"Knowledge and Reality" -- spring '07: Did Moore really prove that there is an external world or did he miss of the point of Descartes' "Dream Argument"?
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Descartes argues that we cannot trust our senses because there is a chance that we may be dreaming. Sometimes when one is dreaming it feels as if they are awake, and a vice versa. If there is nothing to distinguish being asleep from being awake, then Descartes argues that we can never be sure that we are not dreaming. And if we can’t be sure that we’re not dreaming, then how can we be sure that our perceptions are true? And if we can’t be sure of our perceptions, then how do we know there is an external world?

G.E. Moore in “Proof of an External World” argues that there is an external world. Moore simply shows his hands to prove his argument. Since we see his hands, obviously they exist. Since his hands exist, obviously the external world exists. Moore feels that by doing this he has proved there is an external world because he has a made a “logically rigorous argument.” A “logically rigorous argument” is based on three things. The first is that the premises must be different from the conclusion. The second is that the premises must be known to be true. The third is that the conclusion must follow from the premises.

Moore feels that because his argument was “logically rigorous” it proved his point. But when one looks at the three rules for this kind of argument from Descartes point of view, the argument may lose some validity. Let’s look at each of the three rules separately from Descartes’ point of view.

The first is that the premises must be different from the conclusion. Moore started off by saying that his hands existed and concluded by saying the external world existed. If one was dreaming though, these two things could mean the exact same thing. I’ve often had dreams where I say something and some repeats what I said, but when I wake up I realize they said something completely different from what I had said. So, if one is dreaming, then Moore’s premises and conclusion may be the same thing.

The second is that the premises must be known to be true. Moore believes that there is truth in the existence of hands. But if one is dreaming, then even if they are seeing hands, those hands might not actually be there. I don’t think that Descartes would agree that Moore’s premise is known to be true for that one reason.

The third is that the conclusion must follow the premise. If it is unclear whether or not the hands one is seeing really exist, then how can one be sure that the external world exists? Moore’s conclusion doesn’t really seem to follow his premise if there is that uncertainty there.

Moore’s proof that the external world exists may have been a proof for other common sense philosophers, but when it comes to proving it to philosophers like Descartes, Moore has completely missed the point. You can’t prove something to someone using your way of thinking. If you’re going to prove something to someone, you can’t just assume that they’ll agree with your methods. How does shaking around one’s hands prove to a person who isn’t even sure that he is awake that hands exist?
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