Cartesian mind-body interactionism revisited

Jennyfer asked:

Hello, I have a question about Descartes’ dualism. A lot of people have argued that with his dualism view comes the problem of interactionism: How can the mind have an influence on the body since it is a non-extended substance?

I was wondering how Descartes has defended his opinion when facing these criticisms. Did he consider that the union of the mind and the body (lying in pineal gland)was the reason of this interactionism? How did he explain that?

Answer by Hubertus Fremerey

You refer explicitly to how Descartes tried ‘to explain the dualism’. Juergen Lawrenz answered to that. I would like to add some light to the matter itself. If you listen to, say, a piano sonata: Where would you put the ‘beauty’? Is it in the sound-waves? Is it in the piano? No, it is in your feelings, i.e., in some neuronal states of ‘good feelings’. But at the same time, people are debating ‘the nature of beauty’. Thus you have three different aspects here: The material ‘sound waves’ and ‘neuronal excitements’, then the ‘feelings’, and finally a formal theory which is neither on sound waves nor on feelings, but on some formal descriptions. But the formal descriptions appeal to our understanding. Thus there seems to be only one ‘substrate’ (‘matter’) — the neurons — but two different immaterial ‘concepts’ — the feeling and the evaluation. So even the concept of ‘mind’ is in this picture split in two — the feeling mind and the evaluating mind. The evaluating mind surely is not in the pineal gland, but is commenting on the feelings, since if there were no feelings there would be no concept of beauty either. And if there were no sound waves there would be no feelings.

And what did Beethoven hear when he was deaf — writing his great last sonatas and symphonies?

Your question is a historical one: ‘what did Descartes think?’. My answer added some modern considerations on the problem underlying his question. We still tend to ‘substantialize’ formal things. Beauty is a form, not a substance, and evaluation is a process, not a matter either and not a form. To cover both immaterial ‘things’ — beauty and evaluation — people invented ‘the soul’. The concept of the soul is even more complicated than that, since some people claim an ‘immortal soul’ which is neither ‘feeling beauty’ nor ‘evaluating beauty’. But I leave it at that.

This is just a hint at how complicated things look when we try to put names to experiences. This is what Descartes tried to do: Make sense of the strange experience of a dualism. There is much more to that of course. I did not even touch emotions and the will etc., which too belong to ‘the soul’.


Answer by Craig Skinner

Substance dualism is the weakest point in Descartes’ philosophy — the ‘ghost in the machine’ view of the mind-body relation. as Ryle described it.

How the two substances could possibly interact is unexplained by Descartes or by anybody else. It makes little difference whether the interaction is considered to be in the whole body or in part of it, such as the brain or the pineal gland.

Descartes chose the pineal as the seat of the soul because he thought it was unique to humans, and it had no other known function. He was far less keen on it when he later learned that dogs, for instance, also have pineals: he considered that dogs (and other animals) had no thoughts.

The last serious attempt at a substance dualism explanation was by the famous neurophysiologist Eccles some 40 years ago. Instead of Descartes’ mind influencing animal spirits flowing through pipes and pores in the pineal, Eccles had the mind influencing impulses flowing through neurones, and transmitters crossing synapses, but neither man could explain how the immaterial mind could do this.

How did Descartes defend his view? As best he could — unconvincingly.

His attempt is nicely illustrated in the 1643 letters between Descartes (D) and his very astute distance student, Princess Elisabeth of Bohemia (E), a kind of 17th Century sustained Ask a Philosopher exchange.

Here are selected sequential comments from the correspondence (trans. Jonathan Bennett, online at

"E. Given that the soul of a human being is only a thinking substance, how can it affect the bodily spirits, in order to bring about voluntary actions?

How a thing moves depends on how much it is pushed, the manner in which it is pushed, and the shape of the thing that pushes. The first two require contact, the third that the thing be extended.

Your notion of the soul excludes extension and an immaterial thing can’t touch anything.

D. How do we think the weight of a rock moves the rock downwards? We don’t think that this happens through contact. But we have no difficulty in conceiving how it moves the body, nor how the weight and the rock are connected. I believe that this notion was given to us for conceiving how the soul moves the body.

E. I don’t see how the idea about weight can guide us to how the soul can move the body. The old idea about weight may be a fiction produced by ignorance of what really moves rocks toward the centre of the earth.

D. The soul is conceived by the intellect, the body by the intellect aided by the imagination, the union is a very dark affair when from the intellect aided by the imagination, but bright when the senses have a hand in it.

People who never come at things in a theoretical way and use only their senses have no doubt that the soul moves the body and that the body acts on the soul. What teaches us how to conceive the union is the ordinary course of life and conversation, not meditating or studying things that exercise the imagination.

It seems to me that the mind can’t conceive the soul’s distinctness from the body and its union with the body clearly at the same time, because to conceive them as one and at the same time two is contradictory.

E. The senses show me that the soul moves the body, but as for how it does so, the senses tell me nothing more than the intellect and imagination do."

As you can see Descartes appeals to dubious analogy, alleged common sense, and inconceivability.

In his 1648 correspondence with Burman (B), he simply begs the question:

"D. Nature teaches me — through these sensations of pain, hunger, thirst and so on — that I am not merely in my body as a sailor is in a ship. Rather, I am closely joined to it — intermingled with it, so to speak -so that it and I form a unit.

B. But how can this be? How can the soul affect and be affected by the body when their natures are completely different?

D. This is hard to explain: but here our experience is sufficient, because it declares the fact so loudly that we simply can’t deny it."

Had Descartes not tried to defend substance dualism, we might have paid more attention to his other views on cognition and emotion, because his discussion of connectionism in the pineal anticipates modern ideas such as Hebbian learning (‘cells that fire together wire together’) and distributed representation, while his views on the passions anticipate modern views on embodied cognition. Descartes was a pretty good scientist as well as a great mathematician and philosopher.


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