On Certainty was written in response to G. E. Moore’s paper’s, Proof of an External World and A Defense of Common Sense in which Moore lists several propositions that he claims to know with certainty. Propositions such as the following: “Here is one hand” and “There exists at present a living human body, which is my body” – Moore continues to enumerate other propositions that he claims to know, with certainty, to be true. These propositions provide for Moore a proof of the external world, and as such, they supposedly form a buttress against the skeptic. However, as we shall see, it is not only Moore’s claim to knowledge that Wittgenstein criticizes, but he also criticizes the skeptic’s response to Moore, and their use of the word doubt.
Wittgenstein’s response to Moore is not entirely unsympathetic, although he argues that Moore’s propositions do not accomplish what Moore thinks they do, namely, to provide a proof of the external world; which in turn is supposed to undermine the doubts of the skeptic.
On Certainty begins with the following statement:
“If you do know that here is one hand, we’ll grant you all the rest (OC 1).”
So, Wittgenstein grants that if Moore knows what he claims to know, then Moore’s conclusion follows. Nevertheless, Wittgenstein argues throughout the book that Moore does not know what he thinks he knows. However, I think we are inclined to agree with Moore. After all, if we do not know this is a hand, then what do we know? It is this inclination to use the word know as Moore uses it that causes Wittgenstein’s response.
“Now, can one enumerate what one knows (like Moore)? Straight off like that, I believe not.-For otherwise the expression “I know” gets misused (OC 6).”
The disputes with Moore’s propositions are not only problematic, but they are also very subtle disputes, which means they are difficult to flesh out. One of the problems is that we sometimes fail to see the connection between the use of the word know, and the use of the word doubt, and the logic behind that use. It is the kind of logical link that is also seen between rule-following and making a mistake - one cannot happen without the other.
In the following quote from Wittgenstein we can see some slight differences in the use of the word know, and how it accomplishes the purpose of thwarting the misgivings of another.
“’I know what kind of tree that is.—It is a chestnut.’ ’I know what kind of tree that is.—I know it’s a chestnut.’ The first statement sounds more natural than the second. One will only say ‘I know’ a second time if one wants especially to emphasize certainty; perhaps to anticipate being contradicted. The first ‘I know’ means roughly: I can say.
“But in the other case one might begin with the observation ’that’s a …’, and then, when this is contradicted, counter by saying: ‘I know what sort of a tree it is’, and by this means lay emphasis on being sure (OC 591).”
One use of the word know is to alleviate doubt, or even to eliminate doubt as we participate in our everyday interactions. For instance, if I say that “I know that George is guilty,” then I am simply saying that I have the proper grounds for my knowledge. Hence, if you agree, you too will acknowledge that “I know that George is guilty.” If you acknowledge that I know what I claim to know, then presumably this lets the air out of the proverbial balloon of doubt; and if you disagree with my claim, then the doubt remains. So, if I make a claim to know what DNA is, and I have never studied biology, then it makes sense to have a question about my claim to knowledge. If on the other hand, you know that I have a PhD in biology from MIT, then it is very unlikely that you will doubt my claim to knowledge as it pertains to biology. Is not Moore trying to accomplish this very thing when he makes his claim to knowledge, that is, Moore is trying to negate the doubt of the skeptic by saying that he does have proof of the existence of his hands, which in turn leads to his conclusion that there is an external world. He is claiming to be in a position to know, and of course it is this assertion that Wittgenstein disputes.
Moore’s proof is supposed to show that the conclusion follows necessarily, and if it does, then the skeptic’s doubts are supposed to vanish. The proof would look something like the following:
- Moore has knowledge that he has two hands.
- Moore makes the inference from the fact that he has two hands, to the conclusion that there exists an external world.
- Hence, Moore knows that an external world exists.