Descartes’ “I Think, Therefore I Am”: Justification and Impact

Posted on Mar 6, 2025 in Philosophy and ethics

Descartes’ Methodological Doubt and “I Think, Therefore I Am”

Subject:

Reasons to justify methodological doubt and arrival at the first principle of Cartesian philosophy: “I think, therefore I am.”

Key Ideas:

  • The senses deceive us, so what we perceive through them is false.
  • Since we err, everything we had considered proven should be rejected.
  • Thoughts are presented to us both when awake and asleep, so our perceptions are no more real than illusions.
  • It is impossible to doubt everything, because the act of thinking implies existence: “I think, therefore I am.”
  • This statement is undeniable, making it the first principle of his philosophy.

Structure of the Argument:

  • Enumeration of reasons for doubting the truth of things:
    1. The senses deceive us, so we know they are unreliable.
    2. Because we err, everything previously proven should be questioned and rejected.
    3. As thoughts are presented to us both asleep and awake, we cannot distinguish reality from illusion.
  • Exception: An undeniable truth exists: the act of thinking, even about falsehood, cannot be false (“I think, therefore I am”).
  • Conclusion: Descartes adopts this statement as the first principle of his philosophy because of its irrefutable nature.

Explanation of the Ideas:

Descartes’s thought revolves around three main influences:

  1. Critical thinking of scholasticism, which he considered obsolete.
  2. Skeptical thought, which inspires his methodological doubt.
  3. The new science, which he takes as a model of thought.

Descartes tried to solve the problems posed by Scholasticism (its inability to explain new advances in science and its reliance on authority) through the search for a new criterion of truth and a new method.

This new criterion of truth stems from methodological doubt. This critical attitude involves doubting the veracity of everything that does not appear clearly and distinctly true. Descartes sought to eliminate all false beliefs and opinions and start again from new, fundamental principles.

This doubt arises from three basic postulates:

  1. The senses deceive us, because no one assures us that things are how we perceive them.
  2. The difficulty of distinguishing between wakefulness and sleep, which allows us to question whether the material world we perceive is real.
  3. The evil genius hypothesis: instead of God, there is an evil entity, infinitely powerful and intelligent, whose interest is to confuse and deceive, including mathematical truths.

Thus, Descartes initially doubts everything, including mathematical truths, the existence of God, and his veracity. Despite being so radical, this doubt has a purpose: to get rid of prejudices and move away from what the senses dictate.

But at this point, Descartes realizes he cannot doubt the existence of the doubter. Because everything can be doubted, the act of doubting itself exists. If one doubts, one thinks; therefore, if one thinks, one exists (“Cogito ergo sum” – I think, therefore I am).

From this first undeniable truth, he reconstructs knowledge, justifying aspects previously questioned: his own existence, his nature (a thinking thing, res cogitans), the existence of God (assuming that we have the idea of perfection, but we are not perfect, there must be a perfect being who placed it within us), rejection of the evil genius (God exists and deception is an imperfection; since God is perfect, God is truthful), and the existence of the external world (as God is perfect and truthful, he does not deceive us into believing that the world exists – res extensa).

The reason for proposing a method is to use reason properly and thus attain true knowledge. This method has two kinds of knowledge: intuition and deduction. It also presents a set of rules to ensure the advancement of knowledge: rational evidence approach (methodological doubt), analysis, synthesis, and enumeration (review).