by D Lewis · 1996 · Cited by 2022 — We know a lot. I know what food penguins eat. I know that phones used to ring, but nowadays squeal, when someone calls up. I know that Essendon won the 1993
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Australasian Journal of Philosophy Vol. 74, No. 4; December 1996 ELUSIVE KNOWLEDGE” David Lewis We know a lot. I know what food penguins eat. I know that phones used to ring, but nowadays squeal, when someone calls up. I know that Essendon won the 1993 Grand Final. I know that here is a hand, and here is another. We have all sorts of everyday knowledge, and we have it in abundance. To doubt that would be absurd. At any rate, to doubt it in any serious and lasting way would be absurd; and even philosophical and temporary doubt, under the influence of argument, is more than a little peculiar. It is a Moorean fact that we know a lot. It is one of those things that we know better than we know the premises of any philosophical argument to the contrary. Besides knowing a lot that is everyday and trite, I myself think that we know a lot that is interesting and esoteric and controversial. We know a lot about things unseen: tiny particles and pervasive fields, not to mention one another’s underwear. Sometimes we even know what an author meant by his writings. But on these questions, let us agree to disagree peacefully with the champions of ‘post-knowledgeism’. The most trite and ordinary parts of our knowledge will be problem enough. For no sooner do we engage in epistemology – the systematic philosophical examination of knowledge – than we meet a compelling argument that we know next to nothing. The sceptical argument is nothing new or fancy. It is just this: it seems as if knowledge must be by definition infallible. If you claim that S knows that P, and yet you grant that S can- not eliminate a certain possibility in which not-P, it certainly seems as if you have granted that S does not after all know that P. To speak of fallible knowledge, of knowl- edge despite uneliminated possibilities of error, just sounds contradictory. Blind Freddy can see where this will lead. Let your paranoid fantasies rip – CIA plots, hallucinogens in the tap water, conspiracies to deceive, old Nick himself- and soon you find that uneliminated possibilities of error are everywhere. Those possibilities of error are far-fetched, of course, but possibilities all the same. They bite into even our most everyday knowledge. We never have infallible knowledge. Never – well, hardly ever. Some say we have infallible knowledge of a few simple, axiomatic necessary truths; and of our own present experience. They say that I simply cannot be wrong that a part of a part of something is itself a part of that thing; or that it seems to me now (as I sit here at the keyboard) exactly as if I am hearing clicking noises on top of a steady whirring. Some say so. Others deny it. No matter; let it be granted, at least for the sake of the argument. It is not nearly enough. If we have only that much Thanks to many for valuable discussions of this material. Thanks above all to Peter Unger; and to Stewart Cohen, Michael Devitt, Alan Hajek, Stephen Hetherington, Denis Robinson, Ernest Sosa, Robert Stalnaker, Jonathan Vogel, and a referee for this Journal. Thanks also to the Boyce Gibson Memorial Library and to Ormond College. 549 Downloaded By: [Ingenta Content Distribution – Routledge] At: 09:32 20 January 2009Australasian Journal of Philosophy Vol. 74, No.4; December 1996 ELUSIVE KNOWLEDGE’ David Lewis We know a lot. I know what food penguins eat. I know that phones used to ring, but nowadays squeal, when someone calls up. I know that Essendon won the 1993 Grand Final. I know that here is a hand, and here is another. We have all sorts of everyday knowledge, and we have it in abundance. To doubt that would be absurd. At any rate, to doubt it in any serious and lasting way would be absurd; and even philosophical and temporary doubt, under the influence of argument, is more than a little peculiar. It is a Moorean fact that we know a lot. It is one of those things that we know better than we know the premises of any philosophical argument to the contrary. Besides knowing a lot that is everyday and trite, I myself think that we know a lot that is interesting and esoteric and controversial. We know a lot about things unseen: tiny particles and pervasive fields, not to mention one another’s underwear. Sometimes we even know what an author meant by his writings. But on these questions, let us agree to disagree peacefully with the champions of ‘post-knowledgeism’. The most trite and ordinary parts of our knowledge will be problem enough. For no sooner do we engage in epistemology -the systematic philosophical examination of knowledge -than we meet a compelling argument that we know next to nothing. The sceptical argument is nothing new or fancy. It is just this: it seems as if knowledge must be by definition infallible. If you claim that S knows that P, and yet you grant that S not eliminate a certain possibility in which not-P, it certainly seems as if you have granted that S does not after all know that P. To speak of fallible knowledge, of edge despite uneliminated possibilities of error, just sounds contradictory. Blind Freddy can