Who is credited with saying 'I think, therefore I am'?

The profound philosophical declaration, "I think, therefore I am," is famously attributed to the 17th-century French philosopher René Descartes. This statement, originally penned in French as "je pense, donc je suis" in his 1637 work *Discourse on the Method*, and later in Latin as "Cogito, ergo sum," serves as the foundational principle of his philosophy. It emerged from Descartes' radical method of doubt, where he systematically questioned the truth of all his beliefs to find something undeniably certain.

Descartes embarked on this intellectual journey by doubting everything, including the reliability of his senses and the existence of the external world, even considering the possibility of an "evil demon" deceiving him. However, he realized that even if he were being deceived, the very act of doubting or thinking proved that he, as a thinking entity, must exist. It is impossible to doubt one's own existence while one is doubting, because the act of doubting is a form of thinking, and thinking requires a thinker. Thus, the statement became his first irrefutable truth, a self-evident proposition that could not be false when conceived in his mind.

This seemingly simple phrase profoundly altered the course of Western philosophy. By establishing the certainty of individual consciousness as a starting point, Descartes provided a new foundation (Review) for knowledge based on reason and introspection, rather than solely on external authority or sensory experience. The "Cogito" became a cornerstone for modern philosophy, influencing later movements and emphasizing the crucial role of the individual mind in understanding reality.