March 31, 1596: René Descartes is born
René Descartes (1596-1650)
Scientific field: Mathematics
Known for: Cartesian coordinate system
René Descartes was a French mathematician, scientist, and philosopher, one of the first to abandon scholastic Aristotelianism. Because he formulated the first modern version of mind-body dualism, from which stems the mind-body problem, and because he promoted the development of a new science grounded in observation and experiment, he has been called the father of modern philosophy.
Applying an original system of methodical doubt, he dismissed apparent knowledge derived from authority, the senses, and reason and erected new epistemic foundations on the basis of the intuition that, when he is thinking, he exists; this he expressed in the dictum “I think, therefore I am” (best known in its Latin formulation, “Cogito, ergo sum”, though originally written in French, “Je pense, donc je suis”). He developed a metaphysical dualism that distinguishes radically between mind, the essence of which is thinking, and matter, the essence of which is extension in three dimensions. Descartes’s metaphysics is rationalist, based on the postulation of innate ideas of mind, matter, and God, but his physics and physiology, based on sensory experience, are mechanistic and empiricist.(1)
Descartes’s philosophy, sometimes called Cartesianism, carried him into elaborate and erroneous explanations of a number of physical phenomena. These explanations, however, had value, because he substituted a system of mechanical interpretations of physical phenomena for the vague spiritual concepts of most earlier writers. Although Descartes had at first been inclined to accept the Copernican theory of the universe with its concept of a system of spinning planets revolving around the sun, he abandoned this theory when it was pronounced heretical by the Roman Catholic Church. In its place he devised a theory of vortices in which space was entirely filled with matter, in various states, whirling about the sun.
Descartes’s study of optics led him to the independent discovery of the fundamental law of reflection: that the angle of incidence is equal to the angle of reflection. His essay on optics was the first published statement of this law. Descartes’s treatment of light as a type of pressure in a solid medium paved the way for the undulatory theory of light.
The most notable contribution that Descartes made to mathematics was the systematization of analytic geometry. He was the first mathematician to attempt to classify curves according to the types of equations that produce them. He also made contributions to the theory of equations. Descartes was the first to use the last letters of the alphabet to designate unknown quantities and the first letters to designate known ones. He also invented the method of indices (as in x2) to express the powers of numbers. In addition, he formulated the rule, which is known as Descartes’s rule of signs, for finding the number of positive and negative roots for any algebraic equation.(2)
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