see where this will lead. Let your paranoid fantasies rip -CIA plots, hallucinogens in the tap water, conspiracies to deceive, old Nick himself -and soon you find that uneliminated possibilities of error are everywhere. Those possibilities of error are far-fetched, of course, but possibilities all the same. They bite into even our most everyday knowledge. We never have infallible knowledge. Never -well, hardly ever. Some say we have infallible knowledge of a few simple, axiomatic necessary truths; and of our own present experience. They say that I simply cannot be wrong that a part of a part of something is itself a part of that thing; or that it seems to me now (as I sit here at the keyboard) exactly as if I am hearing clicking noises on top of a steady whirring. Some say so. Others deny it. No matter; let it be granted, at least for the sake of the argument. It is not nearly enough. If we have only that much Thanks to many for valuable discussions of this material. Thanks above all to Peter Unger; and to Stewart Cohen, Michael Devitt, Alan Hajek, Stephen Hetherington, Denis Robinson, Ernest Sosa, Robert Stalnaker, Jonathan Vogel, and a referee for this Journal. Thanks also to the Boyce Gibson Memorial Library and to Ormond College. 549
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550 Elusive Knowledge infallible knowledge, yet knowledge is by definition infallible, then we have very little knowledge indeed – not the abundant everyday knowledge we thought we had. That is still absurd. So we know a lot; knowledge must be infallible; yet we have fallible knowledge or none (or next to none). We are caught between the rock of fallibilism and the whirlpool of scepticism. Both are mad! Yet fallibilism is the less intrusive madness. It demands less frequent corrections of what we want to say. So, if forced to choose, I choose fallibilism. (And so say all of us.) We can get used to it, and some of us have done. No joy there – we know that people can get used to the most crazy philosophical sayings imaginable. If you are a contented fallibilist, I implore you to be honest, be naive, hear it afresh. ‘He knows, yet he has not eliminated all possibilities of error.’ Even if you’ve numbed your ears, doesn’t this overt, explicit fallibilism still sound wrong? Better fallibilism than scepticism; but it would be better still to dodge the choice. I think we can. We will be alarmingly close to the rock, and also alarmingly close to the whirlpool, but if we steer with care, we can -just barely – escape them both. Maybe epistemology is the culprit. Maybe this extraordinary pastime robs us of our knowledge. Maybe we do know a lot in daily life; but maybe when we look hard at our knowledge, it goes away. But only when we look at it harder than the sane ever do in daily life; only when we let our paranoid fantasies rip. That is when we are forced to admit that there always are uneliminated possibilities of error, so that we have fallible knowledge or none. Much that we say is context-dependent, in simple ways or subtle ways. Simple: ‘it’s evening’ is truly said when, and only when, it is said in the evening. Subtle: it could well be true, and not just by luck, that Essendon played rottenly, the Easybeats played brilliantly, yet Essendon won. Different contexts evoke different standards of evalua- tion. Talking about the Easybeats we apply lax standards, else we could scarcely distinguish their better days from their worse ones. In talking about Essendon, no such laxity is required. Essendon won because play that is rotten by demanding standards suf- fices to beat play that is brilliant by lax standards. Maybe ascriptions of knowledge are subtly context-dependent, and maybe epistemol- ogy is a context that makes them go false. Then epistemology would be an investigation that destroys its own subject matter. If so, the sceptical argument might be flawless, when we engage in epistemology – and only then! 1 If you start from the ancient idea that justification is the mark that distinguishes knowledge from mere opinion (even true opinion), then you well might conclude that ascriptions of knowledge are context-dependent because standards for adequate justifica- tion are context-dependent. As follows: opinion, even if true, deserves the name of The suggestion that ascriptions of knowledge go false in the context of epistemology is to be found in Barry Stroud, ‘Understanding Human Knowledge in General’ in Marjorie Clay and Keith Lehrer (eds.), Knowledge and Skepticism (Boulder: Westview Press, 1989); and in Stephen Hetherington, ‘Lacking Knowledge and Justification by Theorising About Them’ (lec- ture at the University of New South Wales, August 1992). Neither of them tells the story just as I do, however it may be that their versions do not conflict with mine. Downloaded By: [Ingenta Content Distribution – Routledge] At: 09:32 20 January 2009550 Elusive Knowledge infallible knowledge, yet knowledge is by definition infallible, then we have very little knowledge indeed -not the abundant everyday knowledge we thought we had. That is still absurd. So we know a lot; knowledge must be infallible; yet we have fallible knowledge or none (or next to none). We are caught between the rock of fallibilism and the whirlpool of scepticism. Both are mad! Yet fallibilism is the less intrusive madness. It demands less frequent corrections of what we want to say. So, if forced to choose, I choose fallibilism. (And so say all of us.) We can get used to it, and some of us have done. No joy there -we know that people can get used to the most crazy philosophical sayings imaginable. If you are a contented fallibilist, I implore you to be honest, be naive, hear it afresh. ‘He knows, yet he has not eliminated all possibilities of error.’ Even if you’ve numbed your ears, doesn’t this overt, explicit fallibilism still sound wrong? Better fallibilism than scepticism; but it would be better still to dodge the choice. I think we can. We will be alarmingly close to the rock, and also alarmingly close to the whirlpool, but if we steer with care, we can -just barely -escape them both. Maybe epistemology is the culprit. Maybe this extraordinary pastime robs us of our knowledge. Maybe we do know a lot in daily life; but maybe when we look hard at our knowledge, it goes away. But only when we look at it harder than the sane ever do in daily life; only when we let our paranoid fantasies rip. That is when we are forced to admit that there always are uneliminated possibilities of error, so that we have fallible knowledge or none. Much that we say is context-dependent, in simple ways or subtle ways. Simple: ‘it’s evening’ is truly said when, and only when, it is said in the evening. Subtle: it could well be true, and not just by luck, that Essendon played rottenly, the Easybeats played brilliantly, yet Essendon won. Different contexts evoke different standards of tion. Talking about the Easybeats we apply lax standards, else we could scarcely distinguish their better days from their worse ones. In talking about Essendon, no such laxity is required. Essendon won because play that is rotten by demanding standards fices to beat play that is brilliant by lax standards. Maybe ascriptions of knowledge are subtly context-dependent, and maybe ogy is a context that makes them go false. Then epistemology would be an investigation that destroys its own subject matter. If so, the sceptical argument might be flawless, when we engage in epistemology -and only then” If you start from the ancient idea that justification is the mark that distinguishes knowledge from mere opinion (even true opinion), then you well might conclude that ascriptions of knowledge are context-dependent because standards for adequate tion are context-dependent. As follows: opinion, even if true, deserves the name of The suggestion that ascriptions of knowledge go false in the context of epistemology is to be found in Barry Stroud, ‘Understanding Human Knowledge in General’ in Marjorie Clay and Keith Lehrer (eds.), Knowledge and Skepticism (Boulder: Westview Press, 1989); and in Stephen Hetherington, ‘Lacking Knowledge and Justification by Theorising About Them’ ture at the University of New South Wales, August 1992). Neither of them tells the story just as I do, however it may be that their versions do not conflict with mine.
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David Lewis 551 knowledge only if it is adequately supported by reasons; to deserve that name in the especially demanding context of epistemology, the arguments from supporting reasons must be especially watertight; but the special standards of justification that this special context demands never can be met (well, hardly ever). In the strict context of epistemol- ogy we know nothing, yet in laxer contexts we know a lot. But I myself cannot subscribe to this account of the context-dependence of knowl- edge, because I question its starting point. I don’t agree that the mark of knowledge is justification. 2 First, because justification is not sufficient: your true opinion that you will lose the lottery isn’t knowledge, whatever the odds. Suppose you know that it is a fair lottery with one winning ticket and many losing tickets, and you know how many losing tickets there are. The greater the number of losing tickets, the better is your justi- fication for believing you will lose. Yet there is no number great enough to transform your fallible opinion into knowledge – after all, you just might win. No justification is good enough – or none short of a watertight deductive argument, and all but the sceptics will agree that this is too much to demand? Second, because justification is not always necessary. What (non-circular) argument supports our reliance on perception, on memory, and on testimony? 4 And yet we do gain knowledge by these means. And sometimes, far from having supporting arguments, we don’t even know how we know. We once had evidence, drew conclusions, and thereby gained knowledge; now we have forgotten our reasons, yet still we retain our knowledge. Or we know the name that goes with the face, or the sex of the chicken, by relying on subtle visual cues, without knowing what those cues may be. The link between knowledge and justification must be broken. But if we break that link, then it is not – or not entirely, or not exactly – by raising the standards of justifica- tion that epistemology destroys knowledge. I need some different story. To that end, I propose to take the infallibility of knowledge as my starting point? Must infallibilist epistemology end in scepticism? Not quite. Wait and see. Anyway, here is the definition. Subject S knows proposition P iffP holds in every possibility left unelim- inated by S’s evidence; equivalently, iff S’s evidence eliminates every possibility in which not-P. The definition is short, the commentary upon it is longer. In the first place, there is the proposition, P. What I choose to call ‘propositions’ are individuated coarsely, by necessary equivalence. For instance, there is only one necessary proposition. It holds in 2 Unless, like some, we simply define ‘justification’ as ‘whatever it takes to turn true opinion into knowledge’ regardless of whether what it takes turns out to involve argument from supporting reasons. 