G.E. Moore's response to Descartes

In G.E. Moore's "Proof of an External World," he gives a really simple argument that he thinks proves that at least two things exist and have existed in the past. He holds up one hand and says "Here is a hand." He holds up another hand and says "Here is another." And then he concludes that at least two things exist in the world.

Now maybe this doesn't look like much of an argument. Let's look at the form. It's something like this.

1. Moore's left hand exists.
2. Moore's right hand exists.
3. Moore's hands are things.
4. So two things exist (at least).

I added the third premise. But this looks like the basic argument. And on top of this Moore wants to let people know that he can give this truth for the past. So, like this.

1. Moore's left hand existed in the past.
2. Moore's right hand existed in the past.
3. Moore's hands are things.
4. So (at least) Two things existed in the past.

Maybe so far you think this is stupid, perhaps wondering why I would be interested in this or Moore would be writing this etc. But at least some people's aversion to this, perhaps yours, is quite similar to the kind that Moore has toward this issue.

Moore is basically giving a commonsense response to what philosophers feel like is such a problem. He doesn't think it's much of a problem, actually. He's responding particularly to Kant, but he believes this is a possible rebuttal to any kind of skeptical argument.

This is what Moore says about the skeptics.

[W]hat they really want is not merely a proof...but something like a general statement as to how any propositions...may be proved. This, of course, I haven't given; and I do not believe it can be given: if this is what is meant by proof of the existence of external things, I do not believe that any proof of the existence of external things is possible.

What Moore is saying is the kinds of ordinary sentences we say and think can't all be justified. Like, for example, I can't just give a justification in terms of some other kinds of ordinary sensory evidence about how I know that I'm sitting in bed typing this on my laptop.

Moore goes on, responding to Descartes.

How am I to prove now that 'Here's one hand, and here's another'? I do not believe I can do it. In order to do it, I should need to prove for one thing, as Descartes pointed out, that I am not now dreaming. But how can I prove that I am not? I have, no doubt, conclusive reasons for asserting that I am not now dreaming; I have conclusive evidence that I am awake: but that is a very different thing from being able to prove it.

Moore means, perhaps, that he and I and you and everybody can know a lot of things but not be able to prove them. So, according to Moore, we can't prove that we're not dreaming, but, so it seems, that does not mean we don't know many other things.

In Moore's "Four Forms of Scepticism" he talks about something pertinent to this issue. He talks about the degree to which we are certain about certain statements as opposed to others. In this essay, he is responding to philosopher Bertrand Russell who accepts some philosophical premises that support a skeptical conclusion about what we know. But Moore argues that, at least in his mind, these premises are less certain than Moore ordinary premises, like 'I have a left hand.' He writes: "It seems to me more certain that I do know [e.g.[ that this is a pencil and that you are conscious, than that any single... [philosophical] assumption is true... I do not think it is rational to be as certain of any of of these... [philosophical] propositions, as of the proposition that I do know that this is a pencil. And how on earth is it to be decided which of the two things it is rational to be most certain of?"

How does this kind of thinking work with Descartes' orginal argument? Moore doesn't address it head on in his "Proof..." essay nor in "Four Forms..." but he does in "Certainty." But let's see.

First, I'll give the short form of Descartes' argument.

DESCARTES' ARGUMENT
1. If I know that I'm doing what I think I'm doing right now, then I can't possibly just be dreaming I'm doing what I think I'm doing.
2. I could be dreaming I'm doing what I think I'm doing.
3. So I can't know that I'm doing what I think I'm doing.

I'll fill it out a little differently using Moore's specific premises in the essay "Certainty." Same basic idea, but slightly different in expression.

DESCARTES' ARGUMENT (MOORE'S REITERATION)
1. If I know that I am standing up, then I do know that I am not dreaming.
2. I do not know that I am not dreaming.
3. So I don't know that I am standing up.

More has an interesting reply. He says he can actually accept the first premise. He writes:

But this first part of the argument is a consideration which cuts both ways. For, if it is true, it follows that if I do know that I am standing up, then i do know that I am not dreaming. I can therefore just as well argue: since I do know that I'm standing up, it follows that I do know that I'm not dreaming; as my opponent can argue: sinceyou don't know that you're not dreaming, it follows that you don't know that you're standing up. The one argument is just as good as the other, unless my opponent can give better reasons for asserting that I don't know that I'm not dreaming, than I can give for asserting that I do know that I am standing up.

He thinks that Descartes or the Cartesians just can't give the kind of support they would like to to the second premise. Their support for the second premise seems to be something like the following. We've all had experiences when we've thought we've been dreaming but weren't actually. Moore thinks this is tantamount to claiming knowledge of dreams and having dream experiences in the past. In the same way that Moore argued against abstract philosophical propositions about which he is less sure of than concrete ones he can say that he doesn't see how it is logically possible that somebody both be dreaming and know that he has had previous experiences of such. He doesn't see how both are as likely as knowing now you're not dreaming. He writes, "The conjunction of the proposition that I have these sense experiences and memories with the proposition that I am dreaming does seem to me to be very likely self-contradictory."

So, here's a kind of recap with regard Descartes' argument and Moore's argument. Moore or anyone who'd been sympathetic to Moore's way of thinking could accept the first premise. But instead of getting to the second premise, Mooreans could adopt a different second premise, namely "I know that I'm doing what I think I'm doing right now." Furthermore, they could support it, for example, by saying that they have ample ordinary sensory evidence which in ordinary circumstances counts as knowledge. So what the Moorean can do is invert the reasoning of Descartes. So here goes the Moorean argument.

MOOREAN ARGUMENT
1. If I know that I'm doing what I think I'm doing right now, then I can't possibly just be dreaming I'm doing what I think I'm doing.
2. I know that I'm doing what I think I'm doing right now.
3. So I can't possibly just be dreaming I'm doing what I think I'm doing.

Such is the Moorean strategy, and such is one reply to the skeptic.

Whaddaya think so far? Are you convinced?