G. E. Moore’s “Proof of an External World”

Moore begins by saying that, even though Kant claimed that there could be only one possible proof of the external world (the one Kant gave), to Moore it seems that many perfectly rigorous arguments can be given. Suppose he holds up his right hand and says, “Here is one hand”; and then he holds up his other hand and says, “Here is another hand.” To Moore, this is a perfectly rigorous proof of the proposition “There now exists two hands.”

Three things are necessary for a proof to be considered rigorous. (1) The premises must be known; (2) the conclusion must be different than the premise(s); and (3) if the premises are true, then the conclusion must be true. 

Moore says that the first requirement is met, because certainly he knows, when he is holding up one hand and then another, that “here is one hand” and “here is another”. He knows this as well as he knows that he is standing there. Surely there is nothing more certain than that he is holding out his hands.

The second requirement is met, according to Moore, although he recognizes that there might be some people who would think the conclusion “There exists a hand” to be no different than the premise “Here is a hand”.  Moore claims that the conclusion is different from the premise because the conclusion could be true even if the premise is false. So, the premise and the conclusion are not identical.

The third requirement is also true, because if the premise “Here is a hand” is true, then surely the conclusion “A hand exists” is true.

He points out that, if this argument is a perfectly rigorous one, as he thinks it is, then it should be obvious that many more can be given.

He says that his argument is the kind that we would accept as a perfectly good argument in everyday circumstances. If someone were to question whether there were three typos on a certain page in a book, it would be a perfectly acceptable proof to open the book and say “Here’s one typo, here’s another, and here’s the third.” That’s be acceptable proof.

Something people are interested when they want to prove the external world is to not only prove that external objects exist now, but that they existed in the past as well. But, Moore claims, many proofs can be given of things existing in the past. The proofs will resemble the proofs of things existing now, but they will also have important differences. One such proof could be: You remember that a few minutes ago I held up one hand, and then the other, therefore, two hands existed in the past.

But Moore is perfectly aware that many philosophers will not find his proof convincing. They want something more than this, but it can be difficult to know exactly what else they want. One things that they probably desire is a proof of the premises of Moore’s argument. But, Moore says, he won’t give one, nor does he think one can be given. To prove that Moore really held up his hands would require, as Descartes pointed out, that Moore prove he isn’t dreaming. Moore doesn’t think he can do that. But he can know, he can have conclusive evidence that he is holding up his hands, without being able to prove it. That’s all he needs. 

But another reason they would be dissatisfied with Moore’s proof is that, not only would they want a proof of Moore’s premises, but they think that if he can’t prove his premises his proof isn’t conclusive (so either they think that a rigorous proof requires that the premises be proven or, at least, provable; or they think that to know something means that you can prove it. –MAC). Moore, however, rejects this idea, even though it is common among philosophers. People claim that if you can’t prove something, you can only accept it on faith. But Moore says this isn’t so. You can know something you can’t prove. So, the dissatisfaction of these people is wrong.

 

KEY POINTS

1. According to Moore, to prove that he was holding up his hands would require him, as Descartes pointed out, to prove (not just know) that he isn’t dreaming, which Moore doesn’t think he can do.
2. Moore thinks you can know things you can’t prove.
3. It has been a common view among philosophers, however, that you can’t know things you can’t prove–you can only take them on faith.
4. A test to see if a conclusion is different from a premise (or, if two propositions are different) is to  see if one could be true while the other false.
5. To say that something might be proven to exist (or be true) is to say that that thing might be certain to exist or be true.

Tags: G. E. Moore, proof of external world