3 The problem of the lottery was introduced in Henry Kyburg, Probability and the Logic of Rational Belief (Middletown, CT: Wesleyan University Press, 1961), and in Carl Hempet, ‘Deductive-Nomological vs. Statistical Explanation’ in Herbert Feigl and Grover Maxwell (eds.), Minnesota Studies in the Philosophy of Science, Vol. II (Minneapolis: University of Minnesota Press, 1962). It has been much discussed since, as a problem both about knowledge and about our everyday, non-quantitative concept of belief. 4 The case of testimony is less discussed than the others; but see C.A.J. Coady, Testimony: A PhilosophicalStudy (Oxford: Clarendon Press, 1992) pp. 79-129. 5 I follow Peter Unger, Ignorance: A Case for Skepticism (New York: Oxford University Press, 1975). But I shall not let him lead me into scepticism. Downloaded By: [Ingenta Content Distribution – Routledge] At: 09:32 20 January 2009David Lewis 551 knowledge only if it is adequately supported by reasons; to deserve that name in the especially demanding context of epistemology, the arguments from supporting reasons must be especially watertight; but the special standards of justification that this special context demands never can be met (well, hardly ever). In the strict context of ogy we know nothing, yet in laxer contexts we know a lot. But I myself cannot subscribe to this account of the context-dependence of edge, because I question its starting point. I don’t agree that the mark of knowledge is justification.2 First, because justification is not sufficient: your true opinion that you will lose the lottery isn’t knowledge, whatever the odds. Suppose you know that it is a fair lottery with one winning ticket and many losing tickets, and you know how many losing tickets there are. The greater the number of losing tickets, the better is your fication for believing you will lose. Yet there is no number great enough to transform your fallible opinion into knowledge -after all, you just might win. No justification is good enough -or none short of a watertight deductive argument, and all but the sceptics will agree that this is too much to demand.’ Second, because justification is not always necessary. What (non-circular) argument supports our reliance on perception, on memory, and on testimony?’ And yet we do gain knowledge by these means. And sometimes, far from having supporting arguments, we don’t even know how we know. We once had evidence, drew conclusions, and thereby gained knowledge; now we have forgotten our reasons, yet still we retain our knowledge. Or we know the name that goes with the face, or the sex of the chicken, by relying on subtle visual cues, without knowing what those cues may be. The link between knowledge and justification must be broken. But if we break that link, then it is not -or not entirely, or not exactly -by raising the standards of tion that epistemology destroys knowledge. I need some different story. To that end, I propose to take the infallibility of knowledge as my starting point.’ Must infallibilist epistemology end in scepticism? Not quite. Wait and see. Anyway, here is the definition. Subject S knows proposition P iff P holds in every possibility left inated by S’s evidence; equivalently, iff S’s evidence eliminates every possibility in which not-P. The definition is short, the commentary upon it is longer. In the first place, there is the proposition, P. What I choose to call ‘propositions’ are individuated coarsely, by necessary equivalence. For instance, there is only one necessary proposition. It holds in Unless, like some, we simply define ‘justification’ as ‘whatever it takes to tum true opinion into knowledge’ regardless of whether what it takes turns out to involve argument from supporting reasons. The problem of the lottery was introduced in Henry Kyburg, Probability and the Logic of Rational Belief (Middletown, CT: Wesleyan University Press, 1961), and in Carl Hempel, ‘Deductive-Nomological vs. Statistical Explanation’ in Herbert Feigl and Grover Maxwell (eds.), Minnesota Studies in the Philosophy of Science, Vol. II (Minneapolis: University of Minnesota Press, 1962). It has been much discussed since, as a problem both about knowledge and about our everyday, non-quantitative concept of belief. The case of testimony is less discussed than the others; but see CA.J. Coady, Testimony: A Philosophical Study (Oxford: Clarendon Press, 1992) pp. 79-129. I follow Peter Unger, Ignorance: A Case for Skepticism (New York: Oxford University Press, 1975). But I shall not let him lead me into scepticism.
