Descartes wrote his most famous line in French, not Latin, in 1637
"I think, therefore I am" first appeared in a short French treatise that was meant as a mere preface. René Descartes published it in Leiden in 1637 to introduce three scientific essays, one of which planted the seed of Cartesian coordinates. The preface outlived its companions and reshaped modern philosophy.
The full title promises a method for conducting reason well and seeking truth in the sciences. Descartes blended autobiography with argument, telling how he arrived at his rules rather than simply laying them down. It appeared in the Netherlands, and a Latin version followed in Amsterdam in 1656, widening its reach among scholars across Europe.
Its original job was introductory. Three works came bundled with it: La Dioptrique on optics, Les Météores on weather, and La Géométrie. That last essay contained the early ideas that grew into the Cartesian coordinate system, so a single volume carried both a new approach to doubt and a tool that algebra and geometry students still use.
Descartes split the text into six parts. They move from general reflections on learning, through the core rules of his method and a provisional moral code, to arguments for God and the soul, then to physics, the motion of the heart and the gap he saw between humans and animals, and finally to what future research would need. The central problem was skepticism: earlier thinkers had shown how little could be known for sure, and Descartes adjusted their approach until he reached one truth he considered impossible to doubt, his own thinking existence.
The opening shows a dry sense of humour. Good sense, he jokes, must be the most evenly shared thing on earth, since nobody ever wishes for more of it. Hobbes and Montaigne made similar remarks, which suggests the quip was a commonplace of the age. His serious point follows at once: a strong mind matters less than using it correctly, and a slow walker on the right road outpaces a runner who strays. Alongside the Meditations and the Principles of Philosophy, the book forms the foundation of Cartesianism.
Source: Discourse on the Method
