Reasons and Falsification Fred I. Dretske The Philosophical Quarterly, Vol. 15, No. 58. (Jan., 1965), pp. 20-34. Stable URL: http://links.jstor.org/sici?sici=0031-8094%28196501%2915%3A58%3C20%3ARAF%3E2.0.CO%3B2-Y The Philosophical Quarterly is currently published by The Philosophical Quarterly.
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REASONS AND FALSIFICATION More often than not a reason, or the giving of reasons, supplies a recipe, as it were, for the possible falsification of the statement or statements for which the reason is given. By this I mean that although some statements, considered in isolation, may appear irrefutable, they lose this invulnerability when taken in the context provided by evidential support. This is particularly true of existential statements, and, even more specifically, of those existentials which are not accessible to complete verification. Such, a t least, is the limited thesis which I would like to urge in this paper : any existential statement which cannot be conclusively verified through a direct encounter with that which is said to exist is, if there are any reasons for thinking it true, falsifiable. P u t in another way my claim is that there are no existential statements which combine all three of the following features : (1) there is some reason for thinking them true ; (2) they are unverifiable ; and (3) they are unfalsifiable. We have no reason to think any existential statement true which is both unverifiable and unfa1sifiable.l As the title indicates, I am primarily interested in exploring the relationship between the first and third features, reasons and falsifiability. Therefore, the inquiry will centre on existential statements which are not conclusively verifiable ; i.e., statements whose falsity is compatible with any k i t e number of observation statements. Since no observation will ensure the truth of these existentia,ls, they will be understood as being about some unobservable entity or process-something the existence of which cannot be conclusively ascertained by sight, touch, or other such direct confrontation. Certain existential hypotheses in science illustrate most vividly the type of statement now in question, but such existentials are not confined to science. Talk of one's " soul ", an " unconscious death-wish ", " spirits " and, in general, any sort of hypothetical cause, introduced for the explanation of certain events, can be subsumed under the present heading. When the existential is of this type, then, I submit, the giving of reasons in its favour exposes it to falsification. As I am using the term, a statement need not be false t o be falsifiable. A falsifiable statement is one for which it is possible to formulate a finite number of ob~erva~tion statements, statements describing what it is that one sees, hears, touches, etc., with which it is incompatible ; that is, a falsifiable statement is one that puts some limitation on the domain of possible 11 am ignoring those existentials which appear within systems of logic or mathematics (e.g., there is a prime number greater than two billion) ; my concern is with those statements which purport to say something, either directly or indirectly, about the spatio-temporal contents of our world.
REASONS A N D FALSIFICATION
21
observation statementse2 For example, the statement ' There is a t least one person now residing in Washington, D.C.', though not false, is falsifiable ; it is incompatible with a finite set of observation statements (representing an exhaustive search of the city) none of which contains the description of a persone3 I t is by now a familiar and accepted fact that there are unfalsifiable statements of this type. I n particular, the so-called " unrestricted " (" uncircumscribed " or " pure ") existential, embodying no spatial or temporal limitation on the location of that which is said to exist, supplies a virtually endless source of unfalsifiable statements : ' There are white ravens ', ' There exists a metal which does not expand if heated ', and so on.4 We cannot falsify these because we'icannot, in a finite number of observation statements, describe an exhaustive inspection of the universe. The following section, preparatory in nature, contains a discussion of reasons and their connection with that for which they are given as reasons. The results of Section I will then be exploited in the remainder of the paper in an attempt to demonstrate the close tie between reasons and falsi6cation.
I Let P be some proposition ; let Q be a reason for believing that P is truee5 Permitting ourselves only this much information, what can be said about the nature of P, Q, and the connection between thcm ? First, P and Q must possess truth values and their truth values must be related in some way. P and Q may be singular statements, general statements, or conjunctions of these ; they may even represent entire theories when we are adducing evidence in support of a theory or appealing to a theory as a reason for believing something else. Whatever the constitution of P and Q individually, though, they must not be totally independent in truth value. Q must a t least be relevant to the truth of P, and the matter of relevancy, when there is a question of giving reasons or adducing evidence, is a matter of related truth values. I shall say more about this relationship between P 2 1 am following the characterization given by J. W. N. Watkins in his " Confirmable
and Influential Metaphysics ", Mind, July 1958. Also see Karl Popper, The Logic of Scienti$c Discovery (New York, 1959), p. 86. aTechnically, of course, one would need the additional premise that this finite set of observation sentences represented an exhaustive inspection of the city's finite area. I assume, however, that this is given by the fact that the boundaries of the region are known and the search is designed systematically to cover the enclosed region. &Althoughunfalsifiable, these examples are verifiable. The first is taken from Popper, op. cit., p. 69 ; the second from Watkins, op, cit., p. 345. One must exercise some caution in constructing these examples, especially in relation to existential assertions about future events. For if the event is ascribed to the history of an object or person (or objects or persons) which has, or could have, a finite lifetime, then the failure of the event to occur before the object or person expired would provide a falsification, and the possibility of this would make the corresponding existential falsifiable. I t would, therefore, be safer to multiply quantify ; that is, one could ascribe the event to some (unspeoified) person or object a t some (unspecified) time in the future. 61t should be noted that this formulation automatically precludes some irrelevant (for our purposes) uses of the term ' reason ' ; Q cannot be the sort of reason one gives for doing certain things. For example : ' What was your reason for leaving early ? ' ' I had a n appointment.' I n this context the latter is not a value for Q since it was not offered as a reason for believing anything true.
