- René Descartes (plato.standford.edu)
René Descartes (1596–1650) was a creative mathematician of the first order, an important scientific thinker, and an original metaphysician. During the course of his life, he was a mathematician first, a natural scientist or “natural philosopher” second, and a metaphysician third. In mathematics, he developed the techniques that made possible algebraic (or “analytic”) geometry. In natural philosophy, he can be credited with several achievements: the first to publish the sine law of refraction; developer of an important empirical account of the rainbow; and proposer of a naturalistic account of the formation of the earth and planets (a precursor to the nebular hypothesis, that the planets formed from loose matter orbiting the sun). More importantly, he offered a new vision of the natural world, which shaped modern physics: a world of matter possessing a few fundamental properties and interacting according to a few universal laws. This natural world included an immaterial mind that, in human beings, was directly related to the brain, a position that led to the modern mind–body problem. In metaphysics (the search for the basic principles of everything there is), Descartes provided arguments for the existence of God and to show that the essence of matter is to be spatially extended, and that the essence of mind is thought (where “thought” includes sensory images as well as rational discourse). Descartes claimed early on to possess a special method, which was variously exhibited in mathematics, natural philosophy, and metaphysics, and which came to include, or to be supplemented by, a method of doubt.
- Cogito, ergo sum (Wikipedia)
The Latin cogito, ergo sum, usually translated into English as “I think, therefore I am”, is the “first principle” of René Descartes’s philosophy. He originally published it in French as je pense, donc je suis in his 1637 Discourse on the Method, so as to reach a wider audience than Latin would have allowed. It later appeared in Latin in his Principles of Philosophy, and a similar phrase also featured prominently in his Meditations on First Philosophy. The dictum is also sometimes referred to as the cogito. As Descartes explained in a margin note, “we cannot doubt of our existence while we doubt.” In the posthumously published The Search for Truth by Natural Light, he expressed this insight as dubito, ergo sum, vel, quod idem est, cogito, ergo sum (“I doubt, therefore I am — or what is the same — I think, therefore I am”). Antoine Léonard Thomas, in a 1765 essay in honor of Descartes presented it as dubito, ergo cogito, ergo sum (“I doubt, therefore I think, therefore I am”).