(This is a dialogue between Jack and Bob about Descartes, his resistance to the claim that reason is a matter of logical argument, and what zombies have to do with 9-11)
Bob: What have you come up with on Descartes?
Jack: You remember the business Descartes has in his Meditations about dreaming, where he says, you know, if I’m asked to tell the difference between my sitting in my study writing and my lying in bed dreaming I’m sitting in my study writing, I can’t do it. This is what’s called the ‘dream argument.’ The conclusion, according to Descartes, is that we don’t know if we are sitting in our study writing, or anything else.
Let me see if I can find that spot in my book, …here,
5. Though this be true, I must nevertheless here consider that I am a man, and that, consequently, I am in the habit of sleeping, and representing to myself in dreams those same things, or even sometimes others less probable, which the insane think are presented to them in their waking moments. How often have I dreamt that I was in these familiar circumstances, that I was dressed, and occupied this place by the fire, when I was lying undressed in bed? At the present moment, however, I certainly look upon this paper with eyes wide awake; the head which I now move is not asleep; I extend this hand consciously and with express purpose, and I perceive it; the occurrences in sleep are not so distinct as all this. But I cannot forget that, at other times I have been deceived in sleep by similar illusions; and, attentively considering those cases, I perceive so clearly that there exist no certain marks by which the state of waking can ever be distinguished from sleep, that I feel greatly astonished; and in amazement I almost persuade myself that I am now dreaming.
I have thought that the issue here was whether our senses are reliable. Some people have said that they are, others that they are not. I am persuaded that the senses aren’t at issue here as much as another aspect of the argument. Rather than our senses, Descartes puts into question his understanding of reason as being a matter of logical argument. Descartes assumes, I think with some powerful arguments, that our reason is a matter of logical argument and on that view he has trouble distinguishing sitting with dreaming he is sitting.