René Descartes was an extremely influential man from the seventeenth century who touched nearly every discipline of knowledge.  Known as the father of modern psychology, he reinstated faith in knowledge by making a practice of doubting everything.  One of his most famous contributions was the Method of Doubt, which was a way to discover personal beliefs.

In this practice, he first takes away every piece of certainty that he previously held.   Then he analyzes everything with a critical eye before either discarding it or adding it to the knowledge that he is certain is true.  Thus, he has a base of beliefs that he feels confident standing on. This led him to one of his most well-known quotes made about the only thing he could really be certain of for a long time:

“I am thinking, therefore I exist.”

After he took every meaningful certainty away, he then reasoned ways to bring them back.  He eventually came to the conclusion that God exists, because “a lesser cannot give rise to a greater.” By this he means that, because he imagined an omnipotent, infinite being although he had never been or seen those things, God must exist, God must be omnipotent and benevolent, and God must have given me this idea of him as a “mark of the maker.”

He reasoned further that God essentially gave the field of science to observe the material world, and that if there were enough evidence to support a scientific belief, the belief couldn’t be wrong because the benevolent God wouldn’t let it be so.  Descartes also believed that anyone who thought long enough and who listened to his logic must believe as he did.  Everyone would come to the same conclusion if they were a skeptic or intellectual.

This allowed him to discover a world where mathematical physics is possible. Though his ideas of physics were a bit askew compared to what is accepted today, he set forth the idea that matter must be conserved. He also invented coordinate geometry, it was his idea to measure something by its relation to two fixed lines.  The Cartesian coordinate system gets its name from Descartes.   He also started describing shapes as equations and was instrumental in laying the foundations for algebra, earning his title of the father of analytical geometry.

However great these achievements, enlightenment in philosophy was arguably his most passionate endeavor.  He spent nearly 20 years asking what he could know and what he was.  These questions motivated his quest for mathematical and scientific knowledge.

They also shed light onto his outlook on life, which despite being focused on doubting everything, became relevant lately in Tali Sharot’s history of optimism in her book, The Optimism Bias. Sharot says, “Descartes  was one of the first philosophers to express optimistic idealization, in his trust that humans could master their own universe and thereby enjoy the fruits of the earth and the maintenance of good health.”