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Descartes' case for doubt


To: Frank M.
From: Geoffrey Klempner
Subject: Descartes' case for doubt
Date: 26 November 2003 15:42

Dear Frank,

Thank you for your e-mail of 17 November, with your second University of London essay in response to the question, 'In his First Meditation, how does Descartes attempt to show that there is a reason to doubt everything one believes? How successful is this attempt?'

You have written a very good answer to the question. You have carefully explained the various stages of Descartes' argument in Meditation One and you have made sensible comments on each stage. There is not a hint of waffle anywhere in the essay - you get right to the point.

Why on earth should a philosopher should attempt to 'show that there is a reason to doubt everything one believes'? You do say something about this at the end of your essay, along the lines of, 'It's healthy to doubt' etc. However, Descartes clearly exceeds the bounds of healthy doubt. You wouldn't teach school children to remember that it's possible that they are being deceived by an evil demon. It wouldn't serve any purpose other than to make them very upset.

The point is that, given that 'there is a reason to doubt everything', a stronger reason will be needed for not doubting everything. The measurement of success in Descartes' strategy is whether he has achieved his goal of convincing the reader that this stronger reason will be needed. If Descartes is wrong and we are not sick after all - if his arguments for scepticism are bad arguments - then we won't need his medicine (proof of the existence of a non-deceiving God).

It is also true, of course, that in Meditation Two Descartes remembers that there is in fact one thing that cannot be doubted - that he exists, a fact which he conveniently forgot in Meditation One!

That's the only general point I have to make, the rest concerns the details of your responses to each of the four arguments which you identify.

Senses argument

The 'argument from illusion' as it is sometimes called has been used, e.g. by sense datum theorists to argue that whenever we look at any given object (e.g. a tomato) it is always possible that that object is different from the way it appears. So, even if one accepts that not all objects can be different from the way they appear, we would still arrive at the conclusion that the immediate objects of knowledge are not things in the world (as we previously thought) but our own sense impressions, from which a more or less shaky inference to what is 'out there' is required. The most famous example of this is Bertrand Russell in 'The Problems of Philosophy'.

Put in those terms, the argument from illusion seems pretty strong - but is it valid?

Insanity argument

Like you, I wish Descartes had said more about insanity. (I recall coming across a reference to a book by Harry Frankfurt, 'Demons, Dreamers and Madmen'.) Suppose I am suffering from a paranoid delusion. The FBI are after me. You write, 'Don't be so silly' and that's just further proof - you're with them too! From the first person standpoint, there are ultimate limits to what we can discover. Attempting to build my knowledge from the foundations up necessarily leaves out one vital possibility - that from the outside my actions show that I am imprisoned in a world of my own from which I can never escape. Descartes is right that I have to assume that I am sane. But even if it is a necessary assumption, that doesn't make it true. It doesn't amount to a proof that I sane.

Dreaming argument

Good point about the distinctness of dreams. Descartes does need to say more, to make his argument convincing. However, the bigger picture is that 'dreaming' illustrates a possibility that might be realized, not in a dream as we know it, but in something which logically has the same status of a dream - in experiences arising from some source other than perception of external objects. Sound familiar? It is the Matrix scenario.

Descartes' evil demon could be compared with the artificial intelligences that run the Matrix world - except for one not so small detail: Descartes is prepared to consider the possibility that space does not exist. For the Matrix story to make sense, there has to be space (the hero wakes up to find that he is lying in a pod surrounded by thousands of other pods).

If I believe that space exists, has Descartes given me sufficient reason to doubt that belief?

The Divine argument

Like you, I am puzzled by the argument, 'If God did not create me, then I am even more likely to be in error.' One argument Descartes could give might go something like this. In the absence of a Deity, there is no ultimate standard of rationality or logic. Anything goes. Therefore, when I think that X is a good reason for Y, that's just some process happening in the world. There is no reason to think that this process is capable of attaining truth. Imagine if an idiot who knew nothing of arithmetic was given the tools to make a calculating machine. You can press the keys and numbers come up on the screen - they just don't add up. That's the human brain in the absence of God.

All the best,