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552 Elusive Knowledge every possibility; hence in every possibility left uneliminated by S’s evidence, no matter who S may be and no matter what his evidence may be. So the necessary proposition is known always and everywhere. Yet this known proposition may go unrecognised when presented in impenetrable linguistic disguise, say as the proposition that every even num- ber is the sum of two primes. Likewise, the known proposition that I have two hands may go unrecognised when presented as the proposition that the number of my hands is the least number n such that every even number is the sum of n primes. (Or if you doubt the necessary existence of numbers, switch to an example involving equivalence by logic alone.) These problems of disguise shall not concern us here. Our topic is modal, not hyperintensional, epistemology. 6 Next, there are the possibilities. We needn’t enter here into the question whether these are concreta, abstract constructions, or abstract simples. Further, we needn’t decide whether they must always be maximally specific possibilities, or whether they need only be specific enough for the purpose at hand. A possibility will be specific enough if it cannot be split into subcases in such a way that anything we have said about possibilities, or anything we are going to say before we are done, applies to some subcas- es and not to others. For instance, it should never happen that proposition P holds in some but not all sub-cases; or that some but not all sub-cases are eliminated by S’s evi- dence. But we do need to stipulate that they are not just possibilities as to how the whole world is; they also include possibilities as to which part of the world is oneself, and as to when it now is. We need these possibilities de se et nunc because the propositions that may be known include propositions de se et nunc. 7 Not only do I know that there are hands in this world somewhere and somewhen. I know that I have hands, or anyway I have them now. Such propositions aren’t just made true or made false by the whole world once and for all. They are true for some of us and not for others, or true at some times and not others, or both. Further, we cannot limit ourselves to ‘real’ possibilities that conform to the actual laws of nature, and maybe also to actual past history. For propositions about laws and history are contingent, and may or may not be known. Neither can we limit ourselves to ‘epistemic’ possibilities for S – possibilities that S does not know not to obtain. That would drain our definition of content. Assume only that knowledge is closed under strict implication. (We shall consider the merits of this assumption later.) Remember that we are not distinguishing between equivalent proposi- tions. Then knowledge of a conjunction is equivalent to knowledge of every conjunct. P is the conjunction of all propositions not-W, where W is a possibility in which not-P. That suffices to yield an equivalence: S knows that P iff, for every possibility W in which not-P, S knows that not-W. Contraposing and cancelling a double negation: iff every possibility which S does not know not to obtain is one in which P. For short: iffP holds throughout S’s epistemic possibilities. Yet to get this far, we need no substantive definition of knowledge at all! To turn this into a substantive definition, in fact the very definition we gave before, we need to say one more thing: S’s epistemic possibilities are 6 See Robert Stalnaker, Inquiry (Cambridge, MA: MIT Press, 1984) pp. 59-99. 7 See my ‘Attitudes De Dicto and De Se’, The Philosophical Review 88 (1979) pp. 513-543; and R.M. Chisholm, ‘The Indirect Reflexive’ in C. Diamond and J. Teichman (eds.), Intention and Intentionality: Essays in Honour of G.E.M. Anscombe (Brighton: Harvester, 1979). Downloaded By: [Ingenta Content Distribution – Routledge] At: 09:32 20 January 2009552 Elusive Knowledge every possibility; hence in every possibility left uneliminated by S’s evidence, no matter who S may be and no matter what his evidence may be. So the necessary proposition is known always and everywhere. Yet this known proposition may go unrecognised when presented in impenetrable linguistic disguise, say as the proposition that every even ber is the sum of two primes. Likewise, the known proposition that I have two hands may go unrecognised when presented as the proposition that the number of my hands is the least number n such that every even number is the sum of n primes. (Or if you doubt the necessary existence of numbers, switch to an example involving equivalence by logic alone.) These problems of disguise shall not concern us here. Our topic is modal, not hyperintensional, epistemology. 6 Next, there are the possibilities. We needn’t enter here into the question whether these are concreta, abstract constructions, or abstract simples. Further, we needn’t decide whether they must always be maximally specific possibilities, or whether they need only be specific enough for the purpose at hand. A possibility will be specific enough if it cannot be split into sub cases in such a way that anything we have said about possibilities, or anything we are going to say before we are done, applies to some es and not to others. For instance, it should never happen that proposition P holds in some but not all sub-cases; or that some but not all sub-cases are eliminated by S’s dence. But we do need to stipulate that they are not just possibilities as to how the whole world is; they also include possibilities as to which part of the world is oneself, and as to when it now is. We need these possibilities de se et nunc because the propositions that may be known include propositions de se et nunc.’ Not only do I know that there are hands in this world somewhere and somewhen. I know that I have hands, or anyway I have them now. Such propositions aren’t just made true or made false by the whole world once and for all. They are true for some of us and not for others, or true at some times and not others, or both. Further, we cannot limit ourselves to ‘real’ possibilities that conform to the actual laws of nature, and maybe also to actual past history. For propositions about laws and history are contingent, and mayor may not be known. Neither can we limit ourselves to ‘epistemic’ possibilities for S – possibilities that S does not know not to obtain. That would drain our definition of content. Assume only that knowledge is closed under strict implication. (We shall consider the merits of this assumption later.) Remember that we are not distinguishing between equivalent tions. Then knowledge of a conjunction is equivalent to knowledge of every conjunct. P is the conjunction of all propositions not-W, where W is a possibility in which not-Po That suffices to yield an equivalence: S knows that P iff, for every possibility W in which not-P, S knows that not-W. Contraposing and cancelling a double negation: iff every possibility which S does not know not to obtain is one in which P. For short: iff P holds throughout S’s epistemic possibilities. Yet to get this far, we need no substantive definition of knowledge at all! To turn this into a substantive definition, in fact the very definition we gave before, we need to say one more thing: S’s epistemic possibilities are See Robert Stalnaker, Inquiry (Cambridge, MA: MIT Press, 1984) pp. 59-99. See my ‘Attitudes De Dicto and De Se’, The Philosophical Review 88 (1979) pp. 513-543; and R.M. Chisholm, ‘The Indirect Reflexive’ in C. Diamond and 1. Teichman (eds.), Intention and Intentionality: Essays in Honour of G.E.M. Anscombe (Brighton: Harvester, 1979).