22
TRED I. DRETSKE
and Q in a moment ; right now I should like to call at,tention to one other feature of P and Q individually. If Q is a reason for believing P true, then although P need not be true, Q must be. We can, and often do, give reasons-sometimes very good reasons -for believing something which is not true. My reasons for thinking I have ten dollars in my pocket may be very good ; I may even remember putting the money there this morning. Nevertheless, this is quite consistent with there not being ten dollars in my pocket. Therefore, except in the case where Q represents conclusive evidence for the truth of P, a case which we have already implicitly excluded by confining ourselves to unverifiable existentials, P may be either true or false. Of course, the presence of Q makes it more likely that P is true, but this again is compatible with P not being true. On the other hand, Q must be true. If Q is false, it is not a reason for believing P, although its relation to P might be such that it would be a reason for believing P if it were true. One may think that Q is true and, as long as this conviction persists, one may also take it as a reason for thinking P true. But any challenge to the truth of Q is simultaneously a challenge to the acceptability of Q as a reason. To put it another way, Q must be taken as true in order to be taken as a reason. The simple utterance, ' His temperature is 102" ' is not, qua utterance, a reason for thinking Jimmy has a fever ; it is only in so far as such an announcement carries with it the presumption of truth (and this is generally a matter of context) that it will function as a reason. Returning to the question of the relationship between P and Q, it should be clear that whenever Q is adduced as a reason for believing P, there is always an implicit or explicit appeal to (reliance on) considerations of a general nature, some regularities or uniformities, by virtue of which the likelihood of P's being true is increased by the truth of Q. The appeal to such general truths is explicit when their expression is found within P or Q themselves ; more often it is implicit. For example, when one advances as one's reason for believing that a certain house will soon be occupied (P) the fact that the real estate agent has just removed the " For Sale " sign (Q), one is relying on ,the truth of some generalization of the sort : Real estate agents (or, perhaps, this real estate agent) normally remove such a sign only after having closed a salee6 This appeal is often left implicit on the presumption that the listener is familiar with the regularity which makes the real estate agent's behaviour (removal of the sign) a reason for thinking that the house will soon be occupied. Nonetheless, it is such generalizations, however t ~ i v i aand l half recognized they may be, which establish the connection between P and Q. When these generalizations are implicit, one can " spot " them by asking which statement or statements are such that if they were false, Q would no longer be a reason for thinking P true. I n our example one could identify the remaining implicit generalization (see foot@Strictlyspeaking we should also mention the assumption that people generally occupy a house shortly after purchasing it.
