René (1596–1650), French philosopher and mathematician, a founder of the ‘modern age’ and perhaps the most important figure in the intellectual revolution of the seventeenth century in which the traditional systems of understanding based on Aristotle were challenged and, ultimately, overthrown. His conception of philosophy was all-embracing: it encompassed mathematics and the physical sciences as well as psychology and ethics, and it was based on what he claimed to be absolutely firm and reliable metaphysical foundations. His approach to the problems of knowledge, certainty, and the nature of the human mind played a major part in shaping the subsequent development of philosophy. Life and works. Descartes was born in a small town near Tours that now bears his name. He was brought up by his maternal grandmother (his mother having died soon after his birth), and at the age of ten he was sent to the recently founded Jesuit college of La Flèche in Anjou, where he remained as a boarding pupil for nine years. At La Flèche he studied classical literature and traditional classics-based subjects such as history and rhetoric as well as natural philosophy (based on the Aristotelian system) and theology. He later wrote of La Flèche that he considered it ‘one of the best schools in Europe,’ but that, as regards the philosophy he had learned there, he saw that ‘despite being cultivated for many centuries by the best minds, it contained no point which was not disputed and hence doubtful.’ At age twenty-two (having taken a law degree at Poitiers), Descartes set out on a series of travels in Europe, ‘resolving,’ as he later put it, ‘to seek no knowledge other than that which could be found either in myself or the great book of the world.’ The most important influence of this early period was Descartes’s friendship with the Dutchman Isaac Beeckman, who awakened his lifelong interest in mathematics – a science in which he discerned precision and certainty of the kind that truly merited the title of scientia (Descartes’s term for genuine systematic knowledge based on reliable principles). A considerable portion of Descartes’s energies as a young man was devoted to pure mathematics: his essay on Geometry (published in 1637) incorporated results discovered during the 1620s. But he also saw mathematics as the key to making progress in the applied sciences; his earliest work, the Compendium Musicae, written in 1618 and dedicated to Beeckman, applied quantitative principles to the study of musical harmony and dissonance. More generally, Descartes saw mathematics as a kind of paradigm for all human understanding: ‘those long chains composed of very simple and easy reasonings, which geometers customarily use to arrive at their most difficult demonstrations, gave me occasion to suppose that all the things which fall within the scope of human knowledge are interconnected in the same way’ (Discourse on the Method, Part II).
In the course of his travels, Descartes found himself closeted, on November 10, 1619, in a ‘stove-heated room’ in a town in southern Germany, where after a day of intense meditation, he had a series of vivid dreams that convinced him of his mission to found a new scientific and philosophical system. After returning to Paris for a time, he emigrated to Holland in 1628, where he was to live (though with frequent changes of address) for most of the rest of his life. By 1633 he had ready a treatise on cosmology and physics, Le Monde; but he cautiously withdrew the work from publication when he heard of the condemnation of Galileo by the Inquisition for rejecting (as Descartes himself did) the traditional geocentric theory of the universe. But in 1637 Descartes released for publication, in French, a sample of his scientific work: three essays entitled the Optics, Meteorology, and Geometry. Prefaced to that selection was an autobiographical introduction entitled Discourse on the Method of rightly conducting one’s reason and reaching the truth in the sciences. This work, which includes discussion of a number of scientific issues such as the circulation of the blood, contains (in Part IV) a summary of Descartes’s views on knowledge, certainty, and the metaphysical foundations of science. Criticisms of his arguments here led Descartes to compose his philosophical masterpiece, the Meditations on First Philosophy, published in Latin in 1641 – a dramatic account of the voyage of discovery from universal doubt to certainty of one’s own existence, and the subsequent struggle to establish the existence of God, the nature and existence of the external world, and the relation between mind and body. The Meditations aroused enormous interest among Descartes’s contemporaries, and six sets of objections by celebrated philosophers and theologians (including Mersenne, Hobbes, Arnauld, and Gassendi) were published in the same volume