In 1633, the year that Italian scientist Galileo was forced to recant by the Inquisition, René Descartes was just finishing his first major scientific treatise, Le Monde (The World, 1998). In the work, Descartes had used the Copernican theory for which, in part, Galileo had been condemned, so prudence dictated that the work be withheld from publication. However, a strong sense of the importance of his discoveries caused him to issue three token essays and to compose a kind of prospectus of his work to date for publication under the same cover. The latter is the Discourse on Method. Besides explaining the author’s method and reviewing his labors, it summarizes his metaphysical reasoning and sketches the plan of the larger, unpublished volume. Strangely, perhaps, for one whose declared intention was to set all human knowledge on impersonal foundations, the Discourse on Method is a highly personal communication. It begins with a biographical reminiscence.

The Young Descartes

Familiar with books from childhood, the young Descartes entered the new Jesuit Collège de La Flèche with high expectation, but he early fell victim to the skepticism that attended the passing of the Renaissance. The study of ancient tongues, classic treatises on morals and philosophy, and jurisprudence and medicine were excellent for ornamenting the person and preparing one for a life of riches and honor, but Descartes decided that they yielded nothing that could be called knowledge. The only good to come from the revival of learning, so far as truth is concerned, was the rediscovery of mathematics, which, however, he was inclined to take without the Pythagorean mystifications that so delighted German astronomer Johannes Kepler. The thing that pleased Descartes in mathematics was the certitude and evidence that accompanied its demonstrations, and he was surprised to find that no higher science had been erected on such solid foundations. By contrast, philosophy, on which so much had been based, could exhibit no single claim that was not in dispute.

The young graduate had no further incentive toward books or toward the past. On the hunch that practical people might be wiser than scholars, in that they cannot entertain follies with impunity, Descartes resolved to see the world and talk with people of every rank and occupation. He soon found, however, that practical people disagree as much as do philosophers, and as for the experience of traveling in foreign lands, nothing so quickly undermines one’s confidence in the judgment of one’s fellow humans.

A Turning Point

Then came the turning point in Descartes’s life. While he was still in his early twenties, he made the discovery—for which he is celebrated in the history of mathematics—that it is possible to bring geometry and algebra together into a single science by plotting equations along rectangular axes. This startling discovery encouraged him to look into his own mind for still more fundamental truths:I resolved at length to make myself an object of study, and to employ all the powers of my mind in choosing the paths I ought to follow.

It was the winter of 1619-1620, and Descartes was in Germany, serving in the army, twenty-three years old. For another nine years, he was content to travel, assuming the role of spectator rather than actor in the affairs of the world. However, he was not wasting his time. Part of his program consisted in systematic doubt; by painstaking reflection upon every matter that could be a source of error, he deliberately attempted to destroy beliefs that were not certainly true.

At the end of this period, he moved to Holland, ready to undertake the recovery of truth. His first step was to replace the old metaphysics with one founded on his newly formed principles, which he did in Meditationes de prima philosophia (1641; Meditations on First Philosophy, written in 1628-1629 although not published for more than ten years). This accomplished, he was free to set about his main enterprise, which was to lay bare the secret laws that govern the world of matter. In the next eight years, his progress was astonishing. However, the innumerable experiments that kept suggesting themselves required many hands. His motive in presenting the summary of his ideas in the Discourse on Method was to recruit workers.

Out of Skepticism

There is evidence independent of the Discourse on Method that the first powerful conviction that lifted Descartes out of skepticism was the discovery of certain rules for the direction of the mind. In the Discourse on Method, he associates this phase of his development with the winter in Germany when he was twenty-three. It antedates his enterprise of systematic doubt and, indeed, is presupposed by it, the doubt being but the first step toward carrying through the rules.

The brilliant young mathematician was led to conclude that just as the most difficult demonstrations in geometry can be arrived at easily by a long chain of simple steps, soall things, to the knowledge of which man is competent, are mutually connected in the same way, and . . . there is nothing so far removed from us as to be beyond our reach, or so hidden that we cannot discover it, provided only we abstain from accepting the false for the true, and always preserve in our thoughts the order necessary for the deduction of one truth from another.

What Descartes had discovered, he believed, was a key that would open for humankind all the doors to knowledge. No new power of insight or of reasoning was needed—every person, essentially, has as much insight and reason as any other. The failure of previous inquirers stemmed from no natural deficiency but from clumsiness and inexperience. Chiefly, people had been seduced by the powerful claims of their senses and imagination so that the sober witness of reason had been obscured. What people needed was a set of rules that would help them to keep faithfully to truths that, once the debris had been removed, would shine upon the mind with a natural light.

