1. If you do know that here is one hand,1 we’ll grant you all the rest. When one says that such and such a proposition can’t be proved, of course that does not mean that it can’t be derived from other propositions; any proposition can be derived from other ones. But they may be no more certain than it is itself. (On this a curious remark by H. Newman.)
2. From its seeming to me—or to everyone— to be so, it doesn’t follow that it is so. What we can ask is whether it can make sense to doubt it.
3. If e.g. someone says “I don’ t know if there’s a hand here” he might be told “Look closer”.—This possibility of satisfying oneself is part of the language-game. Is one of its essential features.
4. “I know that I am a human being.” In order to see how unclear the sense of this proposition is, consider its negation. At most it might be taken to mean “I know I have the organs of a human”. (E.g. a brain which, after all, no one has ever yet seen.) But what about such a proposition as “I know I have a brain”? Can I doubt it? Grounds for doubt are lacking! Everything speaks in its favour, nothing against it. Nevertheless it is imaginable that my skull should turn out empty when it was operated on.
5. Whether a proposition can turn out false after all depends on what I make count as determinants for that proposition.
6. Now, can one enumerate what one knows (like Moore)? Straight off like that, I believe not.—For otherwise the expression “I know” gets misused. And through this misuse a queer and extremely important mental state seems to be revealed.
7. My life shews that I know or am certain that there is a chair over there, or a door, and so on.—I tell a friend e.g.“Take that chair over there”, “Shut the door”, etc. etc.
8. The difference between the concept of ‘knowing’ and the concept of ‘being certain’ isn’t of any great importance at all, except where “I know” is meant to mean: I can’t be wrong. In a law-court, for example, “I am certain” could replace “I know” in every piece of testimony. We might even imagine its being forbidden to say “I know” there. [A passage in Wilhelm Meister, where “You know” or “You knew” is used in the sense “You were certain”, the facts being different from what he knew.]
9. Now do I, in the course of my life, make sure I know that here is a hand—my own hand, that is?
10. I know that a sick man is lying here? Nonsense! I am sitting at his bedside, I am looking attentively into his face.—So I don’t know, then, that there is a sick man lying here? Neither the question nor the assertion makes sense. Any more than the assertion “I am here”, which I might yet use at any moment, if suitable occasion presented itself.—Then is “2_2_4” nonsense in the same way, and not a proposition of arithmetic, apart from particular occasions? “2_2_4” is a true proposition of arithmetic—not “on particular occasions” nor “always”—but the spoken or written sentence “2_2_4” in Chinese might have a different meaning or be out and out nonsense, and from this is seen that it is only in use that the proposition has its sense. And “I know that there’s a sick man lying here”, used in an unsuitable situation, seems not to be nonsense but rather seems matter-of-course, only because one can fairly easily imagine a situation to fit it, and one thinks that the words “I know that . . .” are always in place where there is no doubt, and hence even where the expression of doubt would be unintelligible.
69. I should like to say: “If I am wrong about this, I have no guarantee that anything I say is true.” But others won’t say that about me, nor will I say it about other people.
70. For months I have lived at address A, I have read the name of the street and the number of the house countless times, have received countless letters here and given countless people the address. If I am wrong about it, the mistake is hardly less than if I were (wrongly) to believe I was writing Chinese and not German.
71. If my friend were to imagine one day that he had been living for a long time past in such and such a place, etc. etc., I should not call this a mistake, but rather a mental disturbance, perhaps a transient one.
72. Not every false belief of this sort is a mistake.
73. But what is the difference between mistake and mental disturbance?
Or what is the difference between my treating it as a mistake and my treating it as mental disturbance?
74. Can we say: a mistake doesn’t only have a cause, it also has a ground? I.e., roughly: when someone makes a mistake, this can be fitted into what he knows aright.
75. Would this be correct: If I merely believed wrongly that there is a table here in front of me, this might still be a mistake; but if I believe wrongly that I have seen this table, or one like it, every day for several months past, and have regularly used it, that isn’t a mistake?
76. Naturally, my aim must be to give the statements that one would like to make here, but cannot make significantly.
77. Perhaps I shall do a multiplication twice to make sure, or perhaps get someone else to work it over. But shall I work it over again twenty times, or get twenty people to go over it? And is that some sort of negligence? Would the certainty really be greater for being checked twenty times?
78. And can I give a reason why it isn’t?
From: Wittgenstein, L. (1969). On Certainty, Oxford: Basil
Blackwell (Extract various paragraphs)
1 See G. E. Moore, “Proof of an External World”, Proceedings of the British Academy, Vol. XXV, 1939; also “A Defence of Common Sense” in Contemporary British Philosophy, 2nd Series, Ed.