Descartes: Rationalism, Method, and the Three Substances

René Descartes (1596-1650)

René Descartes (1596-1650) was a philosopher and mathematician. He was a key figure in the development of rationalism.

Descartes' Method

He devised a method that would allow progress with secure knowledge. This method is divided into four parts:

• Evidence: Do not accept anything that is not clearly evident to human reason.
• Analysis: Divide the problem into smaller parts and examine each one.
• Synthesis: Once you have the necessary elements, arrange them in an order, starting with the simplest and moving to the more complex.
• Enumeration: Review the process to ensure nothing has been omitted or done incorrectly.

The First Question and the First Truth

Descartes doubted all knowledge to arrive at a universal question. This doubt led him to the first undoubted truth: cogito, ergo sum (I think, therefore I exist). This is the first fundamental knowledge base across Cartesian philosophy.

The Three Substances

Using his method, Descartes identified three substances as comprising all of reality. These substances are: the thinking self, God, and the world.

The Thinking Self

Universal methodical doubt led to an undeniable truth: the existence of the thinking self, that is, a substance that thinks, a soul. Descartes concluded that he could doubt the existence of his body and the world around him because he received information through the senses, and the senses are unreliable. However, he could not doubt the existence of his thoughts, his ideas, etc.

The thinking self is an imperfect substance endowed with reason.

Descartes classifies the ideas of the thinking self as follows:

• Adventitious or acquired: These are ideas that come from outside, from sensory experience. They may be misconceptions.
• Factitious or artificial: These are ideas that we invent ourselves. For example, the idea of a mythical animal called a centaur.
• Innate or natural: These emerge from the faculty of thinking itself. These are ideas that our minds capture and necessarily accept without the ability to change them. For example, the idea of God.

God

Descartes believed that the thinking self is not perfect, but still possesses a sense of perfection. This innate idea of a perfect being is the idea of God.

God is a guarantee of knowledge. God is a substance with perfect reason.

The World

We have clear and distinct ideas of the extensive body (matter), separate from the mind. While the existence of the body can be doubted, the existence of matter (stuff) cannot. God created us rationally and cannot allow us to be deceived when we use our reason correctly. Therefore, the goodness of God guarantees the existence of matter.

Thus, finite and created substance exists: bodies.

Bodies are imperfect substances with primary and secondary qualities.

Freedom and Mechanism

Thanks to the thinking soul, we have freedom. However, our behavior can be seen as resembling a machine.

The body, as matter, is governed by mechanical laws. Mechanism stimulated the study of our body but also promoted a very respectful attitude towards nature.