Now I think you may have noticed that when you make a statement to another person, and he answers "How do you know that that is so?" he very often means to suggest that you do _not_ know it. And yet, though he means to suggest that you do not _know_ it, he may not for a moment wish to suggest that you do not _believe_ it, nor even that you have not that degree or kind of conviction, which goes beyond mere belief, and which may be taken to be essential to anything which can properly be called knowledge. He does not mean to suggest for a moment that you are saying something which you do not believe to be true, or even that you are not thoroughly convinced of its truth. What he does mean to suggest is that what you asserted was not _true_, even though you may not only have believed it but felt sure that it was true. He suggests that you don't _know_ it, in the sense that what you believe or feel sure of is not true. Now I point this out, not because I myself mean to suggest that we don't know the existence of other persons, but merely in order to show that the word "know" is sometimes used in a sense in which it is not merely equivalent to "believe" or "feel sure of." When the question "How do you _know_ that?" is asked, the questioner does not merely mean to ask "how do you come to believe that, or to be convinced of it?" He sometimes, and I think generally, means to ask a question with regard to the _truth_, and not with regard to the _existence_ of your belief. And similarly when I ask the question "How do we know that other people exist?" I do _not_ mean to ask "How do we come to believe in or be convinced of their existence?" I do not intend to discuss this question _at all._ I shall not ask what _suggests_ to us our belief in the existence of other persons or of an external world; I shall not ask whether we arrive at it by inference or by "instinct" or in any other manner, which ever has been or may be suggested: I shall discuss no question of any kind whatever with regard to its origin, or cause, or the way in which it arises. These psychological questions are _not_ what I propose to discuss. When I ask the question "How do we know that other people exist?" I do _not_ mean: "How does our belief in their existence arise?" But if I do not mean this what do I mean P I have said that I mean to ask a question with regard to the _truth_ of that belief; and the particular question which I mean to ask might be expressed in the words: _What reason have_ we for our belief in the existence of other persons? But these are words which themselves need some explanation, and I will try to give it.