How did Descartes try to build a complete system of knowledge from the cogito?

René Descartes sought to build a complete system of knowledge by using the cogito—the intuition that "I think, I am"—as an indubitable foundation after applying methodic doubt to all other beliefs.12

To move beyond the solipsism of his own existence, Descartes argued that any idea perceived as clear and distinct must be true, as the cogito itself is a clear and distinct idea that cannot be doubted. Using this criterion, he employed innate ideas to establish the existence of God through the ontological argument, which posits that a perfect being must necessarily exist.1

Descartes then reasoned that because God is perfect, He cannot be a deceiver. Consequently, God guarantees the truth of our clear and distinct perceptions, which allows us to trust in the existence of the material world and the reliability of our reasoning. This ambitious project aimed to provide metaphysical foundations for the mind, God, and the physical universe, though critics later identified a circularity in his logic known as the Cartesian Circle.1