Descartes’ Method and the Search for Truth
3.1 The Four Rules
In the second part of his discourse, Descartes summarizes his analysis and reflections on the mathematical method and its philosophical application. Seeking a universal geometric method, he proposes four simple rules applicable to any science:
- Evidence: Accept only what is evident. Avoid both precipitation (accepting the unclear) and prevention (rejecting the clear). Clarity and distinction are the hallmarks of evidence.
- Analysis: Divide problems into simpler, clearer ideas.
- Synthesis: Deduce from simple ideas to more complex knowledge.
- Enumeration: Review thoroughly to ensure nothing is omitted.
These rules align with the mind’s two modes of knowing: intuition (grasping clear ideas) and deduction (extending evidence).
3.2 Methodical Doubt
To find indubitable truth, Descartes employs methodical doubt, questioning everything initially considered true. Three reasons drive this doubt:
- Unreliability of the Senses: Senses can deceive, so their knowledge is only probable, not certain.
- The Dream Hypothesis: Inability to distinguish waking from dreaming casts doubt on perceived reality.
- The Evil Genius Hypothesis: A hypothetical evil genius could deceive us even about mathematical truths.
a) Doubts about the Reliability of the Senses
Sensory illusions and hallucinations demonstrate that sensory knowledge is not always reliable. This doubt extends to the existence of our own bodies and the material world.
b) The Difficulty of Distinguishing Waking from Sleep
Vivid dreams can feel real, making it difficult to determine if we are awake or dreaming. This further undermines the certainty of the external world.
c) The Evil Genius Hypothesis
Even mathematical truths, seemingly certain, could be illusions created by an evil genius. This radical doubt challenges the foundation of all knowledge.
4. The Formulation and Justification of the Criterion of Truth
4.1 The Cogito: First Truth and Certainty Criterion
Descartes’ doubt leads to the first certainty: the existence of the thinking self (“I think, therefore I am” or cogito, ergo sum). Doubting itself proves the existence of the doubter. This truth, known by intuition, is clear and distinct. The cogito serves as the model for all truth.
5. Cartesian Concept of Ideas and Types
Descartes’ theory of ideas addresses the problem of proving the existence of the external world based on the existence of thought. He distinguishes three types of ideas:
- Adventitious
- Factitious
- Innate
Unlike previous philosophies, Descartes views ideas as direct objects of thought, not intermediaries. The existence of an idea doesn’t guarantee the existence of a corresponding external reality.