Exploring Cartesian Dualism

René Descartes is one of the most influential philosophers of all time, and his ‘mind-body dualism’ thesis (also known as Cartesian Dualism) is perhaps one of his most popular legacies. In this thesis, he argues that the nature of the mind as a thinking, non-physical thing, is completely different from that of the body, as a non-thinking, physical thing. Therefore, as they are ‘really distinct’, each of these can exist independently of the other.

Understanding what ‘real distinction’ means

A substance can be comprehended to exist alone without requiring any other substance for its existence. One example of this is rocks. Rocks do not require the existence of other things to exist. So, it follows from this that God could create a world containing just rocks, argued Descartes. This shows that substance is ‘really distinct’ from everything except for God.

Hence, the mind-body dualism thesis implies that mind and body are really distinct in the sense that each could exist all by itself, without any other body, including each other, if God chose to do it. It should be noted here that just because substances could exist independent, does not mean that they actually do.

Importance of real distinction

Descartes put forward two reasons in support of mind-body dualism. The first is religious in nature as his thesis provides a rational basis for the soul’s immortality (for him, mind and soul were synonymous). The second reason is a scientific one, as it gives Descartes a way to make his own version of a new mechanistic physics in the absolute absence of mentality from the nature of physical things.

Religious motivation

In Meditations of First Philosophy, Descartes clarifies that the reason he is highlighting the real distinction between body and mind is to rebut those unbelieving, atheistic people who demand a mathematical proof for believing in the soul’s immortality.

Scientific motivation

The scientific motive for Descartes’ mind-body dualism is rooted in his desire to replace the final-causal explanations in physics with mechanistic explanations based on the model of geometry.

The two versions of the real distinction argument

Descartes has presented two different versions of the same argument, of which the fundamental premise of each is identical, claiming that the natures of mind and body are completely different from each other.

The first version

This excerpt has been taken from Descartes’ Sixth Meditation –

On the one hand, I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing [that is, a mind], and on the other hand, I have a distinct idea of body, in so far as this is simply an extended, non-thinking thing. And accordingly, it is certain that I am really distinct from my body, and can exist without it.

This argument can work for any ‘I’ or ‘mind’, since for Descartes, both were synonymous. So, to generalize the argument, ‘I’ can be substituted with ‘mind’ in the required places-

1. I have a clear and distinct idea of the mind as a thinking, non-extended thing.
2. I have a clear and distinct idea of the body as an extended, non-thinking thing.
3. Therefore, the mind is really distinct from the body and can exist without it.

Descartes claims this intellectual perception to be ‘clear and distinct’, and hence guarantees the truth of his argument. He elucidates what he implies with ‘clear and distinct’ in part 1 of Principles of Philosophy. An idea is said to be distinct and clear when it is in sharp intellectual focus and all other ideas that don’t belong to it are excluded from it.

Descartes claims that in both his premises (1 and 2), all other ideas that do not belong to mind or body are excluded, including each other. This is why Descartes clearly and distinctly understands both of these entities separately, and capable of existing all by themselves.

In the Fourth Meditation, Descartes greatly emphasizes the guarantee of the truth of that which is clearly and distinctly understood. This guarantee is dependent on the claim that God exists and s/he cannot be a deceiver. As per him, anything that goes against this belief has to be false. Also, since God is the sole author of all the clear and distinct ideas, faith in the non-deceiving nature of God is the only way of ascertaining their truth.

Descartes gives the following line of reasoning to explain how he makes a valid inference from his distinct understanding of mind and body as two completely different things to their independent existence.

1. The idea of contingent existence is contained within all the ideas of finite things.
2. Descartes is picturing body and mind as existing independently without any other object.
3. There is no doubt about the possibility of (2) for him.
4. Since God is omnipotent, he could bring about (2) should s/he wish to.
5. Hence, God’s omnipotence makes Descartes’ experienced logical possibility a metaphysical possibility.

As God’s will is all that mind and body require to exist separately, they really are two distinct substances.

The second version

This excerpt has been taken from Descartes’ Sixth Meditation –

There is a great difference between the mind and the body, in as much as the body is by its very nature always divisible, while the mind is utterly indivisible. For when I consider the mind, or myself insofar as I am merely a thinking thing, I am unable to distinguish any parts within myself; I understand myself to be something quite single and complete…by contrast, there is no corporeal or extended thing that I can think of which in my thought I cannot easily divide into parts; and this very fact makes me understand that it is divisible. This one argument would be enough to show me that the mind is completely distinct from the body.

This argument can be simplified into the following one, with the replacement of ‘mind’ for ‘I’ as before:

1. I understand the mind to be indivisible by its very nature.
2. I understand the body to be divisible by its very nature.
3. Therefore, the mind is completely different from the body.

Here, he does not assert a clear and distinct understanding of the natures of the two as being completely different but instead uses one particular property — divisibility, to make his point.

These ‘objects’ are said to be in possession of this property (divisibility) by their very ‘nature’. Hence, extension constitutes the nature/essence of bodily objects, while thinking constitutes the nature/essence of mental things.

Descartes gives the following reasoning in support of his argument–

1. It can be clearly observed that bodies are divisible. For example, one piece of chalk can be broken into multiple pieces.
2. Descartes believed his mind to be indivisible, because ‘mind’ is ‘I’, and upon its division, there would be two or more ‘I’s’ or selves, which would be absurd.
3. Therefore, the body is essentially divisible while the mind is essentially indivisible.

Descartes was required to highlight the complete diversity between mind and body to claim that his conception of each is completely independent of one another. He reaches this conclusion after having proved the mind’s and body’s essential properties as completely contradictory.

Similar to the first version of the same argument, here too mind and body have been portrayed as complete opposites. This naturally implies that–

1. A divisible body can be understood without an indivisible mind and vice-versa.
2. Each can be conceived as existing all by itself as they are both really distinct substances.

Sources — Internet Encyclopedia of Philosophy and The Philosophical Writings of René Descartes

Also read — Cartesian Dualism and the Mind-Body Problem