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What leads Descartes to posit an evil demon?


To: Cynthia G.
From: Geoffrey Klempner
Subject: What leads Descartes to posit an evil demon?
Date: 21st May 2009 09:51

Dear Cynthia,

Thank you for your letter of 10 May, with your essay for the University of London Introduction to Philosophy Diploma module, in response to the question, 'I shall suppose that... some malicious demon of the utmost power and cunning has employed all his energies in order to deceive me.' What leads Descartes to make this supposition?

This is without doubt an excellent piece of work and possibly the best essay I have received on this topic. I don't too much like the 'notes' style, but I think you could get away with this in an exam, especially since it enables you to lay out Descartes' arguments so perspicuously.

Regarding the content, I think you give more than the question asks for, although there is room for debate over how one interprets 'leads to'. On my reading, the question is asking you to give the logical sequence of steps which necessitate the evil demon hypothesis. You have done this, but you have also offered background information which explains Descartes' motivations in setting out the argument in this way. I don't think that the question asks for this, although another question might.

(A general observation: When commenting on essays I will always stress the issue of relevance. However, as these essays are also a way for you to assimilate the material, you may feel the need to give more than the question asks for -- especially since you don't know how the exam questions will be worded. You might consider writing notes for your own use, and then using these as a basis for writing essays which are sharply focused on the question.)

There is an important sense in which Descartes is forced to have recourse to the evil demon. He needs this device in order to establish the conclusion that he wants to establish: namely, the identification of knowledge which is immune from doubt and which therefore can serve as a foundation for 'science'. So how does he get there?

In laying out the sequence of sceptical hypotheses, there is something which arguably you have missed and which is essential to explaining how the evil demon hypothesis arises.

Superficially, the structure of the 1st Meditation seems to be this: Descartes tries an argument (argument from illusion, senses are unreliable). There is a response to that argument. So Descartes is forced to go further and consider the hypothesis that he is dreaming. But that still leaves a loophole: the sheer improbability that the experience I am having now is a dream, given belief in an omnibenevolent God. The evil demon plugs the gap.

However this may work as a clever heuristic device, one might still ask why doesn't Descartes just cut to the chase and give his strongest argument straight away?

The answer is that he has established something of importance, which is required in order to give coherence to the evil demon idea. That is the nature of 'experience' as something which exists in us, subjectively, independently of how things are in the external world. I seem to see a square tower in the distance, therefore I have the subjective experience of a seeming-square-tower, regardless of whether the tower is in fact round or square, or indeed whether there is anything out there at all.

In your essay you do make two important points which are relevant, although these are just noted rather than explored. That Descartes assumes logic and the reliability of memory; and the connected claim that he (and the reader) is sane, not a madman. These assumptions point to what many would regard is the fatal weakness in Descartes' position, which is connected with his conception of subjective experience, whose indubitability is the cornerstone of his argument in the 2nd Meditation.

If we take the argument from illusion to its logical conclusion, then memory is just another experience. Memories can be wrong. This isn't just a sceptical worry; the very notion of a difference between 'true' and 'false' memory dissolves. Moreover, the idea that I have sound judgement itself comes into question when one considers that from the Cartesian perspective I am the final authority on whether or not I am correctly following the rules for the use of the words in my language -- a language Descartes assumes would remain meaningful even if none of my beliefs regarding the external world are true. Whatever seems 'right' to me IS right, so the very notion of truth dissolves. (This is the bare bones of Wittgenstein's argument against a 'private language'.)

In your conclusion you state, 'there is evidence of suppressed assumptions which he thinks the reader shares -- for example, in his arguments he presupposes that he actually exists and is thinking'. You go on to accuse Descartes of 'circularity' in his claim regarding the Cogito. I think this is too strong. It is true that Descartes doesn't raise the question, 'Do I exist?' Given what I've said about memory, it could be argued that he cannot assume this. However, this does not undermine the validity of the argument, 'If an evil demon deceives me, then I exist' (or, at least, I exist now).

All the best,