Wittgenstein:
On Certainty1. If you do 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 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 shows 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 "2x2=4" nonsense in the same way, and not a proposition of arithmetic, apart from particular occasions? "2x2=4" is a true proposition of arithmetic - not "on particular occasions" nor "always" - but the spoken or written sentence "2x2=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 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 from the utterance together with its 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 remains to be shown.
15. It needs to be shown 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 must admit of being 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.
21. Moore's view really comes down to this: the concept 'know' is analogous to the concepts 'believe', 'surmise', 'doubt', 'be convinced' in that the statement "I know..." can't be a mistake. And if that is so, then there can be an inference from such an utterance to the truth of an assertion. And here the form "I thought I knew" is being overlooked. - But if this latter is inadmissible, then a mistake in the assertion must be logically impossible too. And anyone who is acquainted with the language-game must realize this - an assurance from a reliable man that he knows cannot contribute anything.
22. It would surely be remarkable if we had to believe the reliable person who says "I can't be wrong"; or who says "I am not wrong".
23. If I don't know whether someone has two hands (say, whether they have been amputated or not) I shall believe his assurance that he has two hands, if he is trustworthy. And if he says he knows it, that can only signify to me that he has been able to make sure, and hence that his arms are e.g. not still concealed by coverings and bandages, etc.etc. My believing the trustworthy man stems from my admitting that it is possible for him to make sure. But someone who says that perhaps there are no physical objects makes no such admission.
24. The idealist's question would be something like: "What right have I not to doubt the existence of my hands?" (And to that the answer can't be: I know that they exist.) But someone who asks such a question is overlooking the fact that a doubt about existence only works in a language-game. Hence, that we should first have to ask: what would such a doubt be like?, and don't understand this straight off.
25. One may be wrong even about "there being a hand here". Only in particular circumstances is it impossible. - "Even in a calculation one can be wrong - only in certain circumstances one can't."
26. But can it be seen from a rule what circumstances logically exclude a mistake in the employment of rules of calculation?
What use is a rule to us here? Mightn't we (in turn) go wrong in applying it?
27. If, however, one wanted to give something like a rule here, then it would contain the expression "in normal circumstances". And we recognize normal circumstances but cannot precisely describe them. At most, we can describe a range of abnormal ones.
28. What is 'learning a rule'? - This.
What is 'making a mistake in applying it'? - This. And what is pointed to here is something indeterminate.
29. Practice in the use of the rule also shows what is a mistake in its employment.
30. When someone has made sure of something, he says: "Yes, the calculation is right", but he did not infer that from his condition of certainty. One does not infer how things are from one's own certainty.
Certainty is as it were a tone of voice in which one declares how things are, but one does not infer from the tone of voice that one is justified.
31. The propositions which one comes back to again and again as if bewitched - these I should like to expunge from philosophical language.
32. It's not a matter of Moore's knowing that there's a hand there, but rather we should not understand him if he were to say "Of course I may be wrong about this." We should ask "What is it like to make such a mistake as that?" - e.g. what's it like to discover that it was a mistake?
33. Thus we expunge the sentences that don't get us any further.
34. If someone is taught to calculate, is he also taught that he can rely on a calculation of his teacher's? But these explanations must after all sometime come to an end. Will he also be taught that he can trust his senses - since he is indeed told in many cases that in such and such a special case you cannot trust them? -
Rule and exception.
35. But can't it be imagined that there should be no physical objects? I don't know. And yet "There are physical objects" is nonsense. Is it supposed to be an empirical proposition? -
And is this an empirical proposition: "There seem to be physical objects"?
36. "A is a physical object" is a piece of instruction which we give only to someone who doesn't yet understand either what "A" means, or what "physical object" means. Thus it is instruction about the use of words, and "physical object" is a logical concept. (Like colour, quantity,...) And that is why no such proposition as: "There are physical objects" can be formulated.
Yet we encounter such unsuccessful shots at every turn.
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83. The truth of certain empirical propositions belongs to our frame of reference.
