Who famously coined the phrase "I think, therefore I am"?

Descartes famously declared “I think, therefore I am” (French: “Je pense, donc je suis”; Latin: “Cogito, ergo sum”) as the indubitable foundation of knowledge. Using methodic doubt, he questioned everything—senses, beliefs, even mathematics—until he found one certainty: if he is doubting or thinking, he must exist as a thinking being. This idea anchors modern philosophy and rationalism. Context: Descartes published the line in Discourse on the Method (1637), later phrased in Latin in Principles of Philosophy (1644). It set a new standard for certainty based on reason, not authority. Memory tip: D is for Descartes and Doubt—by doubting, he discovered the one thing he couldn’t doubt: his own thinking existence. Aristotle and Plato were ancient Greeks; Shakespeare was a playwright, not a philosopher of doubt.