Descartes' Cogito Ergo Sum and the Problem of Solipsism

Cogito, Ergo Sum: The First Certainty

"I think, therefore I am." With this famous phrase, Cogito, ergo sum, one of the most renowned in the history of philosophy, Descartes fundamentally asserts two things. First, it is the first truly indubitable and certain truth. After applying his method of doubt and setting aside the entire edifice of knowledge, Descartes realized that the thinking subject, even if mistaken in their thoughts, must necessarily exist in order to think. This truth, "I think, therefore I am," is so firm and certain that it cannot be doubted. Secondly, this phrase implies that a human is essentially a substance whose nature is to think; for Descartes, being and thinking are identical.

After attempting to doubt everything to find a truth safe from uncertainty and error, Descartes had two simultaneous intuitions: the fact of his thought and the fact of his own existence. He could doubt everything else, but not the act of thinking itself and, consequently, not his own existence.

The Danger of Cartesian Solipsism

This realization solves one part of the problem—the certainty of his own existence—but what about everything else? Does the external world exist, or is it a mirage? At this point, a danger arises: the problem of being trapped alone in one's own mind, known as Cartesian solipsism.

Proving God to Escape Solipsism

Up to this point, Descartes' philosophy is considered brilliant. However, his subsequent move to establish an ontology is often criticized. He attempts to solve the problem of solipsism by resorting to the goodness of God as a guarantor for the reliability of his perceptions. Where he once posited an evil genius or a deceiving God, he now must rely on a benevolent God to escape the metaphysical solipsism he reached with the intuition of his Cogito. Therefore, the next step in his philosophy is to demonstrate the existence of God.

The Ontological and Cosmological Arguments

To do this, he uses several arguments, which are not entirely original. He largely restates the ontological argument of St. Anselm and versions of the Aristotelian cosmological proofs for a prime mover and first cause, previously used by Thomas Aquinas, with minor variations. In essence, he argues for God's existence either from the definition of God as a perfect being (who cannot lack the perfection of existence) or from the contingency of all other beings, which necessitates a non-contingent creator. Once God's existence and goodness are established, Descartes believes he has a fundamental piece of his philosophical puzzle.

A Cartesian Syllogism for Truth

These assumptions can be developed into a syllogism, following four steps:

1. God is a perfect being.
2. A perfect being would not deceive.
3. Our clear and distinct ideas are innate and come from God.
4. Therefore, any idea that is clear and distinct must be true, as it is guaranteed by God.