The Paradox of Moore's Proof of an External World
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The Philosophical Quarterly doi: ./j.-...x THE PARADOX OF MOORE’S PROOF OF AN EXTERNAL WORLD B A C Moore’s proof of an external world is a piece of reasoning whose premises, in context, are true and warranted and whose conclusion is perfectly acceptable, and yet immediately seems flawed. I argue that neither Wright’s nor Pryor’s readings of the proof can explain this paradox. Rather, one must take the proof as responding to a sceptical challenge to our right to claim to have warrant for our ordinary empirical beliefs, either for any particular empirical belief we might have, or for belief in the existence of an external world itself. I show how Wright’s and Pryor’s positions are of interest when taken in connection with Humean scepticism, but that it is only linking it with Cartesian scepticism which can explain why the proof strikes us as an obvious failure. ... I remember with particular vividness that on one such occasion I found him poring over a piece of paper on which was handwritten a very short argument entitled ‘Proof of an External World’. I read it with some dismay. ‘Moore,’ I said, ‘surely your proof is a simple petitio principii?’ ‘Indeed, it is not,’ he smilingly replied. ‘Ah, so then does it perhaps suffer a failure of warrant transmission?’ ‘No’, he said. Bewildered, I ventured, ‘Then is it merely dialectically ineffec- tive?’ ‘No’, he said, smiling more mysteriously than ever. Then it came to me. ‘Moore’, I said, ‘is your proof merely completely irrelevant to the point at issue?’ ‘Yes!’ he said, clapping his hands with delight. From that point, we became firm friends. (With apologies to Jonathan Miller) I. THE PARADOX Normally, a philosophical paradox is a piece of reasoning which, starting from seemingly correct premises, leads us by seemingly unexceptionable means to an unbelievable conclusion. I propose to draw attention to an al- together different kind of paradoxical argument, one which employs only obviously valid forms of reasoning, starts from undisputed premises which, in context, are justified (or even known), leads to a perfectly acceptable conclusion, yet is still such that it seems evidently flawed. This, I submit, is the case with Moore’s claim to prove the existence of an external world: © The Author Journal compilation © The Editors of The Philosophical Quarterly Published by Blackwell Publishing, Garsington Road, Oxford , UK, and Main Street, Malden, , USA ANNALISA COLIVA THE PARADOX OF MOORE’S PROOF I can prove now, for instance, that two human hands exist. How? By holding up my depends, in Wright’s view, on his already having a warrant for the conclu- two hands, and saying, as I make a certain gesture with the right hand, ‘Here is one sion, since it is only in the context of such anterior information that he can hand’, and adding, as I make a certain gesture with the left, ‘and here is another’. And justifiably take his sense experience as a warrant for ‘Here is a hand’. The if, by doing this, I have proved ipso facto the existence of external things’ [of which proof, accordingly, is valid and proceeds from premises which there is no Moore takes his hands to be examples], ‘you will all see that I can also do it now in (non-sceptical) reason to deny are known, but it fails to be rationally per- numbers of other ways: there is no need to multiply examples.1 suasive: it cannot produce a first warrant for believing its conclusion. This proof is now standardly rendered as follows: James Pryor has contested Wright’s diagnosis.4 He agrees that doubts . Here is a hand about whether there is an external world would defeat the warrant supplied . If there is a hand here, then there is an external world by perceptual experience for the belief that here is a hand. But he thinks one . Therefore there is an external world. can certainly have a defeasible perceptual warrant for the premise that here is a hand, namely, seeming to see one’s hand, without needing any prior and This is an obviously valid inference. The first premise is quite clearly true, independent warrant for the conclusion that there is an external world – and indeed, we are willing to grant, known, in the kind of context in which indeed, without needing any collateral information at all, provided one does the proof is meant to be produced (one in which the thinker draws attention not already have any such doubts. Hence the proof, in his view, is not to his hand in front of his face). The second premise is a conceptual necess- epistemically circular. But, he suggests, it is dialectically ineffective: specifically, ity, knowable a priori (leaving idealist worries aside). The conclusion validly it fails in the anti-sceptical setting in which it is presented, since a sceptic will follows, and is absolutely acceptable and unparadoxical in any case. And yet already doubt its conclusion, that is, according to Pryor, will believe this