It seems to me certain that the perception of foreign bodies of a certain sort, although a necessary, is not the only, part of the basis of our belief in other persons. The greatest disagreement with this view that I know of has been expressed by Professor Aaron in a paper published in Philosophy, XIX, 72. He claims that, since one does not really know “what it means to be a mind in one's own case,” the question whether we can be certain that there are other minds is meaningless except as reducible to the question whether such propositions as “Robinson exists” are propositions which we can be certain about. And he tries to show that no more is involved in the analysis of “Robinson exists” than would be involved in the analysis of propositions of whose truth we can be perceptually certain, such as “That table over there exists” or “The Eiffel Tower exists.” My assurance that Robinson exists is not the assurance that something called Robinson's mind exists. It is the perfectly ordinary perceptual assurance that ‘the person over there’ exists. “You ask me how I am certain that Robinson exists and I answer, ‘Well, look, there he is.’ It would be absurd for anyone to say that he does not exist when I see him here before me and hear him talk and watch him move that chair.”