Which French philosopher famously declared 'I think, therefore I am'?

Which French philosopher famously declared “I think, therefore I am”? René Descartes is the philosopher associated with the statement, known in Latin as cogito, ergo sum. It expresses his attempt to find one certainty that survives radical doubt.

Descartes reasoned that sensory experiences and even apparently certain beliefs might be mistaken. Yet the act of doubting is itself a form of thinking. If thinking is occurring, there must be a thinking subject—or, at minimum, an existent mind engaged in that thought. He used this insight as a foundation for rebuilding knowledge.

The familiar wording first appeared in French, “Je pense, donc je suis,” in his 1637 Discourse on the Method. A related formulation appears in his 1641 Meditations on First Philosophy, while the recognizable Latin phrase appears in his 1644 Principles of Philosophy. Thus, the popular quotation is associated with Descartes but was not originally introduced in the famous Latin form in 1637.

The statement does not mean that every belief is automatically true. It claims that the occurrence of thought provides immediate certainty of the thinker’s existence. Earlier thinkers, including Augustine, expressed similar ideas, but Descartes made the cogito central to modern philosophical method.