30 Philosophers, Chapter 22: Descartes and Cartesian Dualism.

René Descartes was born into minor nobility in 1596, and lived during the Scientific Revolution. He is important because he became dissatisfied with inherited teachings and searched for a more dependable foundation for knowledge. In 1637, he published Discourse on the Method. In this book, he introduced his disciplined process of questioning beliefs, an early treasure of a work for a great mind. Essentially it boiled down to this: rather than accepting knowledge merely because they were traditional, authoritative, or familiar, you discover why.

This process became known as Cartesian Skepticism, or methodic doubt. Descartes temporarily suspended any belief that could be doubted, including the evidence of his senses. He even imagined that an evil demon might be manipulating his thoughts. Yet the act of doubting revealed one certainty: something must exist to do the doubting. He captured this in his famous statement, *Cogito, ergo sum*—“I think, therefore I am.” It was a brilliant thought experiment, but a strange one too. Descartes used an irrational possibility to tear knowledge down, then tried to rebuild it from the thinking mind.

Descartes also argued that the mind and body were fundamentally different substances, a position now called Cartesian Dualism. The body occupied physical space, while the mind thought and experienced. But to rebuild knowledge, he soon relied on another supernatural step: a perfect God who would not deceive us. In that sense, Descartes tore knowledge down and rebuilt it using irrational tools. His journey into doubt was groundbreaking and remains useful, but his doubt deserves some doubt of its own.