand encouragea rational, balanced discussionof them.

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Furtherreading

Chapter 1 ' A. Rupert Hall, Thn Reoolu?i.on in Scienn ISOO-1750(Iongman, 1983) containsa good.accountof the scientificrevolution. Detailedtreatment of particular topics in the history of sciencecan be found in R C. Olby, G. N. Cantor,J. R. R Christie,and M. J. S. Hodge (eds.),Conpaninn to the History of Modnn Scinue (Routledge, r99O). There are many good introductionsto philosophyofscience.Tfvo recentonesinclude AlexanderRosenberg,ThePhilasophyof Scimce(Routledge,zooo) and Barry Gower,Sci.entific MetDod(Routledge,1997).Martin Curd and (eds.), J. A. Cover Philosophy of Science:Tlu Central Issucs(W.W. Norton, 1998)containsreadingson all the main issuesin philosophyof science,with extensivecommentariesby the editors. Karl Popper's ca.nbe found in hlr attempt to denrarcatesciencefrom pseudo-science (Routledge, 1963).A good discussionof Conjechtresand,Rqfutationr Poppey'sdemarcation criterion is Donald Gillies, Philocophg of Sctctw in the 2oth Century (Blackwell,Part M 1993).Anthony OTIeu, Korl Popper(Rottledge, 198O)is a general introduction to Popper's philosophicalviews. Chapter 2 WesleySalmon, Tlu Foundation-sof Scinttific Infererwe(University of PittsburghPress,1967)containsa very clear discussionofdl the issuet raisedin this chapter.Hume'soriginal argumentcan be found in Book IV, section 4,of his Enquiry ConcerningHu:man Understanding, ed.

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