Lost Knowledge Fred Dretske; Palle Yourgrau The Journal of Philosophy, Vol. 80, No. 6. (Jun., 1983), pp. 356-367. Stable URL: http://links.jstor.org/sici?sici=0022-362X%28198306%2980%3A6%3C356%3ALK%3E2.0.CO%3B2-S The Journal of Philosophy is currently published by Journal of Philosophy, Inc..
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H E received view is that knowledge is a n enriched form of belief, a belief whose truth is somehow vouchsafed by a n appropriate relationship (causal? justificatory? nomic?) to the facts. According to this view of things a belief can change its cognitive or epistemic character without altering its status as a belief. It can begin its life as a cognitively impoverished, but otherwise healthy, belief and, by suitable enrichment, become a piece of knowledge. Or it may lose this relationship, suffer an epistemic relapse, while retaining its doxastic vigor. We are certainly familiar with this process occurring in one direction-a belief b e c o m i n g knowledge. I believe, in fact I'm absolutely certain, that my car is in t h i s row of the parking lot. I'm certain about this because I (think I) remember putting it here this morning. In this case, though, my certainty is the result of a confusion. I don't actually remember putting the car here this morning. What I actually remember are my activities yesterday morning (when I did park it here). So, though I believe it, I don't really know my car is in this row. Trudging down the lane I spot my car, exactly where I (thought I) remembered putting it this morning. Dumb luck. My belief that my car was in this lane has been promoted, in this case by perceptual evidence, into a piece of knowledge. Is this process ever reversed? We certainly lose knowledge but this, remember, is not the issue. T h e question is whether we can lose it m e r e l y by disenfranchising the belief. It is, after all, easy enough to rob someone of knowledge by changing his beliefs. In a perfectly sincere and honest mood I tell you about an indiscretion of mine. Later, regretting the potentially embarrassing revelation, I convince you I was lying-or, perhaps, that you misunderstood me. "I was just boasting," or "Didn't you realize I was talking about my friend Ralph?" Originally, of course, you knew something: that I did it. You no longer know this and the reason you T h i s paper developed o u t o f a disagreement between t h e authors a b o u t the c o n c l u s i o n s t o b e d r a w n f r o m a n e x a m p l e i n Dretske's "A C o g n i t i v e Cul-de-Sac," M i n d , xc I , 361 ( J a n u a r y 1982): 109-1 11. For t h e record, a n d this should be apparent b y c o m p a r i n g t h e earlier paper w i t h this o n e , Dretske lost this a r g u m e n t . T h e a u thors w i s h t o t h a n k Dennis S t a m p e and Berent Enc f o r u s e f u l c o m m e n t s o n earlier drafts. 0022-302X 83 8006 0356901 10
1983 T h e Journdl o f P h i l o s o p h y , Inc
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don't is that, thanks to my powers of persuasion, you no longer (even) believe it. But this, again, is not the issue. The question is: can we leave the person with his belief but rob him of the knowledge? One of Gilbert Harman's examples (slightly modified here) suggests that we can.' Everyone knows that the king is dead. They all watched the funeral on television, and the papers have been full of nothing else. The provisional government, however, sensing a possible uprising in the wake of the king's death, undertakes a massive deception. Everyone is told that the king did not really die. It was, or so say the media, an elaborate hoax perpetrated by enemies of the state. As a clincher the king appears on television to assure the people that (what else?) reports of his death were greatly exaggerated. This, of course, is a carefully doctored tape from one of the king's earlier press conferences. Everyone but Clyde gets the message and they reverse themselves. They all now believe that the king is alive and well. Clyde, however, has been cloistered in his study working on his thesis. He has seen no newspapers, watched no television, and talked to no one. He still believes the king is dead, and he believes it on the same grounds that everyone (originally) had for believing this (at the time they all knew the king was dead). When he emerges from his seclusion, strikes up a conversation with his barber, and promptly gets into an argument about whether or not the king is dead, what shall we say? Does Clyde (prior to exposure to the misleading counterevidence) know that the king is dead? Does he alone know something that other reasonable people ceased to believe days ago? Some say yes. Others say no. Since we don't want to pin anything on an example about which opinion appears to be divided, we leave it to others to judge this case. There are other examples that are more compelling, and these other examples raise what we feel are deep and puzzling questions about the nature of memory. Suppose Clyde has two friends, R (Reliable) and D (Deceiver), with whose trustworthiness, or lack of it, Clyde is familiar. Clyde knows that R's veracity is unimpeachable and that D often shades the truth when it suits his purposes. It is of the utmost importance that Clyde find out whether the enemy plans to attack and, as it turns out, both R and D have this information. Clyde asks R and is told that the enemy does indeed plan to attack. R's credibility, and Thought (Princeton, N. J.: Princeton University Press, 1973), p. 143. Harman uses this example, and others, to argue for a point about evidence one does not possess.
