Descartes on Mind and Matter (16-Oct-2003)

Reading : Western Philosophy II.3 "Supreme Being and Created Things"

Aristotle's views held sway for almost 2,000 years but started to be challenged in the 16th century by, among others, Descartes. Like Aristotle, Descartes was a man of wide ranging interests, who wrote on many subjects, including mathematics and physics. We can see the influence of these subjects on his metaphysical view of the universe.

Like Aristotle, Descartes accepts that the fundamental "stuff" in the universe is substance, which is not dependent on anything else: properties and events depend on substance, not the other way around.

Unlike Aristotle, who argues for innumerable different substances arranged into a hierarchical classification, Descartes says that there are only three types of substance:

  1. God is the substance which depends "on no other thing whatsoever"
  2. corporeal substance is what all material things are made of (by God)
  3. mind is "thinking substance"

Descartes' view separates mind from corporeal substance. This is in line with his writings in the second Meditation, where he says that it even though all material things perceived through his senses may be illusions, the fact that he can think is proof of his (mind's) existence.

Descartes agrees with Aristotle that substances have properties, but goes further in saying that each substance (God/corporeal/mind) has "one principal property which constitutes its nature and essence". And it is this principal property is responsible for all the other properties.

In the case of corporeal substance, the principal property is extension, or the physical space which it occupies. Other properties (e.g. length, height, movement) are dependent on this principal property - they couldn't exist without it.

For mind, the principal property is thought. All other aspects of mind - emotion, imagination, intelligence are dependent on thought.

Descartes thinks that all corporeal substance is made up of small parts of the same "stuff" which can move. Objects that we see are made up of stuff and so are divisible into smaller parts, and occupy physical space (atomism). On the other hand, mind appears to be indivisible, and occupies no physical space.

Aspects of corporeal substance such as colour, hardness, and weight are not properties of the substance: rather, they are experiences (i.e. thoughts) that result in us when we interact with the substance. Note that the experience I have of the colour of an object is distinct from the experience that you have of the colour of that same object.

A human being is a composite of mind and substance, but in Descartes' view, there is no dependence of one on the other: they are associated with one another, but there is no requirement that a mind has a body in order to exist.

The passage concludes with Descartes saying that "the only principals which I accept or require...are those of geometry and pure mathematics". He seems to be saying here that all you need to understand in order to be able to explain the material world is the way that maths and geometry works. This explains how all of the bits of stuff are moving around and what happens when they bump into each other.

Descartes' view is not so "common-sense" as Aristotle, but has resonances with what we believe now about the way that the universe is made - built up of atoms etc..

Descartes' ideas present a problem: how do mind and physical body interact with each other? We know that physical substance can affect mind: when you burn your hand, you feel pain and distress; when you want to scratch your nose, your arm and hand move. Scientific theory would say that all physical events have other physical events as their cause.

Perhaps Descartes is limited by the scientific world-view of his time, and has to invent the idea of a mind because he doesn't know about neuroscience etc., which might nowadays claim to be able to explain "mind" in purely mechanical terms of chemical reactions going on in the brain.

When I look at a material object, I am not aware of the table itself, just "how it appears to me" - the state of consciousness which the table provokes in me. The table may just be a hypothesis suggested by my mind to explain all the feelings that it invokes in me.

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