René Descartes

Born in La Haye, France, René Descartes (1596–1650) worked for several years as a military engineer before writing revolutionary works in philosophy, mathematics, and science. His philosophy is known today as Cartesianism or Cartesian philosophy.

Descartes’ philosophical project was to replace the Aristotelian system of science that was then the basis of university education in France and throughout Europe. His most important work arguably was his Meditations on First Philosophy (1641). The book recounted his thoughts over six days spent in a small room during his travels. Descartes attempted to question all of his beliefs and retain only those whose truth he could not doubt. It was during this effort that Descartes made his famous observation that because he could not doubt he thinks, he could not doubt he exists—“I think, therefore I am,” or, in the original Latin, “Cogito, ergo sum.”

While Descartes concluded his fundamental existence was not in doubt, he believed he could doubt the nature of his body. Because his ability to think was irrefutable but the existence of his physical body was not, Descartes argued that mind and body are distinct. Descartes believed bodies were described by physics. They are geometrical things in motion with size, shape, and velocity. Minds, on the other hand, are immaterial thinking things. Hence, for Descartes, animals were mere machines. Because they do not think (he assumed), they do not have minds, and they must simply be complex arrangements of moving parts.


  1. Descartes called bodies res extensa—extended things—and minds res intelligens—thinking things.
  2. Descartes invented analytic geometry also called coordinate geometry

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