Descartes and Rationalism: A Deep Dive

Posted on Nov 15, 2024 in Philosophy and ethics

Descartes and Rationalism

Rationalism, a philosophical current originating in the 17th century with René Descartes, was further developed by thinkers like Leibniz and Spinoza. Its philosophical context arises from two key factors:

  1. The crisis of scholasticism (starting in the 14th century with William of Ockham and Nominalism), where the domains of faith and reason began to separate, leading philosophy to focus on tangible realities.
  2. Renaissance humanism, which revived the Greek tradition, placing man at the center of the universe and emphasizing human dignity and innate abilities. In contrast to medieval theocentrism, the Renaissance was anthropocentric.

These changes gave rise to Rationalism, which is characterized by:

  • Absolute confidence in human reason: A belief in reason’s ability to discover truths independently, without relying on senses.
  • Unitary conception of reason: The structure of reason is singular and applicable to various contents.
  • Innatism of ideas: The ultimate justification for ideas lies within reason itself. While some ideas originate from sensory experience, the first principles of knowledge are inherent and transcend the senses.
  • Emphasis on method: Given reason’s singularity, a structured, general procedure is essential for acquiring knowledge.

The Cartesian Method

Descartes’ method, outlined in his 1637 Discourse on Method, provides a reliable path to avoid errors in knowledge and establish fundamental truths. It comprises four rules:

  1. Evidence: Only accept truths that are clear and distinct.
  2. Analysis: Decompose complex issues into simpler, indivisible elements (simple natures) for intuitive understanding.
  3. Synthesis: Deductively link simple natures to form complex ideas, ensuring certainty throughout the process.
  4. Review and Enumeration: Mentally review the entire deductive chain to confirm the validity of the demonstration.

This method closely resembles the deductive method used in mathematics.

Approaches and Levels of Doubt

Descartes employed methodical doubt to identify and discard uncertain knowledge, aiming to uncover a core of absolute truth. He proposed three levels of doubt:

  1. Senses: Senses can deceive, providing false information about the world. If they err occasionally, there’s no guarantee they won’t always do so.
  2. Dream vs. Reality: The inability to distinguish dreams from waking life introduces radical doubt, as seemingly obvious truths can be false upon awakening.
  3. Evil Genius: Even mathematical principles could be deceptive if an omnipotent, malicious entity constantly manipulates our perceptions.
The Discovery of Self and the Criterion of Truth

Descartes’ famous “I think, therefore I am” establishes an undeniable truth. Doubting implies thinking, and thought necessitates existence. This discovery is crucial for two reasons:

  1. It distinguishes between mind (thinking substance) and body (matter).
  2. It establishes the existence of the thinker as the first and most certain truth, serving as the prototype for all other truths.

From this principle, Descartes derives his criterion of truth.

The Ideas of Self

Descartes categorizes ideas within thought into three types:

  1. Adventitious Ideas: Ideas seemingly derived from external experience through the senses.
  2. Factitious Ideas: Ideas constructed by the mind by combining adventitious ideas.
  3. Innate Ideas: Ideas inherent to thought itself, not originating from experience or combination. These are crucial for rationalism, forming the basis for a system of truth.

The Existence of God and the World

Descartes demonstrates the existence of the world based on the existence of God, using two arguments:

  1. The idea of infinity, which is innate and identified with God, possesses more reality than the idea of the finite.
  2. The ontological argument.

The existence of the physical world is then inferred from God’s goodness and truth, as a benevolent God wouldn’t deceive us about external reality.

The Three Substances

Descartes identifies three substances:

  1. God: A substance that exists independently.
  2. Soul (Thought): A substance distinct from the body.
  3. World (Extension/Matter): A substance behaving like a mechanism, driven by necessity.

While the soul and body are distinct, the soul possesses will and freedom.