REASONS AND FALSIFICATION
23
note 6) by asking whether the real estate agent's removal of the sign would still be a reason to think that the house was about to be occupied if it were false that most people who purchase a house occupy it shortly thereafter. I should like, for purposes of abbreviation, to refer to these generalizations, these truth-value links between P and Q, as relevancy-making generalixations. The truth of such generalizations makes the truth of Q relevant to the truth of P ; when the relation is such that the truth of Q increases the likelihood of P's being true, then Q (if true) is a reason for P. The term 'relevancy-making generalization' is intended to highlight a certain function which general statements sometimes have : viz., their service in relating reasons to that for which the reasons are given7 Before leaving this discussion one further point should be made about relevancy-making generalizations as they pertain to existential statements. When P is an existential, a given relevancy-making generalization may either (1)express part of the defining characteristics of that which is said to exist, or (2) be a contingent truth about the hypothetical entity. I n the former instance one commits oneself to the truth of the generalization in the process of asserting the existential ; e.g., in asserting that there are human beings on Mars one is committed (unless explicit qualifications are made) to recognizing creatures having those traits defining humans-visibility, intelligence, spatio-temporal continuity of body, etc.. Some of these traits may be unpacked as generali~at~ions about human beings ; a Martian, being human, and thus visible, is such that if, under specifiable conditions, one looks a t a Martian, one mill see him. To such trivial, but nonetheless significant, generalizations as this, embodied within the very notion of that which is said to exist, one commits oneself in maintaining the corresponding existential. I n the second case one also accepts the truth of certain relevancymaking generalizations, not in asserting the existential itself, but in the act of giving reasons in itjs fa,vour ; for, as we have seen, the adduction of a reason relies on the truth of some relevancy-making generalization. Deny the truth of this generalization and one simultaneously denies that a reason has been given. The relevancy-making generalization is not, in this case, ZogicalZy related to either P or Q ; ' Real estate agents normally remove " For Sale " signs only after having closed a sale ' does not entail, nor is it entailed by, either P (' This house will soon be occupied ') or Q (' The real estate agent just removed the " For Sale " sign '). Yet, anyone giving reasons in the manner described must concede its truth. I n either case, then, the giving of reasons for the truth of an existential carries with it, either in the existential itself or in the assumptions upon which one's reasons rely, the assurance that, for the moment a t least, certain general truths are being granted. 7 1 have not discussed the scope of these generalizations ; i.e., how general they must be in order to function as relevancy-making generalizations. This subject will be taken up in the latter portions of section 111,
REASONS A N D FALSIFICATION
25
these relevancy-making generalizations, " fixes " some definite features and, simultaneously, by virtue of these same generalizations, relates these features to some observable phenomena. The generality of these connecting links establishes a multiple connection with observable states of affairs, not a singular one with that specific state of affairs appealed to in one's reason ; these give rise to expectations regarding other observable phenomena-expectations which, by being disappointed, may lead to the existential's falsification. If, however, the nature of these connecting generalizations is such that no expectations are generated, then the existential will be found to have such a diminished content that it will be conclusively verifiable. Let me develop this argument by adapting Wisdom's example of the invisible gardener.8 Since this example illustrates all the essential features of the connection between reasons and falsification, I will, in the following section, discuss it a t some length.
Two men differ on the question of whether a gardener has been active in their garden while they were absent. The one, call him Peter, contends that a gardener has been present, because of certain striking signs (call them, collectively, P) of the neglected (by its owners) garden ; e.g., surprisingly vigorous growth of the plants, orderly arrangement of the flowers, etc. The other, Thomas, disagrees on the grounds that no one has observed a gardener to arrive, work, or depart, the weeds are still plentiful, and there are no other traces of a human being, such as footprints, tools, etc. I n the face of this counter-evidence Peter modifies his hypothesis to the claim that an invisible gardener was present during their absence ; moreover, this gardener did not possess any of those normal properties (normal in relation to gardeners) which would have produced the sort of traces that were expected but not found. Disagreement persists. The important aspect of this dispute is that rather than accept the absence of certain anticipated traces (anticipated on the basis of what is commonly known about gardeners and their activities) as reasons against the existence of a gardener, Peter neutralizes these considerations by appropriately modifying the nature of that which is said to exist. He does not contend that the relevancy-making generalizations on which Thomas relied in giving his counter-evidence (e.g., anyone with appreciable weight who steps in soft dirt will leave a footprint) are not uniformly applicable to gardeners ; for he has no foundation for this claim except by arguing in a circle, vi5., that the present case, on the assumption that a gardener was present, shows that the generalization is not uniformly applicable. Instead, Peter argues that the " gardener " (the quotes signifying that the term is now being stretched beyond its normal application) does not have those properties (e.g., weight) ordinarily associated with 8" Gods ", reprinted in Philosophy and Psychoanalysis (Oxford, 1957), pp. 154ff.