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knowledgeability about the enemy, is such that this communication is sufficient to convey knowledge to someone, like Clyde, familiar with R's trustworthiness. We are here taking for granted the possibility of such testimonial knowledge. Clyde now knows that the enemy plans to attack. He scribbles this valuable piece of information in his notebook and, exhausted from the day's work, drops off to sleep. He awakens in the morning, remembers what he learned the night before but finds himself unable to remember where he learned it. He knows he got it from either R or D (these are the only two people he talked to yesterday) but, try as he might, he cannot remember which one it was. He still believes that the enemy plans to attack since (he reasons) it is unlikely he would have written such a thing in his special notebook unless it came from a trusted source (i.e., R). Still, he would feel better about passing this important piece of information along to the chief of staff if he could actually remember getting it from R. Does Clyde still (in the morning) know that the enemy plans to attack? The belief he acquired the night before is still there. It was originally (last night) a piece of knowledge. O n something like a Causal Theory of Memory this (morning) belief should, it seems, qualify as a piece of memory knowledge. It has the right etiology. Yet, barring Clyde's coming to know (once again) by the indirect process of inference from his present belief and unwillingness to believe unreliable informants, it seems odd to say that Clyde knows the enemy plans to attack when he doesn't know whether he got this information from R or D. It may be that this example is still not quite what we are after. Realistically, it may be said, Clyde's inability to remember who told him about the enemy plans would affect his willingness to believe, surely his degree of confidence, that the enemy was planning to attack. Thus, we have not succeeded in giving an example where the belief is unaffected by the removal of its epistemic credentials. This can be rectified easily enough. We can either suppose that, upon awakening, Clyde doesn't realize that he has forgotten the source of his information (thus retaining, with the original degree of confidence, the belief that the enemy plans to attack) or that Clyde considers both R and D reliable informants (though, as before, only R is reliable). Hence, when Clyde awakens in the morning and can remember only that he got the information from either R or D, this does not shake his confideilce in the least. He considers both absolutely trustworthy and he knows he got it from one of them. Clyde's inability to remember whom he talked to leaves his belief
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without the requisite epistemic certification. He has lost what he needed in order to know. This, we think, is clear on intuitive grounds. But if one needs an argument for this judgment, we suggest taking one's favorite analysis of knowledge and asking what it says about Clyde's cognitive condition in the morning. For example, a justificationalist (knowledge = some form of justified true belief) must surely concede that Clyde has lost the crucial piece of information (it was R that told him) that (last night) justified his belief that the enemy planned to attack. If it hasn't been replaced by any comparable justification (as we are assuming), then, according to this account, Clyde no longer knows.' Even a Reliability Theorist (knowledge = a belief generated by some reliable process) is forced to make the same judgment. For the process by means of which Clyde acquired his belief (about the enemy plans) is either to be described as:
( P I )Told by a trusted informant in which case the process, not being reliable (D is also a trusted informant), does not yield knowledge, or it is to be described as: (P2) Told by R
in which case the process, though perfectly reliable, is one that Clyde, having forgotten who told him, is unable to tell is the process by means of which he acquired his belief. As such, the Reliabilist cannot invoke it as a knowledge-conferring process. To do so would be to trivialize the reliability condition. For every belief is generated by some process, and a n y process yielding a true belief can be rendered reliable (trivially) by the device of including the condition believed to obtain in a description of the process by means of which this belief is generated. Suppose, for example, that Clyde (last night) got his information from R in the form of a typed note slipped under his door. T h e note could as easily have come from D. This process, culminating in Clyde's belief that the enemy plans to attack, can easily be described in such a way as to make it (so described) reliable: uiz., receiving a note from R about the enemy plans or (a complete trivialization) receiving a note from someone when the enemy plans to attack. T h e reason these "proc'\Z7e are not claiming that whenever you forget how you learned that P, you thereby cease to know that P. Il'e are not, in other ~vords,taking issue with George Pappas' general point that one can lose one's justification without, thereby, losing one's knowledge (see his "Lost Justification," Midwest Studzes i n Philosophy, Vol. v, French, Uehling and \Z1ettstein (eds.), Minneapolis, 1980): 127-134. But this case (and others like it), we are claiming, is different. \Z'e return to this point later.
