"If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things."
There is a story about René Descartes (1596 – 1650), that he once attended a lecture held by a chemist named Chandoux. Chandoux criticized Aristotle, who had been *the* philosopher of Europe for over a thousand years. Everyone in the audience was greatly impressed, except for Descartes. A Cardinal named Bérulle, who happened to be in the audience, noticed this, and asked Descartes for the reason. After polite attempts at evasion proved futile, Descartes eventually explained that, although Chandoux was quite right in criticizing Aristotle, he had not shown how his ideas could be replaced. To illustrate his point, he asked the audience to name a self-evident truth. When they did, he produced twelve plausible reasons why it could not be true. Then he asked them to name a self-evident falsehood, and similarly produced arguments for its truth. The most important questions in philosophy, he concluded, could not be proven or disproved definitively, unless questions of methodology were first resolved. Afterwards, the Cardinal invited Descartes to his home, and told him that, since God had given him such amazing fits, it was his duty to develop his talents and put them in the service of mankind. Descartes resolved to do just that.
His major works were his Discourse on Method (1637) and his Meditation on First Principles (1641), in which he proposed to answer the doubts he raised with Chandoux.
According to Descartes, truth can be known in two ways: through the clarity and vividness of our ideas, and through logical deduction from the same. Just as in geometry everything follows from a handful of starting principles, and everything that does follow is as certain as these principles, in philosophy all reasoning should proceed by deduction from clear and vivid ideas. Observation could not (as Bacon had argued), form a methodologically sound basis for philosophy, because the senses are not themselves reliable. One person has better sight than another, and a third has no sight at all. The things we see in dreams seem as real to us as those we see when we wake, and when we do wake we have no way to know whether or not we are, after all, still dreaming. Observation is important in science (clearly), but we need to reason methodically about our observations, and when they conflict with reason, we should privilege the latter over the former.
On this basis Descartes proved the existence of the self, of God, of free will, the soul, space, time, motion, and many other things. It is not the content of his philosophy on which his fame rests, however, but his method. European intellectuals had been dissatisfied with tradition in one way or another for generations before him, but they had resolved these difficulties by privileging one part of tradition over another. Martin Luther and John Calvin had rejected Aristotle and the theologians, but strengthened the authoritative status of the Bible. Their Catholic opponents had responded by aggressively reasserting the authority of both Aristotle and the Theologians. Bacon had proposed a new method for natural philosophy, but he had not rejected the authority of tradition in ethics, politics, aesthetics, or other areas outside of natural philosophy. The uniqueness of Descartes’ position lay in his rejection of everything that could not be demonstrated through reason – even belief in God had to stand or fall on reason alone (though, as we have seen, he thought it did pass this test.) This characteristically modern attitude has proven endlessly subversive and revolutionary in subsequent intellectual history, and has become so established that it seems the plainest common sense today. It was, nevertheless, an important advance for science.
Descartes also made an important contribution to mathematics when he invented the coordinate plane. Because any algebraic equation can be graphed, and any graph expressed as an algebraic equation, it effectively bridged the gap between algebra and geometry, and made possible new methods in calculus, navigation, and engineering. His theory of vortices is also one of the great “also rans” of physics. Aside from these contributions, Descartes is also important for giving primacy to reason over observation, which has remained the dominant trend in European intellectual life up to the present (the Anglophone tradition, by contrast, follows Bacon and gives priority to observation.)
Descarte's preoccupation with defeating skepticism and establishing knowledge on a certain basis reflects the uncertainty of the Early Modern period. The intellectual world of the ancients was based on trust - the old ways, the old books, and the old thoughts were best. Everything worth knowing, it seemed, had been known and said of old, and it was therefor the business of people in the present not to make new discoveries, but to retain and apply what had already been discovered. This belief was profoundly shaken by the discovery of the New World, that the world was not at the center of the cosmos, and that, in general, there were all sorts of discoveries waiting to be made, about which the ancient masters had known nothing. If even they could be doubted, what could not? This situation seemed to Descartes, and to many of his contemporaries, intolerable - hence his lifelong preoccupation with establishing a method by which truth could be known with certainty.
Never in good health, he died of pneumonia in 1650, after a year teaching philosophy in Sweden.
SEP: http://plato.stanford.edu/entries/descartes/
Part of a series on the Enlightenment
Part of a series on Science, Technology, and Society (III of XX)
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