as the first edition (a seventh set, by the Jesuit Pierre Bourdin, was included in the second edition of 1642). A few years later, Descartes published, in Latin, a mammoth compendium of his metaphysical and scientific views, the Principles of Philosophy, which he hoped would become a university textbook to rival the standard texts based on Aristotle. In the later 1640s, Descartes became interested in questions of ethics and psychology, partly as a result of acute questions about the implications of his system raised by Princess Elizabeth of Bohemia in a long and fruitful correspondence. The fruits of this interest were published in 1649 in a lengthy French treatise entitled The Passions of the Soul. The same year, Descartes accepted (after much hesitation) an invitation to go to Stockholm to give philosophical instruction to Queen Christina of Sweden. He was required to provide tutorials at the royal palace at five o’clock in the morning, and the strain of this break in his habits (he had maintained the lifelong custom of lying in bed late into the morning) led to his catching pneumonia. He died just short of his fifty-fourth birthday. The Cartesian system. In a celebrated simile, Descartes described the whole of philosophy as like a tree: the roots are metaphysics, the trunk physics, and the branches are the various particular sciences, including mechanics, medicine, and morals. The analogy captures at least three important features of the Cartesian system. The first is its insistence on the essential unity of knowledge, which contrasts strongly with the Aristotelian conception of the sciences as a series of separate disciplines, each with its own methods and standards of precision. The sciences, as Descartes put it in an early notebook, are all ‘linked together’ in a sequence that is in principle as simple and straightforward as the series of numbers. The second point conveyed by the tree simile is the utility of philosophy for ordinary living: the tree is valued for its fruits, and these are gathered, Descartes points out, ‘not from the roots or the trunk but from the ends of the branches’ – the practical sciences. Descartes frequently stresses that his principal motivation is not abstract theorizing for its own sake: in place of the ‘speculative philosophy taught in the Schools,’ we can and should achieve knowledge that is ‘useful in life’ and that will one day make us ‘masters and possessors of nature.’ Third, the likening of metaphysics or ‘first philosophy’ to the roots of the tree nicely captures the Cartesian belief in what has come to be known as foundationalism – the view that knowledge must be constructed from the bottom up, and that nothing can be taken as established until we have gone back to first principles.
Doubt and the foundations of belief. In Descartes’s central work of metaphysics, the Meditations, he begins his construction project by observing that many of the preconceived opinions he has accepted since childhood have turned out to be unreliable; so it is necessary, ‘once in a lifetime’ to ‘demolish everything and start again, right from the foundations.’ Descartes proceeds, in other words, by applying what is sometimes called his method of doubt, which is explained in the earlier Discourse on the Method: ‘Since I now wished to devote myself solely to the search for truth, I thought it necessary t. . . reject as if absolutely false everything in which one could imagine the least doubt, in order to see if I was left believing anything that was entirely indubitable.’ In the Meditations we find this method applied to produce a systematic critique of previous beliefs, as follows. Anything based on the senses is potentially suspect, since ‘I have found by experience that the senses sometimes deceive, and it is prudent never to trust completely those who have deceived us even once.’ Even such seemingly straightforward judgments as ‘I am sitting here by the fire’ may be false, since there is no guarantee that my present experience is not a dream. The dream argument (as it has come to be called) leaves intact the truths of mathematics, since ‘whether I am awake or asleep two and three make five’; but Descartes now proceeds to introduce an even more radical argument for doubt based on the following dilemma. If there is an omnipotent God, he could presumably cause me to go wrong every time I count two and three; if, on the other hand, there is no God, then I owe my origins not to a powerful and intelligent creator, but to some random series of imperfect causes, and in this case there is even less reason to suppose that my basic intuitions about mathematics are reliable. By the end of the First Meditation, Descartes finds himself in a morass of wholesale doubt, which he dramatizes by introducing an imaginary demon ‘of the utmost power and cunning’ who is systematically deceiving him