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esses" d o not confer knowledge, even though completely reliable,3 is that Clyde has n o way of telling that these, i n fact, are the processes by means of which his belief was generated. And this, we submit, is exactly Clyde's position the morning after he talks to R. Hence, he n o longer knows. A word should perhaps be said about a judgment that figures in this example. We supposed that when Clyde got the information about the enemy plans from R, a person he knew to be absolutely trustworthy, that he (then) knew that the enemy planned to attack. T h e fact that he also falsely believed D to be reliable does not affect R's ability to inform Clyde of what the enemy is u p to. This seems to us the correct way to judge the case. If it were otherwise, then one deceptive (or ignorant) teacher, a person the students thought as trustworthy as their other teachers, would render them incapable of learning (coming to know) anything from any of their teachers n o matter h o w trustworthy and well-informed these other teachers were. One bad apple would spoil the whole bunch just by being in the barrel with them. But bad apples cannot have ruined a n apple that is k n o w n to be good; a n d Clyde (we are supposing) k n o w s R to be reliable a n d k n o w s R told him that the enemy plans to attack. You can't get better apples than that. We seem then to have a genuine case where a belief, without altering its doxastic status, loses its epistemic certification and ceases to be knowledge. T o deny this is to embrace a peculiar asymmetry i n the life cycle of knowledge. For it was, presumably, the original justification (relating to the known reliability of the informant) that transformed Clyde's belief that the enemy planned to attack into a piece of knowledge. Since this justification has been lost, something else would have to play this supporting role if the belief was to continue its career as knowledge. But there is n o new means of support. There is simply the continued existence of the belief, a belief that at some earlier stage of its career was knowledge. Unless one is prepared (as we are not) to say that the epistemic status (as knowledge) of a belief is hereditary, that there is some principle of cognitive inertia (once a belief acquires a n epistemic momentum, it retains it even after removal of its cognitive impetus), it seems that this type of case must be taken to show that the relationship that converts a belief into knowledge is a n extrinsic relationship: a belief can acquire it (thereby becoming knowledge) or lose it (thereby 3 h t least the): are reliable i n the sense that such processes w o u l d n o t generate the belief that t h e e n e m y planned t o attack unless, i n fact, the e n e m y planned t o attack.
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ceasing to be knowledge) without altering in the slightest its identity as a belief. If we accept this conclusion, though, we are driven to paradoxical consequences. In describing Clyde's situation we endorsed the following three statements: (1) Clyde (last night) learned (hence, knew) that the enemy plans to attack. (2) Clyde (this morning) no longer knows that the enemy plans to attack. (3) Clyde (throughout this interval) believes that the enemy plans to attack. Assuming that factual memory (remembering that P) implies knowledge (knowing that P), (2) implies that Clyde does not remember that the enemy plans to attack. Since he knew it yesterday, but cannot remember it today, it seems correct to say that he has forgotten it.4 Yet, this seems to contradict (3). Can we really say that Clyde has forgotten what the enemy plans to do when, in the morning, he promptly reports their plans to attack to his superiors, insists that he knows this to be true, is (as it turns out) absolutely right in what he claims to know, and laughs at the suggestion that he has, quite without realizing it, forgotten this fact. He will doubtless insist (quite correctly in at least one sense of this ambiguous phrase) that he hasn't forgotten what he was told though he has forgotten who told it to him. How are we to describe this case? Shall we say that Clyde has forgotten that the enemy plans to attack and distinguish this way (or sense?) of forgetting from the (more usual?) way of forgetting that involves a loss of belief? Normally, "I forgot your birthday" or "I forgot that yesterday was your birthday" implies that the speaker did not (yesterday, or whenever the relevant time of action occurred) think or belzeue that it (yesterday) was your birthday. But perhaps we should distinguish this way of forgetting someone's birthday from a way of forgetting that is consistent with sending flowers on the appropriate day, organizing a timely surprise party, 41t is correct to say that he has forgotten it if a n inability to remember what you formerly knew is sufficient for forgetting. Dennis Stampe has made us less confident that this is sufficient. Still, nothing Jve say in this paper depends on its being true to say that Clyde has forgotten that the enemy plans to attack. It is enough (for us) if he does not remember that the enemy plans to attack. If the reader finds what Jve have to say about forgetting just too bizarre, Jve suggest a substitution of "does not remember" for every occurrence of "forget." tVe don't think this helps much, but some may find it less offensive.