26
FRED I. DRETSEE
gardeners and, hence, the relevancy-making generalization is inapplicable in this case. In other words, the absence of footprints is irrelevant to whether Peter's " gardener " was present or not. By modifying the content of the existential (the properties B, C, D, . . . referred to above) Peter eliminates the reasons against the hypothesis but retains the reasons in its favour (i.e., the relevance of F). Ad hoc as this may be, the fact remains that the hypothesis, in its altered form, may be said to have a t least one reason in its favour but apparently no reasons for thinking it false (aside from considerations of simplicity or economy of hypothesis) ; a t any rate, there is no obvious way to falsify it as I have defined falsification. Artificial as this example is, it illustrates the pattern of an existential statement for which there is some evidential backing but which is, prima facie, unfalsifiable. Recalling our previous discussion, one can drive an entering wedge into Peter's position by noting that whenever a reason is given for thinking some entity exists, a t least one relevancy-making generalization is being taken as true. I n the present instance, the invisible gardener, although non-human (being stripped of most of those traits generally characteristic of humans), does possess a t least one positive property-an abiding interest in gardens and, during the absence of their owners, their care and maintenance. This, however, is the only link between Peter's unobservable gardener and observable states of affairs that has been conceded ; Peter cannot abandon this link on pain of losing the only reason he has for thinking the gardener exists. Capitalizing on this fact, one can point out that the presence of one generalization of this type is sufficient to make the existential falsifiable. The gardener, as this term is now to be understood, is " the agency " (or some equally generic term) " which cares for neglected gardens " and it would seem, lacking any qualifications on this characteristic (we shall consider several qualifications in a moment), that one is warranted in expecting this behaviour to be manifested on repeated occasions when any garden (or, perhaps, this garden) is left in a state of neglect. If there is a gardener, and if he cares for gardens neglected by their owners, then we have a falsifiable hypothesis ; it is incompatible with the set of observation statements describing the disorderly state (i.e., lack of condition F) of a garden (or this garden) neglected by its owners. Attention should be called to the fact that this is a falsification of the existential which asserts that the gardener exists. For what is said to exist is an agency which, among other (unspecified) things, cares for neglected gardens, and if neglected gardens, any of them, are not cared for, then this agency does not exist. We may set this out in some detail as follows : let ' Ax ' stand for ' x is a gardener ' (in Peter's modified sense) ; ' Cxy ' for ' x cares for y ' ; ' Gx ' for ' x is a garden ' ; ' Nx ' for ' x is neglected by its owners ' ; and ' F x ' for the condition of the garden to which Peter appeals in his reason (vigorous plants, arrangement of flowers, etc.). As the term ' A ' is now being used by Peter, the only positive content assigned to this
REASONS AND FALSIFICATION
27
gardener is the property of caring for neglected gardens ; hence, we can treat the term ' -4 ' as partially defined as : (l) Ax = df (Y) [(GY.NY)>Cxyl . i.e., for x to be a gardener in this sense is, a t least, to be such that if there is a neglected garden, then x cares for it. Furthermore, one must assume, as an additional relevancy-making generalization, that if any garden is cared for by someone, then it will, among other things, be brought into condition F. (2) (4 (y) E(Gx.Cyx) 3 Fxl This assumption is necessary to make the observation about the well-kept state of the garden (F) a reason for thinking that someone cared for it.9 If, contrary to this assumption, gardens were not generally brought into condition F by someone's care, then the condition of the garden would not be a reason for thinking that anyone, much less the invisible gardener, cared for it. By virtue of (1) Peter's existential, (Ex)Ax, can be written (or, if (1)is taken as only a partial definition, Peter's existential statement implies) : (3) (Ex) (y) [(GY.NY)2 Cxyl which, together with the relevancy-making generalization (2), implies that Peter's garden will, in his absence, be cared for and brought into condition I?. The hypothesis, in a sense, accounts for the observed state of the garden and this is the ground for our saying that Q (a description of this state of affairs) functions as a reason for the existential. However, the discovery of a neglected garden which is not in condition F gives us the observation sentence, (4) Ga.Na .-Fa which implies (via (2))the negation of (3) and, hence, the negation of Peter's existential. Strictly speaking, this is not a falsification as I have previously defined it, since the observation sentences do not, by themselves, imply the falsity of the existential ; rather, (2) is used in deriving the negation of the existential. The point is, however, that this assumption (2) is necessary to have the condition F of Peter's garden function as a reason for the existential ; the falsification assumes nothing that is not already assumed in the act of giving reasons. Therefore, if we have a reason for thinking the existential true (in its present version), then it can be falsified. I t might be supposed that if our alleged gardener was taken to care, not for all neglected gardens (or not for this garden every time it was neglected), but for a certain percentage of neglected gardens or for most neglected gardens (the question of some neglected gardens will be taken up shortly), the existential asserting his existence could not be falsified so easily. I n one sense this is certainly true, since the falsification would encounter those difficulties associated with the falsification of probabilistic statements about infinite, or a t least indehitely large, collections (we could consider our
.
@Thisimplication could be reversed or the entire statement made into a bi-conditional, but this would only make the defence of my thesis that much easier. Reversing the implication would have the effect of making one's reason, Q, a conclusive reason for 1' and, hence, 1' would be completely verifiable.
