Early Modern · 1596–1650
Descartes
Their big question
“How do I know that ANYTHING is real?”
René Descartes wanted certainty, so he tried doubting absolutely everything — his senses, his body, even math. But he realized one thing was impossible to doubt: that he was doubting, which means thinking, which means he must exist. ‘I think, therefore I am’ became his rock-solid starting point for rebuilding all of knowledge.
“I think, therefore I am.”
The big idea
Descartes used ‘methodical doubt’ — refusing to accept anything he could possibly doubt — to find one unshakable truth: ‘I think, therefore I am.’ From there he tried to rebuild knowledge using reason alone. He's the father of rationalism, the view that reason (not the senses) is the surest path to truth.
Why it matters
He launched modern philosophy and invented the coordinate system in math — the x–y ‘Cartesian’ graph you use in school is named after him. His method of starting from doubt and reasoning step by step shaped science and mathematics.
The big argument
Descartes split reality into two separate substances, mind and body, creating the famous ‘mind-body problem’: how can a non-physical mind control a physical body? Philosophers and scientists still argue about it.
In their own words
- “It is not enough to have a good mind; the main thing is to use it well.” — René Descartes
- “Doubt is the origin of wisdom.” — René Descartes
🤯 Fun fact
Descartes claimed he came up with his whole method after three vivid dreams in a single night.
Learn more
Portrait: Portrait of René Descartes, after Frans Hals. Public domain · via Wikimedia Commons.
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