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and so on. In this latter case the person forgets the birthday because he does not remember that it is your birthday and this, n o t because he does not think it is, but because he n o longer knows it is (having, like Clyde, forgotten h o w he found out). We might, for technical purposes, distinguish these two ways of forgetting by subscripts: forgettingB (= forgetting by losing the relevant belief) and forgettingE (= forgetting by loss of the appropriate epistemic relation for the continued belief). T h e latter strategy (the strategy, namely, of distinguishing different ways of forgetting) has some independent motivation. Whenever there are several necessary conditions for being an X, the denial that something is X will be ambiguous and, as a result, possibly misleading. W h i c h of the (several) necessary conditions does the thing in question fail to meet? If nothing more is said than that the thing is n o t X, one is left to infer that the condition (or conditions) typically unsatisfied is (are), in this case, also unsatisfied. Normally (in school, for example) when a teacher says that Sally doesn't know the answer to the problem, she means that Sally cannot c o m e up with the answer-does not believe that 79 is the answer-rather than that Sally gives 79 as the answer but cannot support it in a way that would demonstrate knowledge. Yet, since we all believe that coming u p with the right answer is not the same as knowing the answer, it would be quite true to say that Sally didn't know the answer even if she came up w i t h it (the correct answer) if she could adduce nothing in support of her belief that it was the right answer. Nevertheless, since "failure to come u p with the right answer" is the usual way of not knowing the answer (in school at least) the simple denial that Sally knows the answer will suggest that she can't come u p with it. And so it may be with memory and forgetting. T o say that Clyde has forgotten that the enemy will attack, can't remember whether they will or not, will suggest, unless further explanation is forthcoming, that he no longer believes that they will. It will suggest this because this is the typical way of forgetting such things. Nevertheless, if, as in Clyde's case, he has forgotten his source for this information, it will still be true to say that he has forgotten even if h e still believes ( a n d t h i n k s h e k n o w s ) t h a t t h e y p l a n t o attack. This, we suggest, is the explanation for the appearance of paradox associated with saying, "Clyde has forgotten that the enemy plans to attack" when he reports, accurately, to his superiors and insists that he (still) knows they plan to attack. And the same can be said about the person who, despite sending flowers and a card on your birthday, has forgotten (i.e., forgottenE) your birthday.
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Where does this leave us? Not, it must be confessed, in a n altogether comfortable position.5 For we now seem forced to accept the idea that whether or not a memory belief is still knowledge (whether or not it qualifies as a remembering-that) depends, not simply o n whether it began its (uninterrupted) career as knowledge, but o n whether there is a retention, in memory, of its evidential support. T h a t is, S's remembering P depends, not simply on the etiology of his belief that P, but o n whether or not he remembers Q for some value of Q. T h e "storage" metaphor suggested by the computer (and Plato's aviary) model of cognitive processes is misleading. Whether Clyde remembers that the enemy plans to attack depends on whether he remembers that it was R that told him this. If, in the circumstances envisaged, he forgets (= forgetsB) the latter fact, then, though he remains confident that the enemy plans to attack, he nonetheless promptly forgets (= forgets, = ceases to remember,) this fact also. It seems, then, that a general theory of knowledge must distinguish the belief acquisition process from the belief preseruation process. T o learn (= come to know) is to acquire a n enriched belief. Memory, in so far as it involves a retention of knowledge,6 is not simply the preservation of a suitably acquired belief, it is the suitable preservation of a suitably acquired belief. But what constitutes "suitable" preservation? If Clyde's first belief (the enemy plans to attack) is not suitably preserved unless his second belief ( R told me this) is preserved, what makes this latter belief a piece of knowledge? What makes its preservation suitable? Must Clyde remember what it was about R that "told" him it was R (and not, say, D) in order to remember that it was R who told him this? Where does this end? In foundations, of course. But we prefer not to grub around in the basement of knowledge. For it seems to us that whatever one wants to say about what makes a belief acquisition process suitable (one that yields knowledge), exactly the same thing must be said about the belief preservation process. Think of memory as a proc5Uncomfortable as this position may be, the alternative (described in "A Cognitive Cul-de-sac") seems, at least to one of us, even more uncomfortable. It involves abandoning the principle that one can know the known consequences of what one knows. Not all memory involves the retention of knowledge. So-called personal memory (remembering being kidnapped as a child) does not imply knowledge. One can remember being kidnapped as a child but, taking it to be a recurring fantasy, not realize that (hence, not know that; hence, not remember that) one actually was kidnapped as a child. See Don Locke's Memory (Garden City, N.J.: Doubleday, 1971), p. 75.