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David Lewis 553 just those possibilities that are uneliminated by S’s evidence. So, next, we need to say what it means for a possibility to be eliminated or not. Here I say that the uneliminated possibilities are those in which the subject’s entire perceptual experience and memory are just as they actually are. There is one possibility that actual- ly obtains (for the subject and at the time in question); call it actuality. Then a possibility W is uneliminated iff the subject’s perceptual experience and memory in W exactly match his perceptual experience and memory in actuality. (If you want to include other alleged forms of basic evidence, such as the evidence of our extrasensory faculties, or an innate disposition to believe in God, be my guest. If they exist, they should be included. If not, no harm done if we have included them conditionally.) Note well that we do not need the ‘pure sense-datum language’ and the ‘incorrigible protocol statements’ that for so long bedevilled foundationalist epistemology. It matters not at all whether there are words to capture the subject’s perceptual and memory evi- dence, nothing more and nothing less. If there are such words, it matters not at all whether the subject can hit upon them. The given does not consist of basic axioms to serve as premises in subsequent arguments. Rather, it consists of a match between possi- bilities. When perceptual experience E (or memory) eliminates a possibility W, that is not because the propositional content of the experience conflicts with W. (Not even if it is the narrow content.) The propositional content of our experience could, after all, be false. Rather, it is the existence of the experience that conflicts with W: W is a possibili- ty in which the subject is not having experience E. Else we would need to tell some fishy story of how the experience has some sort of infallible, ineffable, purely phenome- nal propositional content Who needs that? Let E have propositional content P. Suppose even – something I take to be an open question – that E is, in some sense, fully characterized by P. Then I say that E eliminates W iff W is a possibility in which the subject’s experience or memory has content different from P. I do not say that E elimi- nates W iff W is a possibility in which P is false. Maybe not every kind of sense perception yields experience; maybe, for instance, the kinaesthetic sense yields not its own distinctive sort of sense-experience but only sponta- neous judgements about the position of one’s limbs. If this is true, then the thing to say is that kinaesthetic evidence eliminates all possibilities except those that exactly resem- ble actuality with respect to the subject’s spontaneous kinaesthetic judgements. In saying this, we would treat kinaesthetic evidence more on the model of memory than on the model of more .typical senses. Finally, we must attend to the word ‘every’. What does it mean to say that every pos- sibility in which not-P is eliminated? An idiom of quantification, like ‘every’, is normally restricted to some limited domain. If I say that every glass is empty, so it’s time for another round, doubtless I and my audience are ignoring most of all the glasses there are in the whole wide world throughout all of time. They are outside the domain. They are irrelevant to the truth of what was said. Likewise, if I say that every uneliminated possibility is one in which P, or words to that effect, I am doubtless ignoring some of all the uneliminated alternative possibilities that there are. They are outside the domain, they are irrelevant to the truth of what was said. Downloaded By: [Ingenta Content Distribution – Routledge] At: 09:32 20 January 2009David Lewis 553 just those possibilities that are uneliminated by S’s evidence. So, next, we need to say what it means for a possibility to be eliminated or not. Here I say that the uneliminated possibilities are those in which the subject’s entire perceptual experience and memory are just as they actually are. There is one possibility that ly obtains (for the subject and at the time in question); call it actuality. Then a possibility W is uneliminated iff the subject’s perceptual experience and memory in W exactly match his perceptual experience and memory in actuality. (If you want to include other alleged forms of basic evidence, such as the evidence of our extrasensory faculties, or an innate disposition to believe in God, be my guest. If they exist, they should be included. If not, no harm done if we have included them conditionally.) Note well that we do not need the ‘pure sense-datum language’ and the ‘incorrigible protocol statements’ that for so long bedevilled foundationalist epistemology. It matters not at all whether there are words to capture the subject’s perceptual and memory dence, nothing more and nothing less. If there are such words, it matters not at all whether the subject can hit upon them. The given does not consist of basic axioms to serve as premises in subsequent arguments. Rather, it consists of