Cogito Ergo Sum (I Think, Therefore I Am)

The foundational certainty that one's own existence is proven by the very act of thinking or doubting, serving as the first principle from which all other knowledge is built.

The cogito emerges as the first principle of philosophy, establishing the self as a thinking thing and providing a starting point for further knowledge.

The first principle of Descartes' philosophy: the certainty of his own existence as a thinking thing, immune to the most extravagant skeptical doubts.

The mind, in doubting all things, discovers its own existence as the first certainty, establishing the foundation for all subsequent knowledge.

In the Second Meditation, the mind finds that it must exist even while doubting all else, establishing the first certainty.