28
FRED I. DRETSKE
collection of neglected gardens indefinitely large by counting all past, present, and future gardens). Since one's sample is never as large as the collection of which it is the sample, one cannot deductively infer (and it is this type of inference which would be required for strict falsification) that the whole does (or does not) exhibit the proportion found in the sample. In particular, we could not infer that because only one out of five hundred examined gardens were cared for in the absence of their owners, that most neglected gardens were not cared for. Therefore, no h i t e set of observation statements would imply that there is no gardener who cares for most neglected gardens. I t seems questionable to suppose that we still have a reason for believing in this altered version of the existential hypothesis. If the fact that Peter's garden was in condition F is a reason for believing in the existence of a gardener, it would seem that it is a reason for believing in one that cares for all (or, perhaps, some) neglected gardens, but not for one that cares for X per cent of neglected gardens where X is not equal to one hundred. We have one favourable case and no unfavourable cases ; if this indicates any ratio of neglected gardens that are cared for, it indicates one hundred per cent. Nevertheless, it may be replied that if we have a reason for believing in a gardener who cares for all neglected gardens, we have an equally good reason for believing in a gardener who cares for more than fifty per cent (i.e., most) neglected gardens ; hence, we do have a reason for this second form of the existential hypothesis and it, in contrast to the first version, is not falsifiable. It must be granted, I think, that the existential, as it now stands, is strictly unfalsifiable. Unless we assume that there is a finite number of neglected gardens, we cannot, in a finite number of observation statements, falsify the existential statement asserting that something exists which has the property of caring for most neglected gardens (i.e., puts them in condition F). Nevertheless, we can say this much. However large the sample appealed to in one's reasons (in our example the sample is only one neglected garden), the fact that the ratio in that sample is being accepted as indicative of the ratio in the entire collection, assures us that he who adduces the ratio in this sample as a reason must be willing to accept a larger sample with a significantly different ratio as counter evidence. The fact that Peter thinks the condition of one neglected garden a reason for thinking that most neglected gardens are in the same condition, commits him to granting that if only one out of four neglected gardens are in that condition, then, most likely, most neglected gardens are not cared for. To deny the weight of this latter evidence is to deny that his original reason had any weight. Hence, even if Peter will not accept the unfavourable ratio in the larger sample as a strict falsification of the existential hypothesis, he must, a t the very least, grant that it is a much stronger reason against than he originally had for the existential. Practically speaking, of course, we would treat an unfavourable ratio in a very large sample as a falsification of the hypothesis that most neglected gardens were cared for, and, in this sense, the hypothesis is falsi-
REASONS AND FALSIFICATION
29
fiable.1° Therefore, when giving reasons for existentials of the present type, the possibility always exists of falsifying it in the practical fashion just described or, what amounts to the same thing, showing that there are no reasons for thinking it true (due to the absorption of the original sample into the larger, unfavourable, sample) but strong (stronger than one's original) reasons for regarding i t false. There is a way, attractive a t first glance, in which the existential might be modified even more drastically in order to avoid even that degree of vulnerability just discussed. I t may be denied, for example, that this invisible gardener acts in the regular or predictable fashion heretofore envisaged. Being somewhat whimsical, he cares for neglected gardens only sometimes and in some places. Although we can expect no regular behaviour on the part of this capricious gardener, the fact that this (Peter's) garden has been cared for in the absence of its owner is some (admittedly slight) reason to think that he not only exists but has recently been active. Unlike the previous case, the examination of other neglected gardens will not undermine this reason, nor will it provide counter-evidence-much less a falsification. The logic of this situation has suddenly shifted. Thomas is now faced with a truly unfalsifiable hypothesis-some invisible agency cares for some gardens neglected by their owners. I t is even difficult to imagine how subsequent observations of any type could supply reasons against this hypothesis. However, the nature of the connection between Peter's reason and the existential for which he gives the reason has also radically changed. There is nothing in the present hypothesis which implies, as it did in the first case, that this garden would be cared for in the absence of its owners or, as in the second case, that the probability of this garden's being cared for was greater than one half. M h t , then, is the connection between Peter's reason and the existential he is endeavouring to support ? It would seem that the direction of the connecting implication has reversed itself. That is, if Peter has any reason for believing the existential true, if there is a connection between the truth values of P and Q which makes the truth of Q increase the likelihood of P's being true, then he has conclusive reasons since Q (his reason) now implies P (the existential). To see that this is so, one need only recall what it is that is being said to exist : viz., some agency which cares for some gardens in the absence of their owners. I n terms of the abbreviations already used we can write the existential as :I1 lOFor a full discussion of the falsification of probabilistic statements, involving the notion of a " rule of rejection ", see R. B. Braithwaite's Scientific Explanation (Cambridge, 1955), Chapter VI. Also compare the following remark by Popper : " Probability statements, in so far as they are not falsifiable, are metaphysical and without empirical significance ; and in so far as they are used as empirical statements they are used as falsifiable statements " (op. cit., p. 204). 1 1 8 special case of this sort of existential hypothesis is where the gardener is supposed to care, not for some (unspecified) garden, but for Peter's garden (and, perhaps, only Peter's garden). The following remarks will also apply, mutatis mutandis, to this special case. Notice that the existential, P, is being formulated in terms of the one positive
