Descartes’ Method: Rules, Doubt, and the Second Truth

Posted on Mar 7, 2025 in Philosophy and ethics

The aim of Descartes’ philosophical project is to define good sense or reason as the ability to judge and distinguish the true from the false. Possessing reason is not enough; the main thing is to apply it well. A method is needed to guide the proper use of reason.

Influence of Logic and Mathematics

The Cartesian method is influenced by logic and mathematics. Logic highlights deductive power but is criticized for its inability to provide new knowledge. Mathematics provides the ability to construct knowledge from obvious axioms. The method is mainly mathematical, combining intuition of axioms and deduction of new knowledge from them.

Structure of Reason and Method

Intuition and deduction are key. Intuition grasps self-evident truths, while deduction derives new knowledge from these truths.

Rules of the Method

First Rule: Evidence

Admit nothing as true unless it is clearly known to be such. Avoid precipitation and prevention, and base judgments solely on what is presented clearly and distinctly to the mind, leaving no reason to doubt it. This is the criterion of truth: only the obvious, immediately clear and distinct is real. Obvious ideas can only be intuited, not deduced. Clear ideas are simple ideas. Clarity means the perception of the idea is presented immediately. Distinction means the idea is precise and unmistakable from another idea. The idea of a point is an example of distinction.

Second Rule: Analysis

Divide each difficulty into as many parts as possible and necessary to resolve them more easily. This process of analysis is to be followed by reason to access simple ideas from complex ones.

Third Rule: Synthesis

Direct thoughts in order, beginning with the simplest and most easily knowable objects, to rise gradually to knowledge of the most complex. These two rules govern the operation of deduction.

Fourth Rule: Enumeration

Make counts as complex and revisions so broad that they ensure nothing is missed. This represents verification of the analysis and synthesis.

Cartesian Doubt

Levels of Doubt

  1. First Level: The senses deceive us. Since our senses sometimes lead to error, assume that anything shown to us might be a deception.
  2. Second Level: Mathematics can be wrong. Since some men err in thinking and acting in paralogisms, consider that I, as another, was subject to error, rejecting as false all reasons demonstrated by both logical and mathematical knowledge because there are paralogisms.
  3. Third Level: Indistinguishability between sleep and wakefulness.
  4. Fourth Level: The evil genius hypothesis.

The Second Truth: God

Arguments for God’s Existence

  1. First Causal Argument: Descartes has the idea of a perfect being. It can only be caused by a Perfect Being. The self is not perfect, so the idea of God may not be artificial. The idea of perfection is innate, and only God can be the cause of that idea.
  2. Second Causal Argument: Leads to the question of whether the thinking self could be the cause of itself, but since it is an imperfect being, it cannot be the cause of a perfect being. Only a perfect being can be a cause of itself.
  3. Third Argument (Ontological): The ego has the idea of a perfect being. When analyzed, it must be realized that containing all the traits of perfection must also contain existence because otherwise, this idea would represent a being that contains all perfections except existence, and therefore would not be perfect.