Descartes: Res Cogitans and the Mechanical Universe

Descartes: *Res Cogitans* and Mechanism

The First Principle: *Cogito Ergo Sum*

Applying the first rule of his method—to accept only clear and distinct ideas—Descartes concludes that the first glimmer of truth is "I think." From this, he raises the fundamental question: "What am I?"

Descartes' Conception of Substance

To explain the essence of the self, we must understand these concepts:

• Substance: That which needs nothing else to exist (only applicable absolutely to God).
• Mode: That which needs a substance to exist.
• Attribute: The essential characteristic of a substance.

Descartes distinguishes three types of substances:

1. The self, whose attribute is thinking.
2. God, whose attribute is perfection.
3. The world, whose attribute is extension.

*Res Cogitans*: The Thinking Thing

Descartes' second truth refers to the essence of the self. He replaces Platonic dualism, asserting: "I am my soul, a thinking thing (*Res Cogitans*) entirely distinct from the body." The body's existence is undeniable, but thought itself is certain. The self is a substance whose essence is thinking.

The Problem of the Interaction Between *Res Cogitans* and *Res Extensa*

This radical separation between thought and extension raises the question of humanity's place in a mechanistic universe.

*Res Extensa*: The Extended Thing

Descartes names the third substance *Res Extensa*, characterized by geometrical extension.

Mechanism and the Material World

Descartes' mechanistic world view portrays physical reality as a system of bodies in motion. Mechanism reduces material reality, excluding secondary qualities because they cannot be mathematized.

Mechanism and Living Beings

Descartes views animals as complex machines. Inspired by Harvey's discovery of blood circulation, he explains bodily functions using the concept of "animal spirits." He uses this to explain life in animals without resorting to a vegetative or sensitive soul.

Human Beings: A Unique Case

For Descartes, humans possess a spiritual and immortal soul, completely separate from the animal world. However, he acknowledges an interaction, possibly through the pineal gland.

The Cartesian Universe: A Divided Reality

The Cartesian universe is divided into two parallel worlds (*Res Cogitans* and *Res Extensa*), leaving humanity's place unresolved. This lack of communication between substances is a problem addressed by later philosophers like Spinoza and Leibniz.