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Descartes' argument for dualism in the 6th Meditation


To: Alan M.
From: Geoffrey Klempner
Subject: Descartes' argument for dualism in the 6th Meditation
Date: 22 March 2002 15:54

Dear Alan,

Thank you for your e-mail of 11 March, with your second essay for the Philosophy of Mind program, in response to the question, 'Examine Descartes' argument, in the Sixth Meditation, for the distinction between mind and body. What objections can you conceive being raised against the argument? How would you attempt to defend the argument against those objections?'

As you rightly point out, God plays a prominent role in Descartes' argument. In fact, God plays two distinct roles, which should be distinguished:

1. As guarantor that our clear and distinct ideas do in fact correspond to reality.

2. As a conceptual device express the fact that two given entities closely associated with one another are in fact distinct and not merely different aspects or views of one and the same entity.

Regarding 1., so long as there remains the possibility that 'the evil demon is deceiving me', it is impossible, Descartes thinks, to do philosophy. We cannot draw any conclusions on the basis of what reason and logic demands, because we cannot rely on the soundness of our own reasoning. Similarly, in the empirical case, we cannot rely on our notion of 'best explanation' corresponding to the way the world actually operates.

The response to the worry about philosophy is to say that we can only reason as we reason. To appeal to God is simply redundant. Even if God exists, that does not stop us being convinced by invalid philosophical arguments. This contrasts with the empirical case, where God as the 'designer' of the human mind does real explanatory work. (Arguably, this was later done by Darwin's theory of evolution - a point argued by Peter Carruthers in his book 'Human Knowledge Human Nature': our minds are 'designed' in such a way as to enable us to make reliable predictions about the world around us on the basis of our natural sense of what counts as a good explanation.)

Regarding 2. the point is that when Descartes says, 'It is conceivable that mind and body could be separated by the power of God', all he has to say is that it is conceivable that they could be separated by some sufficiently mighty power. Instead of 'God' he could have said 'the evil demon' or 'super-advanced aliens'.

In other words, the argument rests on a logical point, that if A *is* B, then it is simply nonsensical to conceive of A and B existing apart. So if we can conceive of A and B existing apart (as we apparently do when we consider the hypothesis of a dream-inducing evil demon) then it follows that the statement 'A is B' is false.

Saul Kripke, in 'Naming and Necessity' gives the necessary logical scaffolding to render Descartes' argument convincing, using the distinction between 'rigid' and 'non-rigid' designators. 'Heat is the motion of molecules', according to Kripke, picks out a necessary, and not merely contingent truth. The explanation of its apparent contingency is that in another possible world, the physical phenomenon of heat, the motion of molecules might not have been *felt* as heat. This move cannot be made in the case of 'Pain is C-fibre stimulation', Kripke argues, because it is nonsensical to suppose that there could be a possible world where 'pain was not felt as pain'.

As I see it, the response of the anti-dualist has got to be to question the Cartesian premise, namely that we have a handle on what is given on the 'inside', the quale of red or of pain, which is independent of our knowledge of the physical world.

In this context, Nagel's challenge in 'Physicalism' and 'What is it like to be a bat?' is important, not as another way of arguing for Descartes' conclusion, but rather to cause difficulties for a certain conception of physical monism, according to which 'all the facts' are accounted for by all that can be said about the physical phenomena, i.e. the propositions of science.

In my paper for Shap 2001, 'Truth and subjective knowledge' (Glass House Philosopher I argue that there can be something 'in' us, consistent with a physicalist outlook, which cannot - not even in principle - be described in physicalist terms. 'What it is like' for one's brain to be in a certain state is 'subjective', non-propositional knowledge, which is in principle inaccessible to any subject other than the subject whose brain it is.

At the end of your essay, you propose the familiar 'functionalist' account of mental states, which apparently avoids all the problems of the identity theory. It does so, only because it rejects the Cartesian premise, as I indicated above. However, as you point out, the theory leaves us with the problem of explaining subjectivity. It is not enough to make the point about 'subjective knowledge'. There is a real gap of explanation at the vital point (despite what Dennett says in 'Explaining Consciousness'). At the present time, we really do not know what kind of thing a 'program of the human brain' would be, but merely grasp at crude quasi-mechanical models and metaphors.

All the best,