84. Moore says he knows that the earth existed long before his birth. And put like that it seems to be a personal statement about him, even if it is in addition a statement about the physical world. Now it is philosophically uninteresting whether Moore knows this or that, but it is interesting that, and how, it can be known. If Moore had informed us that he knew the distance separating certain stars, we might conclude from that that he had made some special investigations, and we shall want to know what these were. But Moore chooses precisely a case in which we all seem to know the same as he, and without being able to say how. I believe e.g. that I know as much about this matter (the existence of the earth) as Moore does, and if he knows that it is as he says, then I know it too. For it isn't, either, as if he had arrived at this proposition by pursuing some line of thought which, while it is open to me, I have not in fact pursued.
85. And what goes into someone's knowing this? Knowledge of history, say? He must know what it means to say: the earth has already existed for such and such a length of time. For not any intelligent adult must know that. We see men building and demolishing houses, and are led to ask:"How long has this house been here?" But how does one come on the idea of asking this about a mountain, for example? And have all men the notion of the earth as a body, which may come into being and pass away? Why shouldn't I think of the earth as flat, but extending without end in every direction (including depth)? But in that case one might still say "I know that this mountain existed long before my birth." - But suppose I met a man who didn't believe that?
86. Suppose I replaced Moore's "I know" by "I am of the unshakeable conviction"?
87. Can't an assertoric sentence, which was capable of functioning as an hypothesis, also be used as a foundation for research and action? I.e. can't it simply be isolated from doubt, though not according to any explicit rule? It simply gets assumed as a truism, never called in question, perhaps not even ever formulated.
88. It may be for example that all enquiry on our part is set so as to exempt certain propositions from doubt, if they were ever formulated. They lie apart from the route travelled by enquiry.
89. One would like to say: "Everything speaks for, and nothing against the earth's having existed long before..."
Yet might I not believe the contrary after all? But the question is: What would the practical effects of this belief be? - Perhaps someone says: "That's not the point. A belief is what it is whether it has any practical effects or not." One thinks: It is the same adjustment of the human mind anyway.
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118. Now would it be correct to say: So far no one has opened my skull in order to see whether there is a brain inside; but everything speaks for, and nothing against, its being what they would find there?
119. But can it also be said: Everything speaks for, and nothing against the table's still being there when no one sees it? For what does speak for it?
120. But if anyone were to doubt it, how would his doubt come out in practice? And couldn't we peacefully leave him to doubt it, since it makes no difference at all?
121. Can one say: "Where there is no doubt there is no knowledge either"?
122. Doesn't one need grounds for doubt?
123. Wherever I look, I find no ground for doubting that...
124. I want to say: We use judgments as principles of judgment.
125. If a blind man were to ask me "Have you got two hands?" I should not make sure by looking. If I were to have any doubt of it, then I don't know why I should trust my eyes. For why shouldn't I test my eyes by looking to find out whether I see my two hands? What is to be tested by what? (Who decides what stands fast?)
And what does it mean to say that such and such stands fast?
126. I am not more certain of the meaning of my words that I am of certain judgments. Can I doubt that this colour is called "blue"?
(My) doubts form a system.
127. For how do I know that someone is in doubt? How do I know that he uses the words "I doubt it" as I do?
128. From a child up I learnt to judge like this. This is judging.
129. This is how I learned to judge; this I got to know as judgment.
130. But isn't it experience that teaches us to judge like this, that is to say, that it is correct to judge like this? But how does experience teach us, then? We may derive it from experience, but experience does not direct us to derive anything from experience. If it is the ground for our judging like this, and not just the cause, still we do not have a ground for seeing this in turn as a ground.
131. No, experience is not the ground for our game of judging. Nor is its outstanding success.
132. Men have judged that a king can make rain; we say this contradicts all experience. Today they judge that aeroplanes and the radio etc. are means for the closer contact of peoples and the spread of culture.
133. Under ordinary circumstances I do not satisfy myself that I have two hands by seeing how it looks. Why not? Has experience shown it to be unnecessary? Or (again): Have we in some way learnt a universal law of induction, and do we trust it here too? - But why should we have learnt one universal law first, and not the special one straight away?
