Descartes’ Rationalism: Method, Doubt, and the External World

Posted on Nov 17, 2024 in Philosophy and ethics

Descartes

I. Introduction to Descartes

For Descartes, a rationalist, reason is paramount. He distrusts faith, grounding his philosophy in reason and doubting the senses. He posits that a priori knowledge, derived from reason itself, reflects reality. Knowing reason’s structure means knowing reality. Descartes believes God used mathematics to create the world, dismissing experience. He focuses on:

  1. Method: Seeking foundations to prevent reason from erring, using a mathematical approach.
  2. Mechanism: Rejecting purpose, focusing on efficient causes. Bodies are reduced to mass points in infinite space, disregarding essences.
  3. Subjectivism: The subject takes precedence over the object. We must prove the external world’s existence and determine if it aligns with our perceptions. We know the image of objects, not the objects themselves.

II. Method

Descartes develops rules to avoid errors in reasoning:

  1. Reason’s Functions: Intuition (immediate intellectual grasp of simple things) and deduction (deriving complex objects from premises). Correct intuition is analysis; correct inference is synthesis.
  2. Rules for Intuition: Decompose the compound into simple, clear, and distinct elements. Focus on what you see, avoid haste or excessive caution. Truth is grasped through a system where parts are known from the whole.
  3. Rules for Deduction: Each step must logically follow the previous one. Review steps to avoid errors.

III. Applying the Method to Philosophy

  1. Methodical Doubt: Doubt everything that can be doubted to find indubitable truth. Doubt the senses, the external world (psychological facts, dreams), and even mathematics (relativism, genius metaphor, psychologism). However, doubting itself is indubitable: “I think, therefore I am.”
  2. Synthesis: Working with thoughts (innate, adventitious, factitious ideas), Descartes seeks to prove the external world’s existence. The idea of a perfect, infinite God, innate within us, proves God’s existence. God guarantees the external world and mathematics. We know the world through reason, not the senses.

3. Characteristics of the External World

3.1. Extension = Matter

Space is always full of matter.

3.2. Problem of Atoms

Descartes argues against atoms, stating space is infinitely divisible.

3.3. Finitude of the World

The world is finite, unlike the infinite God.

3.4. Contingency

The world’s creation was contingent on God’s will.

3.5. Universe

Understand the universe through mathematics, focusing on causes and effects, not essences. The universe is a machine.

3.6. Mechanism

  • No freedom in nature; only the “self” has freedom.
  • No animal or plant life.

3.7. Mechanical Laws of the Universe

  • Principle of Inertia: No change of state without force.
  • Principle of Direction of Movement: All movement tends to a straight line.
  • Principle of Conservation of Movement: Movement is neither created nor destroyed.

3.8. Truths

God uses mathematics to create physical laws, which could have been different. God is above logic and mathematics.

IV. Man

  1. Anthropological Dualism: Only humans have a soul (“I”). The body and soul interact via the pineal gland. Passions are involuntary and explained by physics.
  2. Moral Philosophy
    • Reason must subdue passions.
    • Prudence is the ultimate virtue.
    • Follow likelihood when clarity is lacking.
    • Standards: Obey laws and traditions, be moderate, be resolute, and change yourself before changing the world.