Discourse on Method

Descartes tells the story of his schooling and his travels, explains why he decided to doubt everything he had been taught, and sets out four simple rules for thinking clearly. From that doubt he reaches the famous conclusion "I think, therefore I am", and builds outward to God, the body and the natural world. He wrote it in French rather than Latin, so that any reader with good sense could follow him. This is John Veitch's clear translation of 1850. It can be read in an evening.

Original work: Written in French, published 1637