DESCARTES, RENÉ DU PERRON (b. La Haye, Touraine, France, 31 March 1596; d. Stockholm, Sweden, 11 February 1650), natural philosophy, scientific method, mathematics, optics, mechanics, physiology.

Fontenelle, in the eloquent contrast made in his Éloge de Newton, described Descartes as the man who “tried in one bold leap to put himself at the source of everything, to make himself master of the first principles by means of certain clear and fundamental ideas, so that he could then simply descend to the phenomena of nature as to necessary consequences of these principles.” This famous characterization of Descartes as the theoretician who “set out from what he knew clearly, in order to find the cause of what he saw,” as against Newton the experimenter, who “set out from what he saw, in order to find the cause,” has tended to dominate interpretations of both these men who “saw the need to carry geometry into physics.”1

Descartes was born into the noblesse de robe, whose members contributed notably to intellectual life in seventeenth-century France. His father was conseiller to the Parlement of Brittany; from his mother he received the name du Perron and financial independence from property in Poitou. From the Jesuits of La Flèche he received a modern education in mathematics and physics—including Galileo's telescopic discoveries—as well as in philosophy and the classics, and there began the twin domination of imagination and geometry over his precocious mind. He described in an early work, the Olympica, how he found “in the writings of the poets weightier thoughts than in those of the philosophers. The reason is that the poets wrote through enthusiasm and the power of imagination.” The seeds of knowledge in us, “as in a flint,” were brought to light by philosophers “through reason; struck out through imagination by poets they shine forth more brightly.”2 Then, after graduating in law from the University of Poitiers, as a gentleman volunteer in the army of Prince Maurice of Nassau in 1618 he met Isaac Beeckman at Breda. Beeckman aroused him to self-discovery as a scientific thinker and mathematician and introduced him to a range of problems, especially in mechanics and acoustics, the subject of his first work, the Compendium musicae of 1618; published posthumously in 1650. On 26 March 1619 he reported to Beeckman his first glimpse of “an entirely new science,”3 which was to become his analytical geometry.

Later in the year, on 10 November, then in the duke of Bavaria's army on the Danube, he had the experience in the famous poêle (lit. “stove,” “well-heated room”), claimed to have given direction to the rest of his life. He described in the Discours de la méthode how, in a day of solitary thought, he reached two radical conclusions: first, that if he were to discover true knowledge he must carry out the whole program himself, just as a perfect work of art or architecture was always the work of one master hand; second, that he must begin by methodically doubting everything taught in current philosophy and look for self-evident, certain principles from which to reconstruct all the sciences. That night, according to his seventeenth-century biographer Adrien Baillet, these resolutions were reinforced by three consecutive dreams. He found himself, first, in a street swept by a fierce wind, unable to stand, as his companions were doing, because of a weakness in his right leg; second, awakened by a clap of thunder in a room full of sparks; and third, with a dictionary, then a book in which he read Quid vitae sectabor iter? (“What way of life shall I follow?”), then verses presented by an unknown man beginning Est et non; he recognized the Latin as the opening lines of two poems by Ausonius. Before he finally awoke he had interpreted the first dream as a warning against past errors, the second as the descent of the spirit of truth, and the third as the opening to him of the path to true knowledge. However this incident may have been elaborated in the telling, it symbolizes both the strength and the hazards of Descartes's unshakable confidence and resolve to work alone. But he did not make his vision his life's mission for another nine years, during which (either before or after his tour of Italy from 1623 to 1625) he met Mersenne, who was to become his lifelong correspondent, and took part in scientific meetings in Paris. The next decisive incident, according to Baillet, was a public encounter in 1628 in which he demolished the unfortunate Chandoux by using his method to distinguish sharply between true scientific knowledge and mere probability. Among those present was