Descartes' Substance Theory: Mind, Body, and God

Descartes' Theory of Substances

The theory of the terms of commonality is the weakest part of Cartesian theory. The Cartesian doctrine of reality is based on the cogito, from which the self is sensed as a substance whose whole essence is to think. Descartes defines substances *a priori* under existing concrete entities, but one that does not need anything else besides itself. He distinguishes three types:

• Res Cogitans: The human being is conceived as a thinking substance; its body does not need thought to exist.
• Res Infinita: The thinking being is imperfect, so it needs a perfect being (God).
• Res Extensa: The thinking being has a body, just like everything else.

Descartes' concept of the thinking substance assumes that the only thing beyond doubt is the existence of thought. Thought is a substance that exists independently of the body; the mind and body are two different things.

The Problem of Interaction

Descartes defends the freedom of man with respect to the mechanical system that governs the universe. Furthermore, the independence of the substances poses a problem common to the entire rationalist movement: the communication of substances. While body and soul are two separate substances, both are united by the same self. To establish this unity, the philosopher uses the pineal gland. Through this gland, unity is achieved.

God and the Corporeal World

God, the infinite substance, is the result of imperfections inherent in the thinking being, whose existence is already secure. The *res cogitans*, as a finite being, is conceived as limited. Compared with the infinite, it is evident that the thinking being is handled by the concept of infinity; therefore, God exists. Descartes also uses the ontological argument to prove God's existence.

To explain the workings of the corporeal world, Descartes makes an analogy to the mechanism of a machine; it comes down to matter and motion. To explain the origin of movement, he denies gravitational force. From this idea, he deduces *a priori* the three laws of nature:

1. Principle of Inertia: Everything remains in the state in which it is.
2. Law of Nature: Every body tends to move in a straight line.
3. Law of Conservation of Mechanical Motion: This allows him to reject the vegetative and sensitive soul, thus designing a deductive method whose creator is God.

Descartes dispenses with experience and goes from causes to their effects: the physical world is a series of ordinances based on the first cause. For this, he relies on the goodness and infinity of God.

Conclusion

In conclusion, Descartes posits three ideas that we conceive clearly and distinctly: the soul, God, and matter.