In Descartes philosophy Mind & Matter are two substances which he then found difficult explain how they affected each other.

This, on the face of it seems wrong. Conventionally, one supposes one has a mind, and that ones body is real; I think of moving my left foot one inch forward, and it does; empirically & observationally there appears no impediment between thought an action, between mind and body and thus matter.

Hence this cannot be Descartes starting point. Perhaps the key concept here is substance.

What is substance?

It is free of all accident, and is causally self-subsistent.

From this one deduces that mind and matter are substances. The question is are they the same substance. Where there is two, the possibility of reducing to one presents itself.

Now given that we have stipulated that a substance is causally self-subsistent, and given what we have observed above, mind moving matter, it seems that matter must be of the same substance as mind.

But there is another distinction that holds for substance, to remove all accident is to uncover the essence of a substance.

For mind differs in quality from matter in an essential way; mind has qualia, matter does not appear to do so. So these two substances are essentially different, yet they are causally active on each other. For if my mind is causally inert, then my mind, my stream of consciousness moves nothing - a quotation from Yeats is opposite here:

Our master Caesar is in the tent

Where the maps are spread,

His eyes fixed upon nothing,

A hand upon his head.

Like a long-legged fly upon the stream

His mind moves upon silence.

This is Descartes riddle.

  1. If the distinction of qualia holds then one must explain causality between two differing substances.

  2. If the observation of causality holds, then one must explain why qualia is not essential.

From 2, we can derive the doctrine of Idealism, all is mind; or that of physicalism, that all is matter.

From 1, we derive Spinozas system.


a. Is this a correct summary of Descartes position and how does he himself solve it?

b. Was Descarte the first to present this position, or was it well known in Medeival Theology?

2 Answers 2


Firstly (a)

Descartes discusses this problem in, among other works, the Meditations, although he obviously does it in different terms to you. For example 'qualia' is a relatively recent term. It might be just as well to think of Descatres dualism as between body and soul, which must be made of two different substances as the soul can outlive the body after death.

Now for a very quick run through the meditations;

First he discards all knowledge he currently has, including knowledge of the existence of the physical, as uncertain as he could be dreaming or being tricked by an evil demon. For example, there could be an evil demon who makes him think he has a physical body when actually no such thing exists.

Now from a foundation of nothing he uses his famous "cogito ergo sum" (I think therefore I am) to assert that he must have a mind. Using this as his first building block he goes onto to claim that he has a "clear and distinct idea" of God, who must exist, as God would never trick Descartes into having a clear and distinct idea which wasn't actually clear and distinct (this is famously circular).

Having decided that both mind and body exist, Descartes did need to explain the very apparent causality between the two. He did so by claiming that animal spirits flow into the brain and back again through the pineal gland. For more on that see this SEP entry: http://plato.stanford.edu/entries/pineal-gland/

Secondly (b)

Descartes was the first person to think about this problem philosophically (at least that I'm aware of). I'm sure others in the past must have wondered about the mind-body problem before him, but his method of doubt and his 'cogito' secured him philosophical fame for his treatment of substance dualism.


The riddle of mind and matter must have always perturbed humans. This would appear to explain the origin of religion: A response to the awe that space, time, and events have caused humans; which leads naturally to the attempt to resolve these perturbations in one swoop.

Descartes may have been first to raise this issue in a manner that is researchable. I have attempted to define energy as the link between mind and matter. And to present spirit and soul as other forms of existence; all four, 4 of which need to be acknowledged, to reconstruct reality objectively. You may like to follow these links: https://www.academia.edu/s/af66213163 http://www.slideshare.net/peteranyebe/making-global-leaders-an-hr-imperative

  • 2
    Welcome to Philosophy.SE! This post seems to say things about Descartes's Riddle without saying what it actually is. Feb 15, 2016 at 14:08

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