30
FRED I. DRETSKE
(PI (Ex) (EY)(GY.NY.C~Y)> i.e., there is something which cares for some gardens neglected by their owners. Peter's reason can be written (letting ' p ' designate Peter's garden) : (Q) Gp.Np.Fp, i.e., Peter's garden was found in condition F when neglected. What then, is the connection between P and Q which makes Q a reason for believing P true ? If we assume that if something cares for a neglected garden, then it will acquire condition F, (x) [(Gx.Nx.(Ey)Cyx)3 Fx], this will not serve as a relevancy-making generalization since it, in conjunction with P. is quite independent of Q-the fact that some gardens are brought into condition F by someone's care does not imply, nor does it, even make it more likely, that Peter's garden will acquire condition F. What we must assume, in order to relate the truth values of P and Q, is that nothing- else but someone's care can bring a garden into condition F ; i.e., that neglected gardens which are found in condition F have been cared for by something : (G) (x) [(Gx.Nx.Px) 3 (Ez)Czx] This assumption is necessary since to deny G is to admit that some neglected gardens can acquire condition F without being cared for by anything. Without this assumption the discovery of a garden in condition P is no reason, by itself, to think that anything cared for it,-not unless one has some other, independent, grounds for thinking that it did not come about by itself (i.e., without something caring for it). In other words, to deny G is to admit that finding a garden in condition F is no reason to think that something cared for it because some gardens (and we have no suggestion as to how many) are in condition P without anything caring for them. I t is only if one had some reason to think that Peter's garden was not one of those which acquired F by itself that one would really have a reason for thinking that someone cared for Peter's garden ; but, again, this supplementation of Q with this further information would constitute a new reason with new relevancy-making generalizations, and a similar analysis could be undertaken. As things stand, Q is a reason for P only by virtue of G ; but if G is granted, then Q is a conclusive reason for P (Q, together with G, implies P). Hence, in this limiting case, P is completely verifiable. The only assumption needed to make P completely verifiable is the one which is necessarily assumed in construing Q as a possible reason for P. This is property being ascribed to the gardener ; the fact that he is not human (i.e., not visible, weightless, etc.) is being omitted for the sake of simplicity. If such negative properties are explicitly ascribed to our hypothetical gardener, then the existential, P, would have to be written : (p') (Ex) [-Hx.(Ey) (Gy.Ny.Cxy)l where the ' H ' comprises those properties characteristic of humans. Formulating the hypothesis in this fashion, however, would not diminish its verifiability since the gardener's lack of the property H (if not already verified by Thomas's counter evidenceviz., no one saw a person arrive or depart, no footprints, etc.) is verifiable (by stationing suitable observers) on another occasion in respect to another neglected garden which acquires the condition F. If no human is observed to care for the garden and the garden acquires condition F, then this information (together with the argument now being given in the main text) constitutes a conclusive reason for believing that P' IS true.
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31
n hat I originally meant by saying that in the context provided by evidential support (i.e.. on the basis of the assumptions thereby required) a statement is either verifiable or falsifiable. One last point regarding this example : u e cannot c o n ~ t r u eG as probabilistic (implying n i t h probability greater than one half that someone cared for the garden) In order to avoid complete verifiability of P (by Q) . for to (lo this is to admit that a neglected garden in colldltioll F needs no explanation of the type being proposed. As poillted out in the last paragraph, the admission that some gardens call acquire condition F xithout anyone's care makes it completely gratuitous to suppose t h a t the discovery of a garden in condition F is a reason to suppose something cared for it. The olily way this conditional can be understood as probabilistic is if there is some n a y to distinguish betnecn a neglected garden in condition F for nhich someone cares and one for n hich no one cares. Lacking any specifiable clifference of this sort, the value ' p ' of the probability n ould be completely arbitrary : it could range anynhere from zero to one hundred nithout affecting a single observation. If there is no difference betneen a garden for uhich someoile cares and one for nhich no one cares, then the only choice n e have is to admit that the hypothesis that some of the gardens in condition F are cared for is superfluous (accounting for no more than nould be accounted for n lthout such a supposition) or to admit that somethillg cares for all of them ( nhich a t least pz~rportsto explain hou the condition F comes about). I n the first case n e have no reason and in the second case our reason is coaclusive. The detailed analyqis of this single example illustrates the logical connections betnee11 reasons and falsifiability. I t is a fairly simple matter to formulate unfalsifiable existentials , the clifficulty appears in trying to maintain this status nhile giving reasons for thinking them true. For these reasons, by ~rirtneof their relevancy-making generalizations, tie the hypothetical entity cr entities to observable states of affairs in some uniform n a y : once this connection is granted, the possibility a r i ~ e sof falsifying the existential by shoning that the expected regularities do not materialize. If, on the other hand, the relevancy-making generalizatiolls establish no regular connection n i t h observable states of affairs (such as that appealed to in one's reasons), the content of the existential is found to be so attenuated that the direction of the connecting implication reverses itself and one's reasons become conclu~ive.~" 12Cf. P;. R. Hanson . " TVheneler an explanatory' h~potheslshas as ~ t sconsequences o n l ~those anon~alousphenomena fol which we oliginall) sought an rxplanatlon, that hlpothesis n l a ~qnlte iightlg be regarded as being but a ' quasi-explanatorg ' r e ~ t u t e r i l e ~ toft the \ e l ) descriptions with which the enqun) began " ( The Law of Inertla . -4 >'hilosopher's Touchstone ", Phtlosophy o j S ~ l e l t c e , Apr:l 1963. p 115, note 12). I hale expressed much the same polnt of xiew bs algwng illat these ad hoe explanations are, In general, conclusir elg vellfied by the eridence orlgmall~adduced m thelr faroul ; in this sense they are a lestatement of that elidenee.
