Another such trouble, closely akin, is expressed in the sentence: “I can only know that I have personal experiences, not that anyone else has”. ‒ ‒ ‒ Shall we then call it an unnecessary hypothesis that anyone else has personal experiences? ‒ ‒ ‒ But is it an hypothesis at all? For how can I even make the hypothesis if it transcends all possible experience? How could such a hypothesis be backed by meaning? (Is it not like paper money, not backed by gold?) ‒ ‒ ‒ It doesn't help if anyone tells us that, though we don't know whether the other person has pains, we certainly believe it when, for instance, we pity him. Certainly we shouldn't pity him if we didn't believe that he had pains; but is this a philosophical, a metaphysical, belief: Does a realist pity me more than an idealist or a solipsist? ‒ ‒ ‒ In fact the solipsist asks: “How can we believe that the other has pain; what does it mean to believe this? How can the expression of such a supposition make sense?” Now the answer of the common sense philosopher (which, N.B., is not the common sense man, who is as far from realism as from idealism) the answer of the common sense philosopher is that surely there is no difficulty in the idea of supposing, thinking, imagining, that someone else has what I have. But the trouble with the realist is always that he does not solve but skip the difficulties which his adversaries see, though they too don't succeed in solving them. The realist answer, for us, just brings out the difficulty; for who argues like this overlooks the difference between different usages of the words “to have”, “to imagine”. “A has a gold tooth” means that the tooth is in A's mouth. Now the case of his toothache, of which I say I am not able to feel it because it is in his mouth, is not analogous to the case of the gold tooth. It is the apparent analogy, and again the lack of analogy, between these cases which causes our trouble. And it is this troublesome feature in our grammar which the realist does not notice. It is conceivable that I feel pain in a tooth in another man's mouth; and the man who says that he cannot feel the other's toothache is not denying this. The grammatical difficulty which we are in we shall only see clearly if we get familiar with the idea of feeling pain in another person's body. For otherwise, in puzzling about this problem, we shall be liable to confuse our metaphysical proposition “I can't feel his pain” with the experiential proposition, “We can't have (haven't as a rule) pains in another person's tooth”. In this proposition the word “can't” is used in the same way as in the proposition “An iron nail can't scratch glass”. (We could write this in the form “experience teaches that an iron nail doesn't scratch glass”, thus doing away with the “can't”). In order to see that it is conceivable that one person should have pain in another person's body, one must examine what sort of facts we call criteria for a pain being in a certain place. It is easy to imagine the following case: When I see my hands I am not always aware of their connection with the rest of my body. That is to say, I often see my hand moving but don't see the arm which connects it to my torso. Nor do I necessarily, at the time, check up on the arm's existence in any other way. Therefore the hand may, for all I know, be connected to the body of a man standing beside me (or, of course, not to a human body at all). Suppose I feel a pain which in the evidence of the pain alone, e.g., with closed eyes, I should call a pain in my left hand. Someone asks me to touch the painful spot with my right hand. I do so and looking round perceive that I am touching my neighbour's hand (meaning the hand connected to my neighbour's torso.)