Descartes' Metaphysics: Thinking, God, and the World

The Three Substances in Descartes' Metaphysics

The Thinking Substance (Cogito)

In Descartes' philosophy, the starting point is the undeniable existence of the thinking self. He argues that even if one doubts everything, the very act of doubting proves that there is a thinking entity. This is the famous "Cogito, ergo sum" - "I think, therefore I am." The cogito, or the thinking self, is characterized by thoughts, ideas, and subjective representations. However, Descartes acknowledges that these internal experiences might not accurately reflect the external world. He grapples with the challenge of determining whether his ideas are mere imaginings or objective truths.

Descartes classifies ideas into three categories:

• Adventitious Ideas: These are images acquired from external sources through sensory experience. They represent the perceived world.
• Factitious Ideas: These are artificial ideas, arbitrarily invented by the imagination.
• Innate Ideas: These ideas emerge from the inherent capacity to think. They are not derived from experience but are inherent to the mind itself.

God as the Bridge to Reality

Descartes recognizes that the thinking self is imperfect. However, he posits that the very awareness of imperfection implies the existence of a concept of perfection. He identifies this perfect being as God. Since imperfect beings cannot generate the idea of perfection independently, Descartes concludes that a divine reality must have implanted this idea in our minds. This innate idea of God allows the individual to transcend their subjective experience and connect with an external reality.

For Descartes, God serves as the guarantor of truth and knowledge. He argues that God, being perfect, would not deceive us. Therefore, the clear and distinct ideas we perceive, such as those found in mathematics and the fundamental principles of nature, must be true. He uses the example of a triangle, whose properties are inherent to its definition, to illustrate how God's existence is similarly inherent to His essence. God is the only being in whom essence and existence are inseparable.

The World as Extended Substance

Descartes' method leads him to identify a first substance, the thinking substance, and a second substance, God, who is perfect. Our reason, the thinking self, is aware of the difference between reason and the idea of the body. The body is extensive, meaning it occupies space, and is therefore subject to doubt. Besides the thinking substance, Descartes proposes another type of imperfect and finite substance called the body. The fundamental quality of the body is extension. This is the third substance in Descartes' metaphysics: matter.

All beings, according to Descartes, have a body composed of articulated parts capable of movement. The thinking self and the body belong to different orders. This raises the question: How do they interact? How does the thinking self command the body to move?

Descartes' answer lies in the pineal gland, located in the center of the brain. He believed that the soul resided in the pineal gland and, from there, connected with the body, initiating movement. This explanation reflects Descartes' attempt to reconcile his metaphysical dualism with a mechanistic view of the world, similar to Platonic dualism.