a match between bilities. When perceptual experience E (or memory) eliminates a possibility W, that is not because the propositional content of the experience conflicts with W. (Not even if it is the narrow content.) The propositional content of our experience could, after all, be false. Rather, it is the existence of the experience that conflicts with W: W is a ty in which the subject is not having experience E. Else we would need to tell some fishy story of how the experience has some sort of infallible, ineffable, purely nal propositional content. .. Who needs that? Let E have propositional content P. Suppose even -something I take to be an open question -that E is, in some sense, fully characterized by P. Then I say that E eliminates W iff W is a possibility in which the subject’s experience or memory has content different from P. I do not say that E nates W iff W is a possibility in which P is false. Maybe not every kind of sense perception yields experience; maybe, for instance, the kinaesthetic sense yields not its own distinctive sort of sense-experience but only neous judgements about the position of one’s limbs. If this is true, then the thing to say is that kinaesthetic evidence eliminates all possibilities except those that exactly ble actuality with respect to the subject’s spontaneous kinaesthetic judgements. In saying this, we would treat kinaesthetic evidence more on the model of memory than on the model of more typical senses. Finally, we must attend to the word ‘every’. What does it mean to say that every sibility in which not-P is eliminated? An idiom of quantification, like ‘every’, is normally restricted to some limited domain. If I say that every glass is empty, so it’s time for another round, doubtless I and my audience are ignoring most of all the glasses there are in the whole wide world throughout all of time. They are outside the domain. They are irrelevant to the truth of what was said. Likewise, if I say that every uneliminated possibility is one in which P, or words to that effect, I am doubtless ignoring some of all the uneliminated alternative possibilities that there are. They are outside the domain, they are irrelevant to the truth of what was said.
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554 Elusive Knowledge But, of course, I am not entitled to ignore just any possibility I please. Else true ascriptions of knowledge, whether to myself or to others, would be cheap indeed. I may properly ignore some uneliminated possibilities; I may not properly ignore others. Our definition of knowledge requires a sotto voce proviso. S knows that P iff S’s evidence eliminates every possibility in which not-/’ – Psst! – except for those possibilities that we are properly ignoring. Unger suggests an instructive parallel. 8 Just as P is known iff there are no unelimi- nated possibilities of error, so likewise a surface is fiat iff there are no bumps on it. We must add the proviso: Psst! – except for those bumps that we are properly ignoring. Else we will conclude, absurdly, that nothing is flat. (Simplify by ignoring departures from flatness that consist of gentle curvature.) We can restate the definition. Say that we presuppose proposition Q iff we ignore all possibilities in which not-Q. To close the circle: we ignore just those possibilities that falsify our presuppositions. Proper presupposition corresponds, of course, to proper ignoring. Then S knows thatP iffS’s evidence eliminates every possibility in which not- P – Psst! – except for those possibilities that conflict with our proper presuppositions? The rest of (modal) epistemology examines the sotto voce proviso. It asks: what may we properly presuppose in our ascriptions of knowledge? Which of all the uneliminated alternative possibilities may not properly be ignored? Which ones are the ‘relevant alter- natives’? – relevant, that is, to what the subject does and doesn’t knowT ° In reply, we can list several rules. 1~ We begin with three prohibitions: rules to tell us what possibili- ties we may not properly ignore. First, there is the Rule of Actuality. The possibility that actually obtains is never properly ignored; actuality is always a relevant alternative; nothing false may properly be presup- posed. It follows that only what is true is known, wherefore we did not have to include truth in our definition of knowledge. The rule is ‘externalist’ – the subject himself may not be able to tell what is properly ignored. In judging which of his ignorings are proper, hence what he knows, we judge his success in knowing – not how well he tried. When the Rule of Actuality tells us that actuality may never be properly ignored, we can ask: whose actuality? Ours, when we ascribe knowledge or ignorance to others? Or the subject’s? In simple cases, the question is silly. (In fact, it sounds like the sort of pernicious nonsense we would expect from someone who mixes up what is true with Peter Unger, Ignorance, chapter II. I discuss the case, and briefly foreshadow the present paper, in my ‘Scorekeeping in a Language Game’, Journal of Philosophical Logic 8 (1979) pp. 339- 359, esp. pp. 353-355. 