Rene Descartes

Rene Descartes (1596-1650) began the modern philosophical project by doubting everything it was possible to doubt — and found that the one thing he could not doubt was the act of doubting itself. "Cogito, ergo sum" (I think, therefore I am) from his Meditations on First Philosophy (1641) is the most famous sentence in philosophy and the bedrock of the modern rational subject on which all subsequent Western thought is built. He proposed the mind-body dualism that still haunts philosophy of mind today, introduced the systematic scientific method in his Discourse on Method (1637), and co-invented analytic geometry — the Cartesian coordinate system that became the mathematical language of physics. Modern science rejected his theory of the pineal gland as the seat of the soul, but built much of its methodological infrastructure on his approach to systematic doubt.