134. After putting a book in a drawer, I assume it is there, unless... "Experience always proves me right. There is no well attested case of a book's (simply) disappearing." It has often happened that a book has never turned up again, although we thought we knew for certain where it was. - But experience does really teach that a book, say, does not vanish away. (E.g. gradually evaporates.) But is it this experience with books etc. that leads us to assume that such a book has not vanished away? Well, suppose we were to find that under particular novel circumstances books did vanish away. - Shouldn't we alter our assumption? Can one give the lie to the effect of experience on our system of assumption?
135. But do we not simply follow the principle that what has always happened will happen again (or something like it)? What does it mean to follow this principle? Do we really introduce it into our reasoning? Or is it merely the natural law which our inferring apparently follows? This latter it may be. It is not an item in our considerations.
136. When Moore says he knows such and such, he is really enumerating a lot of empirical propositions which we affirm without special testing; propositions, that is, which have a peculiar logical role in the system of our empirical propositions.
137. Even if the most trustworthy of men assures me that he knows things are thus and so, this by itself cannot satisfy me that he does know. Only that he believes he knows. That is why Moore's assurance that he knows... does not interest us. The propositions, however, which Moore retails as examples of such known truths are indeed interesting. Not because anyone knows their truth, or believes he knows them, but because they all have a similar role in the system of our empirical judgments.
138. We don't, for example, arrive at any of them as a result of investigation.
There are e.g. historical investigations and investigations into the shape and also the age of the earth, but not into whether the earth has existed during the last hundred years. Of course many of us have information about this period from our parents and grandparents; but maynt' they be wrong? - "Nonsense!" one will say. "How should all these people be wrong?" - But is that an argument? Is it not simply the rejection of an idea? And perhaps the determination of a concept? For if I speak of a possible mistake here, this changes the role of "mistake" and "truth" in our lives.
139. Not only rules, but also examples are needed for establishing a practice. Our rules leave loop-holes open, and the practice has to speak for itself.
140. We do not learn the practice of making empirical judgments by learning rules: we are taught judgments and their connexion with other judgments. A totality of judgments is made plausible to us.
141. When we first begin to believe anything, what we believe is not a single proposition, it is a whole system of propositions. (Light dawns gradually over the whole.)
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287. The squirrel does not infer by induction that it is going to need stores next winter as well. And no more do we need a law of induction to justify our actions or our predictions.
288. I know, not just that the earth existed long before my birth, but also that it is a large body, that this has been established, that I and the rest of mankind have forebears, that there are books about all this, that such books don't lie, etc. etc. etc. And I know all this? I believe it. This body of knowledge has been handed on to me and I have no grounds for doubting it, but, on the contrary, all sorts of confirmation.
And why shouldn't I say that I know all this? Isn't that what one does say?
But not only I know, or believe, all that, but the others do too. Or rather, I believe that they believe it.
289. I am firmly convinced that others believe, believe they know, that all that is in fact so.
290. I myself wrote in my book that children learn to understand a word in such and such a way. Do I know that, or do I believe it? Why in such a case do I write not "I believe etc." but simply the indicative sentence?
291. We know that the earth is round. We have definitively ascertained that it is round.
We shall stick to this opinion, unless our whole way of seeing nature changes. "How do you know that?" - I believe it.
292. Further experiments cannot give the lie to our earlier ones, at most they may change our whole way of looking at things.
293. Similarly with the sentence "water boils at 100 C".
294. This is how we acquire conviction, this is called "being rightly convinced".
295. So hasn't one, in this sense, a proof of the proposition? But that the same thing has happened again is not a proof of it; though we do say that it gives us a right to assume it.
296. This is what we call an "empirical foundation" for our assumptions.
297. For we learn, not just that such and such experiments had those and those results, but also the conclusion which is drawn. And of course there is nothing wrong in our doing so. For this inferred proposition is an instrument for a definitive use.
298. 'We are quite sure of it' does not mean just that every single person is certain of it, but that we belong to a community which is bound together by science and education.
299. We are satisfied that the earth is round. [In English]
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