FRED I. DRETSKE
IV Many scientific hypotheses illustrate the features sketched in the last section although this is sometimes obscured by the fact that as soon as an existential hypothesis is falsified (and they frequently are falsified), a new hypothesis is introduced without a significant alteration in terminology.13 The retention of the old terminology (the names for the hypothetical entities) conveys the impression that the existential is independent of the more susceptible generalizations describing the behaviour of the hypothetical entities. It is the generalizations, or so it is thought, which are continually modified in the face of unfavourable results. But it should be clear that these generalizations (functioning as relevancy-making generalizations) actually determine the nature of that which is said to exist in the existential hypothesis ; alter these generalizations and you alter what it is that is said to exist-just as the neutralization of Thomas's counter-evidence by the alteration or elimination of certain relevancy-making generalizations was, in effect, a modification of what it was that Peter said existed.14 Let me cite just one example from the history of science to illustrate further the analysis in the last section. As an explanation for what we now take to be correctly explained by the force of atmospheric pressure, a funiculus, an invisible membrane or filament, was once postulated to account for the rise of a mercury column in a Torricellian tube. This funiculus was supposed to support the mercury by pulling upward on it with a force sufficient to maintain the column of mercury a t approximately twenty-nine inches.15 Since, in normal circumstances, the column could not be made to attain a level higher than twenty-nine inches, the funiculus (in order to explain this maximum point) was supposed to possess a corresponding maximum tensile strength. The analogy with a cord or thread with enough tensile strength to maintain the fluid a t such a height is obvious, but the analogy ends with this one property. The funiculus was neither visible nor tangible ; its sole function resided in its ability to support the mercury a t the standard (or less than standard) height. Odd as this hypothesis may seem, there was some reason to think it true ; it explained the observed phenomena in the sense that if this hypothesis were true, then one could expect mercury and other fluids to manifest the effects of this membrane's " pull ". But although the mercury's regular behaviour could be taken as evidence for the existential hypothesis, the use of it as evidence also exposed lSMario Bunge, faced with the acknowledged fact that existential hypotheses do occur in science, but also believing, erroneously, that they cannot be falsified, is led into such inconsistencies as : " If a piece of factual knowledge is not in principle refutable, then it does not belong to science but to some other field " (Metascienti$c Queries (Springfield, Illinois, 1959) p. 54) ; and " That indefinite existential hypotheses are irrefutable is obvious ; that they are nonempirical or extrascientific must be denied " (" Kinds and Criteria of Scientific Laws ", Philosophy of Science, July 1961, p. 272). 14Cf. Quine, Word and Object (New York, 1960), p. 16 : . our coming to understand what the objects are i s for the most part just our mastery of what the theory says about them. We do not learn first what to talk about and then what to say about it ". Isconant, Harvard Case Histories i n Experimental Science (Cambridge, Mass., 1957), pp. 50 ff.
