It is necessary, I think, to ask this question at this point, because there are some philosophers who hold that, in the case of some kinds of "content," at all events, to say that they "exist" is to say that they are "perceived." Some hold that to say "A exists" is to say neither more nor less than "A is perceived"--that the two expressions are perfect synonyms; and others again would say that by "A exists or is real" we may mean _more_ than that "A is perceived," but that we must at least mean this. Now, I have hitherto used the word "existence" pretty freely, and I think that, when I used it, I used it in its ordinary sense. I think it will generally have suggested to you precisely what I meant to convey, and I think that, in some cases at all events, it will not even have occurred to you to doubt whether you did understand what I meant by it. But, if these philosophers are right, then, if you _have_ understood what I meant by it, I have all along been using it in a sense, which renders the end of my last paragraph perfect nonsense. If these philosophers are right, then, when I assert that what _is_ perceived may yet _not_ exist, I am really asserting that what _is_ perceived may yet _not_ be perceived--I am contradicting myself. I am, of course, quite unaware that I am doing so. But these philosophers would say _either_ you are contradicting yourself, _or_ you are not using the word "exists" in its ordinary sense. And either of these alternatives would be fatal to my purpose. If I am not using the word in its ordinary sense, then I shall not be understood by anyone; and, if I am contradicting myself, then what I say will not be worth understanding.