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Descartes 3

Mind Body Dualism

Now let us turn to Descartes' account of the relation of the mind and the body. This involves three topics --- mind body dualism, proofs for the real distinction between mind and body, and two way causal interaction.

Descartes in Meditation II concludes that he is in essence a thinking thing (res cogitans), and that it is possible that he exists without a body. He recognizes, however, that to conclude from this that his mind is really distinct from his body would be fallacious. The Stoic paradox of the masked man illustrates the fallacy. If a person sees their father, they will very likely recognize him. If the same person is then shown a masked man, they may doubt that this is their father. Still, the masked man might be their father. So, to conclude that the father and the masked man are really distinct because one cannot doubt in one case but can in the other is clearly fallacious. The case is precisely the same for Descartes in relation to his mind and his body in Meditation II.

Descartes does make some further progress in respect to this problem in Meditation II -- he determines, as noted above, that the essence of body is to be flexible, movable and extended. Thus it turns out that the essence of mind and the essence of body are two different things. Minds are in essence thinking things, bodies are in essence space occupiers, movable and flexible. This is the basic doctrine of Cartesian dualism with respect to mind and body -- bodies and minds are different kinds of entities. One motivation for this distinction is an interest in the Christian doctrine of immortality. Descartes originally intended the Meditationes de Prima Philosophia to include a proof of the immortality of the soul. He does not entirely succeed in this, but perhaps takes some steps towards the achievement of such a goal. One of these steps involves proving that there is a real distinction between the mind and the body, i.e. that the soul can exist independently of the body.

Proofs for the Real Distinction between Mind and Body

In Meditation VI Descartes gives two proofs for the real distinction between minds and bodies. One of these involves a contrast between the simple nature of the soul and the complex nature of the body. The other picks up the materials which Descartes had provided for himself in Meditation II and III and puts them together into a proof. From Meditation II Descartes takes the fact that the essences of mind and body are distinct. From Meditation III he takes the language of clear and distinct ideas, and the existence of God and from God's omnipotence concludes that God could make distinct any two things which I clearly and distinctly perceive could be distinguished. Since the essence of mind and body are different and these ideas are clear and distinct, it follows that God could make them distinct. Descartes concludes that they are in fact distinct. There is a debate in the scholarly literature over whether this last step is justified.

Two Way Causal Interaction

Supposing that minds and bodies really are distinct from one another, how do they relate to one another? Minds are thinking things which are not extended, bodies are extended and do not think. Descartes' answer is that minds are effected by bodies in perception and that bodies are effected by minds in action. Thus, when I see a tree, the tree is causing light rays to hit my eye, this information is taken by the animal spirits up to the brain, and passed through the pineal gland to the mind where it is perceived as the idea of a tree. On the other hand, if I decide to lift my arm, my mind issues a command which is passed through the pineal gland to the brain, and from the brain the animal spirits are animated in such a way that my arm raises. This is two way causal interaction. It is two way because the mind causally effects the body in action, and the body causally effects the mind in perception. It is causal because the process is causal and not say logical or aesthetic or some other kind of relationship. It is interaction because it is one kind of entity acting on another, that is minds on bodies or bodies on minds.

The Mind Body Problem

After Descartes articulated this theory, philosophers in the next generation (and thereafter) were struck more by the difficulties of the theory of two way causal interaction than by what it explained. How can a mind, which is immaterial, cause any kind of change in a body at all? How can a body, which is material and occupies space, affect something which is immaterial and does not occupy space? It is possible to evade some of these difficulties in various ways. However, for Descartes the difficulties are compounded by his heirloom theory of causality which plays a crucial role in Descartes' proof for the existence of God. This theory holds that the effect inherits something from the cause. This explains the connection between cause and effect. Given the real distinction, however, it appears that there is nothing which can play this role for minds and bodies -- what do they have in common?

The result was that philosophers tried two distinct but connected strategies to avoid committing themselves to two way causal interaction of minds and bodies. One of these strategies is reductionism. The other is to allow the appearance of two way causal interaction while denying its reality. Idealism, materialism and occasionalism are all examples of reductionist strategies. Materialism, for example, says that there are no immaterial minds. Minds are just brains. So, there are only bodies and hence not mind body interaction. Idealism, on the other hand, holds that there is no matter, and hence no bodies. If there are no material bodies, presumablby there cannot be two way causal interaction! But even the idealist holds that bodies exist, they are simply not material. Rather bodies are simply collections of ideas in minds! So the idealist might allow that there is the appearance of two way causal interaction without it really being so. There were also dualists who held that there only appeared to be causal interaction because, in fact, God was the only cause. This doctrine was called Occasionalism.


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