“Cogito, ergo sum.” (“I think, therefore I am.”)
– René Descartes, in his works “Discourse on the Method” (1637) and “Principles of Philosophy” (1644) – both works give the Latin version, although the earlier work also gave a French version (“Je pense, donc je suis”) that is actually the original
People know René Descartes more for his mathematics than for his philosophy. If you’ve ever taken algebra, you’ve probably seen two-dimensional equations graphed on what is still called a “Cartesian” coordinate plane. It is named after him for good reason, for he pioneered this “merging together” of algebra and geometry. But Descartes was also a very influential philosopher, who took part in the age-old debates over what is the most reliable basis of human knowledge. He answered that it was “reason,” and many in the Western world have since followed his lead in this regard.