Discourse on the Method by René Descartes is about how he developed his philosophy and approach to thinking. Descartes starts by questioning everything he had been taught and anything that could be doubted, ultimately concluding that the only thing he could be certain of was his own existence — famously stating "I think, therefore I am." He argues that knowledge should be built on clear, logical reasoning and that science and philosophy should be grounded in doubt and skepticism until something is proven to be true. Descartes’ work laid the foundation for modern philosophy and the scientific method, emphasizing the importance of doubt and careful thinking in the pursuit of truth.