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REASOKS ARD FALSIFICA4TION
33
the hypothesis to falsification. Robert Boyle's observation that mercury could rise to much greater heights in certain circumstances provided tliat falsificatlon.l"f the origiilal hypothesis n a s in terms of a i"urliculus u i t h a nzazirnum tensile strength (and this is the kind of ful~iculusfor nhich we had a reason), then Boyle's experiment falsifies that hypothesis by shoning thdt the supporting agency does not have that one property 1111icil originally dtfined it (haring such-and-such maximum tensile strength). If, on the other haad, TIC suppose that the original reasorl n a s simply in favour of sovze supporting agency, a n agency nhich r ~ ~ o u lsuppoit d the mercury a t r~41alererheight it might be found a t , then the expriiment clearly does not falsify such an hypothesis. but, as TIC have already argued, the reasons one ha, for it are conclusire. For u h a t is it for uhich one is giving reasons ? I t is t h t t some agency " (the cord or membraile analogy can only mislead at, tllis point since the furliculus has ?zone of the anrlogous piopertie.) supports the mercury at n hatever height it is found a t . That tilere is some agency rehponsible for the mercury's beha\-iour can haidly be dcnied except by del~yingthat the mercury bchares as it does. From thc fact ?hat the meicury columrl is a t some height (and these are the facts bcing adduced as reasons) one car1 infer that s o m e t h i ~ gis resporlsible for maintainiilg it a t this height. If orle takes this " responsibility " in some casual, quasi-mechanical sense, theil it nould be necessary (in order to deduce the Iiypothesis from the reason) to assume that there n a s some quasi-mec1,anical cause for every 5uch evei~t: but this assumptiorl is necessary in urly caqe since otherx~ise the. mercury's behaviour nould not be a reasoil for believiag in any hypothesis of the sort nhich the f ~ ~ n i c u l uhypothesi: s rtpresents. If this " responsibility " is understood i11 some rague and indeterminate u a y , oae's reasoils ale simply ail alternatire description of what is described in the existential hypothesis itself : for to deny that something is responsible i11 this sense is. ill effect, to deny that the phenomerla appealed to in oae's reasoil exist. "
V This analysis is sketchy and in marly respects incomplete. I have, for example, assumed that one's reasons are always a description of some obser\-ablc phenomeiia x i t h uhich the hypothetical entity or entities were presumably related by various relevancy-making generalizatioas. Ho11 erer, it may occur, as x i t h Dirac and the positroil, that the mathematical structure involved in a theory's articulation points t o the existence of certain particles whose existence has not yet beer1 suggested by any experimeiltal inrestigations. If the theory is adequate in other respects. this may afford some reasorl to beliere that such particles exist, but it does not immediately 1%03le demonstrated this by constructing a " J " tube n i t h the long leg open and the short leg sealed. By pouring mercury in the tube, the compressed air in the short leg (together with Boyla's " sucking with his ino~ith" at the open end of the long leg) inamtamed a coluinn of nlercury a t approximately elghty-elght inches above that colunln in the short leg. (Ibid., pp. 52 ff.)
34
FRED I. DRETSKE
suggest a way of falsifying an existential statement about such particles. I have also ignored the complications which might arise if the hypothetical entities were given a multiplicity of properties expressly designed to circumvent the sort of considerations already presented. I cannot hope to anticipate all the counter-examples which a n inventive detractor might formulate ; I have said all that I can usef~~lly say in a general way about the connection between reasons and falsifiability for existential statements about unobservable entities. Specific hypotheses designed to exploit whatever lacunae there might be in this analysis would demand iildividual treatment. Nevertheless, I do hope to have shown that the giving of reasons in favour of a n existential hypothesis tends to expose that hypothesis to methods of testing and, in marly cases, falsification of one form or another. Karl Popper has observed that ". . . an isolated existential statement is never falsifiable ; but if taken in a context with other statements, an existential statement m a y in some cases add to the empirical coilteilt of the whole context ; it may enrich the theory to which it belongs, and may add to its degree of falsifiability or testability ".I7 An appropriate way to uilderstand this " context " t o which Popper alludes is, I submit, as the context consistiilg of our reasons for thinking the existential statement true. I have tried to show that in this context the existential will always be falsifiable (or, perhaps, verifiable). There is no assurance that every " new idea, put up tentatively, and not yet justified i11 any way ",la can be tested, and hence, no assurance that falsifiability is a n effective criterion for demarcating scientific from non-scientific hypotheses. The point here is that prior to the testing and attempted falsificatiorls of " freely created " hypotheses there must come a stage where we filter out those hypotheses which we have some reason to think true ; there must be some justification, even if this be a crude and imprecise explanation of those events for which an hypothesis is desired. Unless this proviso be added there is no assurance that certain existential hypotheses, which to all appearances are scientific in nature, are even testable. It has been the purpose of this paper to argue that with this proviso, existential hypotheses will coilform more closely with Popper's criterion of demarcation between scientific and non-scientific hypotheses ; existential .hypotheses for which we have some (but cannot have conclusive) evidence will, or so I have argued, be falsifiable.
FREDI. DRETSKE University of Wisconsin. 1 7 0 ~ .cit., p. 70, note 1.
lslbid., p. 32.
