Descartes and Rationalism

Descartes founded the rationalist tradition — the view that reason rather than sensory experience is the primary source of knowledge. Your senses can be fooled by illusions, dreams, and deception. But mathematical and logical truths seem immune to these errors.

Two plus three equals five regardless of what your senses report. The internal angles of a triangle sum to 180 degrees whether or not any physical triangle exists. Descartes argued that these necessary truths demonstrate the mind's ability to access reality directly through reason without relying on unreliable sensory data.

Empiricists like John Locke and David Hume pushed back, arguing that even mathematical knowledge ultimately derives from experience.