The philosopher René Descartes (1595-1650) was fed up with his education.
All the philosophers and schools of thought he studied claimed that their arguments were true.
He did not know whom to believe and wasn’t particularly happy about being another brick in the wall.
So he decided to set out a rigorous method with clear criteria to find out a solid foundation to acquire certainty.
The Method of Doubt
Descartes decided to systematically doubt all his beliefs.
Any proposition or source of knowledge that he could slightly doubt, he would consider as either false or an unreliable source of knowledge.
His method was intended as a way to reach some sort of truth, and not because he wanted to be a skeptic for the fun of it.
And so Descartes proceeded to doubt:
a) His senses because they’re deceiving.
b) His dreams, because sometimes he wasn’t sure whether or not he was awake or asleep.
c) Math because how can he be certain that 1+1=2?
d) Whether or not God exists, because he had no definitive proof.
The Evil Genius
Descartes opted for the worst-case scenario.
He assumed that he was being deceived by an evil genius.
Much like Truman and Christoph from The Truman Show, Descartes assumed that he couldn’t trust his experience of the world because nothing guaranteed that it was trustworthy.
But given the worst-case scenario, he was sure of one thing: that even if he was being manipulated by an evil demon, he had to exist in the first place to be deceived!
It was this realization that got Descartes to affirm that the unshakeable foundation, the immediate self-evident truth he was aware of was that he existed as a thinking thing.