To: Ignatius U.
From: Geoffrey Klempner
Subject: Dialogue between scientist, priest and philosopher
Date: 7 November 2001 15:27

Dear Ignatius,

I have now read your first assignment for the Philosophy of Mind program, 'An 'imaginary dialogue between a scientist, a priest and a philosopher concerning the nature and existence of the soul, illustrating what is characteristic about the approach of philosophy.'

I am sorry that you have had to wait so long for my response. Unfortunately, your letter did not have sufficient postage (it had a first class stamp, but the correct second class postage was 6 Pence more) and I found a note from the postman saying that I would have to collect the envelope from the sorting office. As the sorting office is quite a distance from my home, I was not able to collect the envelope for several days. Had I been at home when the postman came, this would not have happened!

All of my students who have previously tackled this question have cast the scientist in the role of the materialist who denies the existence of the soul, preferring instead a 'scientific' explanation of human behaviour. Your dialogue is original, in that your scientist Marie does believe in a soul, but does not regard this belief as inconsistent with science. (On a couple of occasions a character 'Florence' appears, but I assume that Florence=Marie. I think what happened was that the character was originally called 'Florence' and then you decided to change the name.)

Marie takes the view that Descartes 'started his whole philosophy from a very logical beginning...Cartesian dualism showed that the mind and the body were different substances. He said that he could doubt the existence of his body but not his mind [soul] and then went on to show his link to this Supreme Being - God.'

Now there is a question here - which was raised by some of Descartes' contemporaries - of how interaction between a physical substance (the body) and a non-physical substance (the soul) can take place. The philosopher Malebranche denied that the soul interacts directly with the body, proposing instead that the changes are brought about or 'occasioned' by God's will.

There are two points to make about the interactionist theory. Cartesian physics differs from Newtonian physics in one very important respect. Newton stated in his famous Laws of Motion that a body 'continues in a state of rest or uniform motion in a straight line unless acted on by a force'. A century prior to Newton, however, Descartes thought only that the momentum of a body is conserved. So, for example, when a ball rebounds from a brick wall, Descartes did not recognize that the wall exerts a force on the ball which causes it to change direction. (This is not an obvious point, by any means, and it took a genius like Newton to see it.) Thus Descartes was able to argue, correctly in the light of his own incorrect physical theory, that the soul brings about changes in the motions of 'animal spirits' - Descartes believed that this took place in the pineal gland in the brain - without any physical force being exerted. This is tied in with Descartes' view of matter as defined purely in terms of its geometrical properties, a point on which he was later criticized by the philosopher Leibniz, a contemporary of Newton.

From this account, it looks as though it must be considerably harder for a scientist who accepts Newton's Laws of Motion to embrace Descartes' theory of mind-body dualism. In terms of contemporary physical theory, mind-body dualism violates the principle of conservation of energy. An effect which requires the input of energy (changes in the motions of animal spirits) is brought about although no physical energy is exerted.

Now, there are different ways in which a present-day believer in science who also believes in a non-physical mind might respond to this challenge. One way is to embrace the view which in the program I call 'epiphenomenalism', which holds that the mind consists in non-physical events of consciousness produced by the physical brain. This causation is 'one-way'. When the body moves, the cause is a state of the brain, which also produces the consciousness of making the decision to move.

Another way to hold onto dualism might be to appeal to quantum mechanics, though the details of this are obscure. The general idea is that although the brain obeys physical laws of cause and effect, there is sufficient 'indeterminacy' in the physical workings of the brain to allow changes which do not have any physical cause.

The other focus of your dialogue is the interesting connection between Plato's view of the soul and that of Descartes.

You are right to imply that the main difference between Plato and Descartes is that Plato does not hold that the soul is a substance. In Plato's theory the soul is 'akin' to the forms, so that it would be truer to say that the soul is more like an abstract idea, which unlike the Forms retains a nugget of individuality. This is not dissimilar to the Pythagorean theory of the soul as an 'attunement', although interestingly, Plato, through the mouthpiece of Socrates, criticizes the Pythagorean theory of the soul as an attunement in the dialogue 'Phaedo'.

- A well constructed dialogue which raises some interesting questions.

All the best,

Geoffrey