Again, when you say, “I grant you that you can't know when A has pain, you can only conjecture it”, you don't see the difficulty which lies in the different uses of the words “conjecturing” and “knowing”. What sort of impossibility were you referring to when you said you couldn't know? Weren't you thinking to || of a case analogous to that when one couldn't know whether the other man had a gold tooth in his mouth because he had his mouth shut? Here what you didn't know, you could nevertheless imagine to know; it made sense to say that you saw that tooth although you didn't see it; or rather, it makes sense to say that you don't see his tooth and therefore it also makes sense to say that you do. When on the other hand, you granted me that a man can't know whether the other person has pain, you do not wish to say that as a matter of fact people didn't know, but that it made no sense to say they knew (and therefore no sense to say they don't know). If therefore in this case you use the term “conjecture” or “believe”, you don't use it as opposed to “know”. That is, you did not state that knowing was a goal which you could not reach, and that you have to be contented with conjecturing; rather, there is no goal in this game. Just as when one says “You can't count through the whole
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series of cardinal numbers”, one doesn't state a fact about human frailty but about a convention which we have made. Our statement is not comparable, though always falsely compared, with such a one as “it is impossible for a human being to swim across the Atlantic”; but it is analogous to a statement like “there is no goal in an endurance race”. And this is one of the things which the person feels dimly who is not satisfied with the explanation that though you can't know … you can conjecture ….