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Descartes' proof of the existence of material objects


To: Max W.
From: Geoffrey Klempner
Subject: Descartes' proof of the existence of material objects
Date: 26th August 2010 13:10

Dear Max,

Thank you for your email of 20 August, with your essay for the University of London Modern Philosophy module, in response to the question, 'Give a critical account of Descartes's argument for the existence of material things.'

There is a problem with how one should take this question. On one reading, you are being asked to give a critical evaluation of every stage of Descartes' argument in the Meditation up to the point where he claims to establish the existence of material things. So we have hyperbolic doubt -- the evil demon hypothesis -- the cogito, the proof (or rather proofs) of the existence of God (including discussion of the alleged Cartesian circle), then finally as the capstone to this chain of inferences, the claim that 'God would not deceive me' into thinking that material things exist in space, when in fact there is no space nor material things external to the mind.

Common sense tells me, however, that this is far too much to encompass in one essay (although you make a brave try). It's more like half a dozen essays.

As a rule, I never look at the examiners reports, so you will have to check what they say about this. If I was responding to this question in the exam, I would quickly run over the various links in the chain, and then home in on the crucial step: Material things exist because that is what we are ineluctably led to believe by the evidence of our senses, and God is not a deceiver. QED.

You mention Berkeley very briefly. I would have thought that the Berkeleian view of the objects of perception as mental ectypes of archetypes existing in the mind of God -- in effect, the theory of a benevolent demon -- is the proposition which is, or ought to be, the main target of Descartes' argument. He's already considered this (in effect). But this would be 'deception', wouldn't it? But what is deception? Why, for that matter, shouldn't God deceive (if it is for the best, as in the story of Abraham and Isaac -- good point)?

We are talking about material things in general, of course. We do make errors in our perceptual judgements, and Descartes in Meditation 6 works hard to fill this apparent lacuna in his account of 'God who is not a deceiver'. The laws of nature being what they are, it is inevitable that sometimes we will be led into error; although he fudges the question of what it would be to act 'responsibly' in one's perceptual judgements. (Surely, it can't be that we should *never* make a judgement whenever there is the slightest possibility of error.)

The crucial point, however, is that matter and space must exist, or we would be the subjects of a perpetual deception. Why?

You spend a lot of time on the question of God's alleged 'perfection'. The relevant point here has to do with his not being a deceiver. The question of how perfection figures in Descartes' two arguments for God's existence isn't relevant (at least on my reading of the question).

In that case, we can bracket the wider issue of just what perfection means when applied to God and focus on God's benevolence, and the implication that therefore he is not a deceiver. Why shouldn't it be 'for the best' that we believe in the existence of material objects in space, even though, in reality these things do not exist?

Incidentally (before I forget) we need to pause at this point to consider your claim that Descartes' proof of the existence of material things is 'lopsided'. This is an argument I haven't seen before. The objection, if I've got this right, is that half the human race (or however many don't believe in God) are 'condemned to perpetual doubt' about material things, because they have no basis on which to conduct the necessary proof. That's too bad. Who do we blame for that? Descartes would say that this isn't God's fault. He has provided ample evidence of his existence, and if half the human race fail to use their God-given capacity for judgement in the way they were designed to then it's their fault, not God's.

The best case I can make on behalf of Descartes (and against Berkeley) is that a 'responsible use of judgement' is precisely what leads us to believe in material objects. You don't need to be a philosopher to grasp the nature of reality, although you need to do philosophy in order to grasp the justifying arguments for our common sense metaphysic of minds and bodies. If material things didn't exist this would be deception, for no valid purpose.

There's more to say. I do think that the beeswax argument, which you cite, is relevant, because it is here that Descartes explains his concept of perceptual 'judgement', distinguishing it from the faculty of imagination. The concept of a material substance is a priori, even though we know about material substances a posteriori. You could say that judgement is intrinsically metaphysical, in that it operates with categories which cannot be merely derived from experience: a point which Kant was later to expand on.

All the best,