it remains the case that Moore’s proof strikes (almost all of) us as an obviously (more probably) false, and hence will properly refuse to regard one’s current annoying failure, and does so immediately, on first encounter. The question is, experience as a warrant for the premise that here is a hand. But then since why? What can be wrong? by the sceptic’s lights there is no warrant for ‘Here is a hand’ in the first ff Various diagnoses have recently been o ered. According to Crispin place, there is no warrant to be transmitted from the premises to the conclu- Wright, for example, the proof fails because it is, in a certain way, epistem- sion of the argument, which will therefore fail to establish the conclusion ically circular.2 Wright does not question the first premise ‘Here is a hand’, that there is an external world, at least to the sceptic’s satisfaction. but argues that perceptual experience can provide a warrant for this premise Each of these positions, though instructive, is open to objection. But for only in a conducive informational setting which includes the thesis that there my purposes their most salient feature is that they take us into complex and is an external material world broadly manifest in ordinary sense experience. controversial issues concerning the rational architecture of our most basic ff A di erent example may make this clearer: seeming to see water falling perceptual warrants – issues on which many may well have no settled view. outside my window provides warrant for the belief that it is raining now So neither diagnosis can easily explain the more or less universal reaction of only in a setting where other sources of falling water, such as a hosepipe, are intellectual dismay on first encountering Moore’s proof. Wright’s account is excluded.3 Only in this kind of setting does the content of my current in difficulty on this point simply because it is not obvious or generally experience count as information that my belief that it is raining now is true. accepted that the underlying rational architecture of the proof is what he Hence, in the context of the proof, Wright would say that Moore’s per- thinks it is.5 Moreover, how on his proposed account are we to explain the ceptual experience of seeming to see a hand provides a warrant for the immediacy of our disappointment? After all, it is certainly not immediately premise that there is indeed a hand here only in an informational setting evident that the proof has the epistemic structure Wright thinks it has. His where it is assumed that there is an external world broadly manifest in sense account can predict our reaction only on the assumption that we are in experience. Thus Moore’s warrant for the premise that here is a hand 4 J. Pryor, ‘The Sceptic and the Dogmatist’, Noûs, (), pp. –; ‘What’s Wrong 1 G.E. Moore, ‘Proof of an External World’, repr. in his Philosophical Papers (London: With Moore’s Argument?’, Philosophical Issues, (), pp. –. George Allen & Unwin, ), pp. –, at p. 5 See, for instance, beside Pryor, also H. Beebee, ‘Transfer of Warrant, Begging the 2 C.J.G. Wright, ‘Facts and Certainty’, Proceedings of the British Academy, (), pp. Question and Semantic Externalism’, The Philosophical Quarterly, (), pp. –; –; ‘(Anti-)Sceptics Simple and Subtle: G.E. Moore and John McDowell’, Philosophy and M. Davies, ‘Epistemic Entitlement, Warrant Transmission and Easy Knowledge’, Proceedings of Phenomenological Research, (), pp. –. the Aristotelian Society, Supp. Vol. (), pp. –; C. Peacocke, The Realm of Reason (Oxford 3 I would like to thank an anonymous referee for this enlightening example. UP, ). © The Author Journal compilation © The Editors of The Philosophical Quarterly © The Author Journal compilation © The Editors of The Philosophical Quarterly ANNALISA COLIVA THE PARADOX OF MOORE’S PROOF some sense aware of that structure, and that our awareness functions as a who thinks that we cannot claim warrant for that belief, since the rational reason for our reaction. Pryor’s interpretation, for its part, has difficulty in stance towards it is one of agnosticism. But if one had indeed no view about explaining the near universality of the reaction. For Pryor’s account seems the existence of an external world, then if Pryor’s reconstruction of the proof to predict that the proof should seem perfectly all right to the general were correct, one could very simply acquire warrant to believe in it. For his reader, and that only an already committed sceptic, one who already doubts account predicts that if one has no view about the existence of an external the conclusion, should find it deficient.6 But surely one need not be a com- world and has an experience as of a hand in front of one, this experience mitted sceptic (who is, after all?), nor indeed have any doubt whatsoever will give one immediate warrant to believe that there is indeed a hand about its conclusion, in order to find Moore’s proof unsatisfactory.7 The where one seems to see it.