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ess in which one's earlier self "talks" to one's later self. One's later (ostensible memory) beliefs are the testimony of one's earlier self to one's later self. T h e question is: are these "testimonials" trustworthy? Are they the kind of guide that would, were this a belief acquisition process, give one knowledge about the matters whereof they speak? For a justificationalist this question is merely a way of asking whether one's present belief (about the past)-that is, the fact that one has this belief-constitutes a sufficient (for knowledge) justification of what one (therein) believes about the past. For a reliabilist the question is merely a way of asking about the reliability of these beliefs about the past-whether one would have them if they weren't true. Is this communication from one's past self like hearing something from R? Or is it more like talking to D? Is the acquisition-preservation process such as to filter out most (all?) false beliefs? Or, more realistically, is it such as to filter out most (all?) false beliefs of this sort? Once we look at Clyde's situation i n these terms, it seems clear that the testimony of his earlier self is not reliable, does not qualify as a n adequate justification, unless it includes the belief that R told h i m . Even then it may not be reliable. It depends o n whether Clyde's (morning) belief that R told him is itself reliably correlated with R's having told him. T h a t is to say, assuming R to be a perfectly reliable informant, Clyde's morning belief that R told him about the enemy plans will be a reliable index to the enemy's actual plans if Clyde's morning belief that it was R that told him this is itself a reliable index to R's having told him. If it isn't (Clyde often, or sometimes, confuses R and D in his memory), then to achieve the requisite level of reliability Clyde's morning beliefs will have to be even more specific. It may be necessary, for example, for him to believe, not only that R told him about the enemy plans, but that he told him this in their secret meeting place, a meeting place that only he and R know about. Now this belief may be perfectly reliable. Clyde never believes-not, at least, one day laterthat he met R in their secret meeting place without, in fact, having met R there. If this is the correct way to think about our knowledge of the past (and, we remind the reader, most of our knowledge is knowledge of the past), there are some lessons to be learned. We conclude by mentioning the most obvious. T h e suitability of a belief preservation process is, among other things, a function of the content, complexity, and interconnectedness of the beliefs being preserved. T h e richer and more interconnected one's system of beliefs about the past, the more likely it is
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that the elements of this system (the i n d i v i d ~ ~ abeliefs) l have been properly cared for and, thus, qualify as knowledge. T h e more likely it is, in other words, that one really remembers. Clyde may not remember that the enemy plans to attack if this is all he finds himself believing the next morning, but his chances of actually remembering this are substantially increased if he finds himself believing, not only that the enemy plans to attack, but that he got this information from R and the communication occurred at their secret meeting place. This, we think, is fairly obvious. The more "texture" there is to our memory beliefs, the more confidence they inspire.' The belief acquisition process exhibits a similar property. A newspaper (magazine, person) may not be trustworthy in reporting, say, that there are a lot of drugs on campus. They tend to say that sort of thing, even when it isn't true, to sell more papers. Nevertheless, they may be absolutely trustworthy in reporting the details. You know there are drugs on campus when they report that Smith, the Dean's secretary, sold 2 pounds of cocaine to Brown, the basketball coach, in the Dean's office on Homecoming Weekend. They don't say that kind of thing unless it is true and they can back it up. Secondly, the question of whether the belief preservation process is reliable or not and, hence, whether one genuinely remembers (= knows) what one finds oneself believing about the past depends not just on the believer, what he believes, and the mechanisms by means of which these beliefs are acquired, stored, and retrieved. It also depends on the kinds of "forces," both internal and external, that are operating to expose false beliefs. Whether or not my belief that Lincoln was our Civil War president is reliable (despite my inability to remember where I first learned this) is a function of how it fits in with the many other beliefs I have about American history (internal force) and how it withstands the dissolving influence of what I hear from others. Beliefs about public events must, in other words, endure an obstacle course in order to survive, and this obstacle course acts as a filter in eliminating false beliefs. Compare my belief about Lincoln with my belief that I stubbed my toe while playing alone in my room on my seventh birthday. This latter belief, though preserved as faultlessly as my belief about Lincoln, 'There is, of course, a correspondence between the "texture" of a memory belief and the recency of its acquisition. T h e more recent it is, the more "vivid" and "detailedu-hence, the more reliable. At a certain point (short term memory?), it may be incoherent to expect a "proof" that the memory is reliable (or that such memories are i n general reliable) since any "proof" will itself presuppose the reliability of (at least short term) memory.
