René Descartes (1596-1650)

French philosopher and mathematician. Pioneered systematic doubt and deductive reasoning. Famous for the formulation "I think, therefore I am" (Cogito, ergo sum). Where Bacon emphasized observation, Descartes emphasized rational deduction. The two approaches together defined modern scientific method.

Testable pattern: The Regents often presents a quote from a Scientific Revolution thinker and asks for identification or for the significance of the work. Recognition cues: Copernicus and heliocentrism, Galileo and the telescope or the trial, Newton and universal laws or gravity, Bacon and the inductive method, Descartes and rational doubt.