When I said that if we moved our hand upward a little, we touch our eye, I was referring to tactile evidence only. That is, the criterion for my finger touching my eye was to be only that I had the particular feeling which would have made me say that I was touching my eye, even if I had no visual evidence for it, and even if, on looking into a mirror, I saw my finger not touching my eye but, say, my forehead. Just as the “little distance” I referred to was a tactile or kinaesthetic one, so also the places of which I said, “they
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lie a little distance apart” were tactile places. To say that my finger in tactile and kinaesthetic space moves from my tooth to my eye then means that I have those tactile and kinaesthetic experiences w[g|h]ich we normally have when we say “my finger moves from my tooth to my eye”. But what we regard as evidence for this latter proposition is, as we all know, by no means only tactile and kinaesthetic. In fact if I had the tactile and kinaesthetic sensations referred to, I might still deny the proposition “my finger moves … etc. …” because of what I saw. That proposition is a proposition about physical objects. (And now don't think that the expression “physical objects” is meant to distinguish one kind of physical object from another.) The grammar of propositions which we call propositions about physical objects admits of a variety of evi[s|d]ences for every such proposition. It characterises the grammar of the proposition “my finger moves etc.” that I regard the propositions “I see it move”, “I feel it move”, “He sees it move”, “He tells me that it moves”, etc. as evidence for it. Now if I say “I see my hand move”, this at first sight seems to presuppose that I agree with the proposition “my hand moves”. But if I regard the proposition “I see my hand move” as one of the evidences for the proposition “my hand moves”, the truth of the latter is, of course, not presupposed in the truth of the former. One might therefore suggest the expression “It looks as though my hand were moving” instead of “I see my hand moving”. But this express-
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ion, although it indicates that my hand may appear to be moving without really moving, might still suggest that after all there must be a hand in order that it should appear to be moving; whereas we could easily imagine cases in which the proposition describing the visual evidence is true and at the same time other evidences make us say that I have no hand. Our ordinary way of expression obscures this. We are handicapped in ordinary language by having to describe, say, a tactile sensation by means of terms for physical objects such as the word “eye”, “finger”, etc. when ˇwhat we want to say does not entail the existence of an eye or finger etc.: We have to use a roundabout description of our sensations. This of course does not mean that our ordinary language is insufficient for our purposes, but that it is slightly cumbrous and sometimes misleading. The reason for this peculiarity of our language is of course the regular coincidence of certain sense experiences. Thus when I feel my arm moving I mostly also can see it moving. And if I touch it with my hand, also that hand feels the motion, etc.. (The man whose foot has been amputated will describe a particular pain as pain in his foot.) We [g|f]eel in such cases a strong need for such an expression as: “a sensation travels from my tactual cheek to my tactual eye”. I said all this because, if you are aware of the tactual and kinaesthetic environment of a pain, you may find a difficulty in imagining that one could have toothache anywhere else than in one's own teeth. But if we
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imagine such a case, this simply means that we imagine a correlation between visual, tactual, kinaesthetic, etc., experiences different from the ordinary correlation. Thus we can imagine a person having the sensation of toothache plus those tactual and kinaesthetic experiences which are normally bound up with seeing his hand travelling from his tooth to his nose, to his eyes, etc., but correlated to the visual experience of his hand moving to those places in another person's face. Or again, we can imagine a person having the kinaesthetic sensation of moving his hand, and the tactual sensation, in his fingers and face, of his fingers moving over his face, whereas his kinaesthetic and visual sensations should have to be described as those of his fingers moving over his knee. If we had a sensation of toothache plus certain tactual and kinaesthetic sensations usually characteristic of touching the painful tooth and neighbouring parts of our face, and if these sensations were accompanied by seeing my hand touch, and move about on, the edge of my table, we should feel doubtful whether to call this experience an experience of toothache in the table or not. If, on the other hand, the tactual and kinaesthetic sensations described were correlated to the visual experience of seeing my hand touch a tooth and other parts of the face of another person, there is no doubt that I would call this experience “toothache in another person's tooth.”