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will not thereby be as reliable. It is protected from the kind of forces that operate on the Lincoln belief. No one else is in a position to challenge me about my solitary activities on my seventh birthday and my toe-stubbing doesn't "hang together" in my memory with any other belief I have about that day. As a consequence, I may well remember that Lincoln was our Civil War president and not remember (though still, of course, believing) that I stubbed my toe on my seventh birthday despite the equal care both beliefs received since acquisition. One could, of course, diminish the reliability of the Lincoln belief by refusing to learn any (more) American history and by refusing to listen to anyone talk about this period. A more practical alternative would be to simply retire to a deserted island and live in splendid isolation. This belief might then lose the kind of reliability it enjoyed i n a more dynamic setting. One would cease to know, n o longer remember, forget (forgetE) that Lincoln was the Civil War president. It is, we submit, harder to remember things when you live alone in a cave.' Finally, this picture of knowledge and memory exhibits the division of labor that exists between the acquisition and preservation processes. The more cautious one is about the beliefs one acquires (the greater burden one puts on the acquisition process) the less work one's memory has to do to preserve the knowledge so acquired. The more gullible one is during the acquisition phase, the greater memory resources must be devoted to preserving whatever knowledge is acquired. Though Clyde's brother learns exactly what Clyde learns from his conversations with R (namely, that the enemy plans to attack), his brother, being a much more cautious fellow (he doesn't trust D) needn't, like Clyde, remember who told him about the enemy plans ( R or D) in order to remember that the enemy plans to attack. If he is aware of his own caution in this regard, he can reconstruct this fact, but the point is that the belief that R told him need n o t be preserved in m e m o r y for him to continue knowing something that Clyde can only continue knowing by remembering who told him. The conclusion seems to be that 'There are a variety of "suitable" belief preservation processes. Knowing one's own reliability as an acquirer of that kind of belief may enter the picture (on a justificationalist's account of memory knowledge it will certainly enter the picture). There is in principle n o limit to the kind of preservation process one might exploit. But the situation is not symmetric with regard to the acquisition process. No belief, n o matter how well preserved, qualifies as a memory (a remembering-that) unless it has the right etiology. T h e etiology of suitably preserved beliefs (i.e., their suitable acquisition) is what makes them memorzes.
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the gullible may learn as much as their more critical colleagues, but they need a much better memory to keep it. FRED DRETSKE PALLE YOURGRAU
University of Wisconsin/Madison
BOOK REVIEWS
T h e Enterprise of Knowledge: An Essay o n Knowledge, Credal Probability and Chance. ISAAC LEVI Cambridge, Mass.: MIT Press, 1980. XVII,462 p. $27.50. T h e corpus of knowledge According to Levi the corpus of claims an agent is committed to accept as his present body of knowledge functions as his standard for what counts as a serious possibility in formulating decision problems and guiding enquiry. This pragmatic view of the role of knowledge as a resource for guiding decision and enquiry underlies Levi's laudible distinction between certainty and incorrigibility. If an agent accepts some claim as part of his standard for serious possibility then he does not now regard it as seriously possible that this claim is false. Certainty is a constituitive feature of the role of accepted knowledge claims as one's standard for serious possibility. Corrigibility, on the other hand, results from one's policies for updating what he accepts, as his epistemic circumstances change. On Levi's model it can be rational for me to be certain that some Argentinians invaded the Falklands in 1982 even though I have in place epistemic policies that would lead me to give up this claim were I to be confronted with enough of the right sort of surprises in the future. It seems to me that Levi is exactly right on this point and that getting this right is important for understanding the practices that constitute our use of knowledge. It also seems to me that Levi's case for this point would have been better presented without his rhetoric about pedigree epistemology. Levi represents the corpus an agent is committed to accept at a given time by a logically closed set of sentences of some appropriate language. He distinguishes a subset of the corpus which is to 0022-302X/83/8006/0367$01 .OO
0 1983 The Journal of Philosophy, Inc.
