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G.E. Moore「Proof of an External World」#1 "here is a hand" argument [ 分析哲学 ] G.E. Moore is a 20th century English analytic philosopher. He makes interesting philosophical contributions in areas such as epistemology, ethics, and so forth. In this essay, I will especially focus on his paper, Proof of an External World (1939), which has received much attention among philosophers. As Moore’s title suggests, he offers a proof of the existence of external objects by taking into account our common sense. His proof is straightforward; he argues that we know the existence of external objects, just as we know the existence of our own hands. However, this proof seems to completely reject the philosophical sceptic’s argument that says that it is impossible to have knowledge of anything external, including even our own hands. Not only sceptics but everybody who is familiar with the problem of our knowledge of the external world immediately feels that Moore’s proof is clearly inadequate, and this leads them to think that it offers no solution to the sceptical refutation of the external world. But because the proof still has philosophical significance, we will look at Moore’s intention in the Proof. In brief, Moore intentionally ignores the sceptical argument and he adopts a position antithetical to scepticism. Moore argues that if something external can be known by our immediate perception (e.g. we of course know I have a hand), it will be much more reasonable to reject the sceptical conclusion than it will be to accept it. He insists that we do always have actual knowledge of the external world, which is diametrically opposed to the sceptical argument. That is to say that Moore’s proof successfully leads the anti-sceptical position to be equal to the sceptical position. However, Moore has been also criticised by some philosophers; for example, Barry Stroud argues that Moore should be more philosophical for being equal to criticism. And, finally, I will look at the relationship between Moore and naturalised epistemology. I believe that Moore’s anti-sceptical position and naturalism both have the same basis, namely that we can attain knowledge using empirical methods. Before moving on to the main discussion of Moore’s Proof, it is worth summarizing the sceptical argument, rooted in the thought of Descartes. Many philosophers have asked the question of whether we can have knowledge of the existence of the external world, but the sceptical argument has not conceded that such knowledge is possible. Descartes, in First Meditation, suggests that, “As if I did not recall having been deceived before by just such thoughts in sleep! When I think more carefully about this, I see so plainly that sleep and waking can never be distinguished by any certain signs, that I am bewildered; and this itself confirms the idea of my being asleep.” (Descartes, 1641). We cannot even know that we are either dreaming or awake, and our perception gives us no conclusive or certain knowledge about the external world. So our perceptual justification for our beliefs about the world outside our mind is not defensible. This negative philosophical conclusion became the basis of philosophical scepticism. I turn now to Moore’s famous and, as some say, notorious paper, Proof of an External World (hereafter, PEW). Moore’s proof of external objects can be seen in the following quotation: “By holding up my two hands, and saying, as I make a certain gesture with the right hand, ‘here is one hand,’ and adding, as I make a certain gesture with the left, and ‘here is another.’ And if, by doing this, I have proved ipso facto the existence of external things […].”(PEW) Moore believes this argument successfully proves the existence of objects. The proof goes as follows: P1. Here is one hand P2. Here is another ------------------------------------------------- C1. Therefore, two hands exist C2. Therefore, two external objects exist Moore shows what he considers to be “a perfectly rigorous proof” of the existence of things outside of us, and it is “probably impossible to give a better or more rigorous proof of anything.” (PEW) For him, the best way of proving the existence of something is to simply find it right before our eyes; he provides another example with the case of misprints on a page. The best way to prove whether the misprints exist is that we look and find that here is one misprint, and here is another, and here is another. Therefore we prove that there are three misprints on the page. That, Moore thinks, thoroughly proven. (Because this way of proof is in some favour at the middle of 20th century, the proof is assimilated and reconfigured by the ordinary language philosophers, such as Norman Malcolm and Alice Ambrose. But their interpretations were vigorously repudiated by Moore.) In addition, the proof surely satisfies, according to Moore, three logical conditionals: (1) the premise is distinct from the conclusion; (2) the person knows the premises to be true; and (3) the conclusion follows from the premises. It seems right that the proof meets the (1) and (3) conditionals because the premises of his proof above (here is a hand and here is another) are clearly distinct from the conclusion, and the conclusion follows the premises. Nevertheless, the most problematic point of his proof is on the (2) conditional, “the person knows the premise to be true,” which means the percipient knows he/she has two hands. Indeed the sceptic’s criticism focuses on this suggestion, but also this is the most significant point for understanding Moore’s intentions. We shall now look more carefully into this matter, because it is obvious that the premises lead to the first conclusion (C1) but it is not obvious that the first conclusion entails the second conclusion (C2). Landesman (1999) explains this logical gap between two conclusions. In brief, external objects, such as one’s own hand, a tree, and so on, are physical things that are perceivable and that exist independently of being perceived in contrast to such private objects as visual afterimages. Moore’s hands are paradigm cases of external physical objects. This means that from the fact that, for example, hands exist, it follows that there exist objects that are perceivable and independent and that count as external objects. If someone thought he saw a hand, but it turned out that what he saw did not exist independently of the perception of it, then it would follow that he did not actually see a hand but was undergoing a hallucination of the hand. --- ## 注 --- ## 参考文献

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