On Certainty (Über Gewissheit)
by Ludwig Wittgenstein
Edited by G. E. M. Anscombe and G. H. von Wright
Translated by Denis Paul and G. E. M. Anscombe
Basil Blackwell, Oxford, 1969, 1972
What we publish here belongs to the last year and a half of Wittgenstein’s life. In the middle of 1949 he visited the United States at the invitation of Norman Malcolm, staying at Malcolm’s house in Ithaca. Malcolm acted as a goad to his interest in Moore’s ‘defence of common sense’, that is to say his claim to know a number of propositions for sure, such as “Here is one hand, and here is another”, and “The earth existed for a long time before my birth”, and “I have never been far from the earth’s surface”. The first of these comes in Moore’s ‘Proof of the External World’. The two others are in his ‘Defence of Common Sense’; Wittgenstein had long been interested in these and had said to Moore that this was his best article. Moore had agreed. This book contains the whole of what Wittgenstein wrote on this topic from that time until his death. It is all first-draft material, which he did not live to excerpt and polish.
The material falls into four parts; we have shown the divisions at #65, #192, #299. What we believe to be the first part was written on twenty loose sheets of lined foolscap, undated. These Wittgenstein left in his room in G. E. M. Anscombe’s house in Oxford, where he lived (apart from a visit to Norway in the autumn) from April 1950 to February 1951. I (G. E. M. A.) am under the impression that he had written them in Vienna, where he stayed from the previous Christmas until March; but I cannot now recall the basis of this impression. The rest is in small notebooks, containing dates; towards the end, indeed, the date of writing is always given. The last entry is two days before his death on April 29th 1951. We have left the dates exactly as they appear in the manuscripts. The numbering of the single sections, however, is by the Editors.
It seemed appropriate to publish this work by itself. It is not a selection; Wittgenstein marked it off in his notebooks as a separate topic, which he apparently took up at four separate periods during this eighteen months. It constitutes a single sustained treatment of the topic.
G. E. M. Anscombe G. H. von Wright
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1. If you know that here is one hand, 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 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 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 to 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 x 2 = 4” nonsense in the same way, and not a proposition of arithmetic, apart from particular occasions? “2 x 2 = 4” is a true proposition of arithmetic—not “on particular occasions” nor “always”—but the spoken or written sentence “2 x 2 = 4” in Chinese might have a different meaning or be out and out nonsense. 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.
11. We just do not see how very specialized the use of “I know” is.
12. —For “I know” seems to describe a state of affairs which guarantees what is known, guarantees it as a fact. One always forgets the expression “I thought I knew”.
13. For it is not as though the proposition “It is so” could be inferred from someone else’s utterance: “I know it is so”. Nor with the utterance together with it not being a lie.—But can’t I infer “It is so” from my own utterance “I know etc.”? Yes; and also “There is a hand there” follows from the proposition “He knows that there’s a hand there”. But from his utterance “I know…” it does not follow that he does know it.
14. That he does know takes some shewing.
15. It needs to be shewn that no mistake was possible. Giving the assurance “I know” doesn’t suffice. For it is after all only an assurance that I can’t be making a mistake, and it needs to be objectively established that I am not making a mistake about that.
16. “If I know something, then I also know that I know it, etc.” amounts to: “I know that” means “I am incapable of being wrong about that”. But whether I am so needs to be established objectively.
17. Suppose now I say “I’m incapable of being wrong about this: that is a book” while I point to an object. What would a mistake here be like? And have I any clear idea of it?
18. “I know” often means: I have the proper grounds for my statement. So if the other person is acquainted with the language-game, he would admit that I know. The other, if he is acquainted with the language-game, must be able to imagine how one may know something of the kind.
19. The statement “I know that here is a hand” may then be continued: “for it’s my hand that I’m looking at.” Then a reasonable man will not doubt that I know.-Nor will the idealist; rather he will say that he was not dealing with the practical doubt which is being dismissed, but there is a further doubt behind that one.-That this is an illusion has to be shown in a different way.
20. “Doubting the existence of the external world” does not mean for example doubting the existence of a planet, which later observations proved to exist.-Or does Moore want to say that knowing that here is his hand is different in kind from knowing the existence of the planet Saturn? Otherwise it would be possible to point out the discovery of the planet Saturn to the doubters and say that its existence has been proved, and hence the existence of the external world as well.
[*TO BE CONTINUED…*]
 See G.E. Moore, “Proof of an External World”, Proceedings of the British Academy, Vol. XXV, 1939; also “A Defense of Common Sense” in Contemporary British Philosophy, 2nd Series, Ed. J.H. Muirhead, 1925. Both papers are in Moore’s Philosophical Papers, London, George Allen and Unwin, 1959. Editors.