9 See Robert Stalnaker, ‘Presuppositions’, Journal of Philosophical Logic 2 (1973) pp. 447-457; and ‘Pragmatic Presuppositions’ in Milton Munitz and Peter Unger (eds.), Semantics and Philosophy (New York: New York University Press, 1974). See also my ‘Scorekeeping in a Language Game’. The definition restated in terms of presupposition resembles the treatment of knowledge in Kenneth S. Ferguson, Philosophical Scepticism (Cornell University doctoral dissertation, 1980). lo See Fred Dretske, ‘Epistemic Operators’, The Journal of Philosophy 67 (1970) pp. 1007-1022, and ‘The Pragmatic Dimension of Knowledge’, Philosophical Studies 40 (1981) pp. 363-378; Alvin Goldman, ‘Discrimination and Perceptual Knowledge’, The Journal of Philosophy 73 (1976) pp. 771-791; G.C. Stine, ‘Skepticism, Relevant Alternatives, and Deductive Closure’, Philosophical Studies 29 (1976) pp. 249-261; and Stewart Cohen, ‘How to be A Fallibilist’, Philosophical Perspectives 2 (1988) pp. 91-123. H Some of them, but only some, taken from the authors just cited. Downloaded By: [Ingenta Content Distribution – Routledge] At: 09:32 20 January 2009554 Elusive Knowledge But, of course, I am not entitled to ignore just any possibility I please. Else true ascriptions of knowledge, whether to myself or to others, would be cheap indeed. I may properly ignore some uneliminated possibilities; I may not properly ignore others. Our definition of knowledge requires a sotto voce proviso. S knows that P iff S’s evidence eliminates every possibility in which not-P -Psst! -except for those possibilities that we are properly ignoring. Unger suggests an instructive paralle!.’ Just as P is known iff there are no nated possibilities of error, so likewise a surface is flat iff there are no bumps on it. We must add the proviso: Psst! -except for those bumps that we are properly ignoring. Else we will conclude, absurdly, that nothing is flat. (Simplify by ignoring departures from flatness that consist of gentle curvature.) We can restate the definition. Say that we presuppose proposition Q iff we ignore all possibilities in which not-Q. To close the circle: we ignore just those possibilities that falsify our presuppositions. Proper presupposition corresponds, of course, to proper ignoring. Then S knows that P iff S’ s evidence eliminates every possibility in which P -Psst! -except for those possibilities that conflict with our proper presuppositions! The rest of (modal) epistemology examines the sotto voce proviso. It asks: what may we properly presuppose in our ascriptions of knowledge? Which of all the uneliminated alternative possibilities may not properly be ignored? Which ones are the ‘relevant natives’? -relevant, that is, to what the subject does and doesn’t knoW?lO In reply, we can list several rules.” We begin with three prohibitions: rules to tell us what ties we may not properly ignore. First, there is the Rule of Actuality. The possibility that actually obtains is never properly ignored; actuality is always a relevant alternative; nothing false may properly be posed. It follows that only what is true is known, wherefore we did not have to include truth in our definition of knowledge. The rule is ‘externalist’ -the subject himself may not be able to tell what is properly ignored. In judging which of his ignorings are proper, hence what he knows, we judge his success in knowing -not how well he tried. When the Rule of Actuality tells us that actuality may never be properly ignored, we can ask: whose actuality? Ours, when we ascribe knowledge or ignorance to others? Or the subject’s? In simple cases, the question is silly. (In fact, it sounds like the sort of pernicious nonsense we would expect from someone who mixes up what is true with Peter Unger, Ignorance, chapter II. I discuss the case, and briefly foreshadow the present paper, in my ‘Scorekeeping in a Language Game’, Journal of Philosophical Logic 8 (1979) pp. 339-359, esp. pp. 353-355. See Robert Stalnaker, ‘Presuppositions’, Journal of Philosophical Logic 2 (1973) pp. 447-457; and ‘Pragmatic Presuppositions’ in Milton Munitz and Peter Unger (eds.), Semantics and Philosophy (New York: New York University Press, 1974). See also my ‘Scorekeeping in a Language Game’. The definition restated in terms of presupposition resembles the treatment of knowledge in Kenneth S. Ferguson, Philosophical Scepticism (Carnell University doctoral dissertation, 1980). 10 See Fred Dretske, ‘Epistemic Operators’, The Journal of Philosophy 67 (1970) pp. 1007-1022, and ‘The Pragmatic Dimension of Knowledge’, Philosophical Studies 40 (1981) pp. 363-378; Alvin Goldman, ‘Discrimination and Perceptual Knowledge’, The Journal of Philosophy 73 (1976) pp. 771-791; G.C. Stine, ‘Skepticism, Relevant Alternatives, and Deductive Closure’, Philosophical Studies 29 (1976) pp. 249-261; and Stewart Cohen, ‘How to be A Fallibilist’, Philosophical Perspectives 2 (1988) pp. 91-123. 11 Some of them, but only some, taken from the authors just cited.
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