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Descartes' proof of God in the 3rd Meditation


To: Barry T.
From: Geoffrey Klempner
Subject: Descartes proof of God in the 3rd Meditation
Date: 15 December 2006 11:53

Dear Barry,

Thank you for your email of 10 December, with your University of London essay in response to the question, 'What weaknesses, if any do you find in Descartes' proof of the existence of God in the Third Meditation?'

This is on the whole a very good essay. However, if I was marking this in an exam, I would put a big 'R' (for relevance) in the margin next to the discussion of the Cartesian Circle.

The reason for this is that it is not part of the question of the validity of Descartes' argument for the existence of God, to consider objections to Descartes' strategy of using God as the ultimate guarantee that clear and distinct ideas are indeed true.

There is a danger that you would lose marks, and also lose time. Don't give in to the temptation to give more than the question asks for. (That does not mean you have to give the examiner what he or she expects. It is perfectly possible to surprise the examiner with an answer to the question which they had not anticipated.)

That leaves the causal adequacy principle, and Descartes claim to have a clear and distinct idea of an infinite God.

You say, 'Descartes gives no grounds for rejecting the concept that there could be an indefinitely long chain of ideas.' You are right that he does not offer an explicit argument against this idea. However, it would be within the remit of this essay to look for one. The question is how we decide whether a regress is, or is not vicious.

An analogous question arises in relation to the cosmological argument. Objectors to the cosmological argument point out that there is no logical absurdity about a chain of causes and effects which stretches back infinitely. That may be true. However, someone who puts forward the cosmological argument believes (rightly or wrongly) that the way the world is at the present time is dependent on the way it is at past times, in the way in which, e.g. a link in the chain holding a chandelier is dependent on the links above it. Being infinitely long would not prevent the chandelier from falling to the ground.

In a similar manner, Descartes would argue that making the chain of ideas infinitely long merely defers the question where the idea of God comes from rather than answering it.

At least one twentieth century philosopher has taken Descartes' argument seriously, although not exactly as Descartes intended. Emmanuel Levinas in 'Totality and Infinity' cites Descartes idea of infinity as the model for his argument for the 'otherness of the other' as the ultimate ethical anchoring point for metaphysics. All that we can reason from our own heads is 'thematized' knowledge, or knowledge of the causal order. But such knowledge would never suffice to prove that another person is real, rather than just another 'object' in my world that behaves in various more or less predictable ways.

Another issue, which would not be irrelevant, is the question of our idea of infinity as such. Of course, there is the mathematical definition of an infinite set as one whose members can be put into a 1-1 relation to a proper subset. But this definition is not adequate to explain what it would mean to ask the question, 'Could it be, as a matter of brute contingent fact, that there are an infinite number of physical objects in the universe?' The mathematical notion of infinity is related to a recursive rule. The problem is with contingent or 'brute' infinity, there just happening to be an infinite number of things. (See the excellent book by Adrian Moore, 'The Infinite' RKP.)

So while it is certainly legitimate to question, as you do, whether Descartes really has an idea of an 'infinite God', or merely thinks he has, the problem of where such a 'big' idea comes from is not one that one can escape simply by refusing to allow the coherence of the notion of a deity as such.

Descartes can say this. 'Not everyone thinks they have an idea of God. If you don't think this, then my argument is not going to be of any interest to you. But if you do think that you have an idea of God, then you must either admit that this is a delusion, or you must come up with an adequate explanation of how you were able to acquire this idea.'

The argument that if the idea of God is innate then everyone should have it does not seem to be compelling. You say in that case 'it should be present in every able minded human being'. But that is precisely the point. Most human beings are not 'able minded' in the philosophical sense, even if their minds are fully adequate to meet the demands of daily life. However, by a suitable training in philosophy, one can become better able (as Plato believed when he wrote the Meno) to perceive the ideas that one implicitly has.

All the best,