The Method

Descartes was, therefore, a bold exponent of what is known as the deductive or a priori method. Still, his approach must not be confused with the Scholasticism that, in philosopher Francis Bacon’s words, “flies from the senses and particulars to the most general axioms, and from these principles, the truth of which it takes for settled and immoveable, proceeds to judgment and to the discovery of middle axioms.” The fault of the Aristotelian syllogism, Descartes said, was that, although it helps people reason persuasively about things they already think they know, it is of no help in investigating the unknown. Thus, Descartes’s method was more radically a priori than Aristotle’s, which drew its premises from induction.

Turning his back on traditional logic and taking his cue from geometry, Descartes envisaged a chain of linear inferences that would progress from an initial truth so simple and obvious as to be self-evident to a second that would be seen at once to be included in the first, and thence to a third, and so forth. In practice, the problem would always be to find the simple truth to which the chain could be anchored; afterward, all that would be necessary would be to preserve the true order. Each particular truth along the way would be entirely obvious to anyone who understood what was being affirmed—just as in arithmetic, a child who understands a sum fathoms everything that is within reach of the greatest genius who contemplates the same set of figures.

For convenience, Descartes summed up his principles in four rules:1. Never accept any idea as true that is not so clearly and distinctly true as to be beyond all possibility of being doubted. 2. Divide each complex question into simple ones. 3. Order thoughts from the simplest to the most complex. 4. Review the series of inferences to make sure there are no breaks or false links in the chain.

If these rules were rigorously followed, an obscure matter, such as the function of the lungs in the body, would be rendered perfectly intelligible. Such, at least, was the promise that inspired the youthful Descartes and launched him on his great career.

The Metaphysical

The biographical narrative and the exposition of method make up the first half of the Discourse on Method. Part 4 is an abridged version of the Meditations on First Philosophy. Descartes’s preeminently scientific interests seem somewhat incompatible with his foray into the metaphysical. However, as he explained, to have ventured at once into the difficulties of the sciences would have been contrary to right order because he regarded all such particular truths as dependent on principles borrowed from philosophy.

The investigation of the principles set forth in part 4 was “so metaphysical and uncommon” that Descartes questioned whether his readers would find it acceptable. It is, in fact, the only part of the Discourse on Method that makes serious demands upon the intelligence. Yet, because the Meditations on First Philosophy had not been published in 1637, he felt obliged to include a précis of that work. This review of the work places it in its proper perspective—as the first serious attempt to make use of the method of doubt and as the foundation for physics and physiology rather than an end in itself. Lacking this perspective, one might suppose that Descartes’s preoccupation with God and the soul stemmed from a religious interest. His Scholastic-styled proofs suggest to the modern reader that he is laboring to shore up traditional beliefs. However, when Descartes speaks of soul, he means “thinking” (and ideally “reasoning,” for all the rest of the conscious life is illusion), and when he speaks of God, he means the “ordered necessity” against which all apparent “contingency” is rendered intelligible. Therefore, far from seeking to preserve the Christian view of the world, he is substituting for it an uncompromising formulation of the presuppositions of seventeenth and eighteenth century science. Just how far his philosophical work strengthened the cause of science and speeded its development is impossible to say, but it seems likely that his metaphysics was more useful than his method.

Thought and the Existence of God

The method required that Descartes discover a truth so simple and self-evident that it could not be further reduced and yet would verify itself. Yet every belief he considered seemed to him to be a possible error. He supposed that even his strongest convictions might have been planted in him by a malevolent and deceiving god. However, finally it struck him that even though his beliefs were mistaken and he could not go beyond the activity of doubting, the doubting itself existed; thinking existed; and if thinking, then he, as thinking substance, also existed. He expressed his conclusion in the triumphant words Cogito, ergo sum, or “I think, therefore I am.”

When he sought to discover the ground of his...

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Human Physiology

The greater part of the summary is given to human physiology. Continuing his hypothetical mode of argument, Descartes asks one to think of God as forming the body of a person exactly like one’s own but without a rational soul. This being granted, Descartes undertook to show how, according to the same laws as obtain everywhere else in nature, all the internal and external motions of the body must take place exactly as they are observed to take place, with the exception of intelligent speech and certain inventive actions. The circulation of the blood is taken as an example. Its motion through the body, as Descartes explains it, is the result of the presence in the heart of one of those fires-without-light (the kind present in...

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Additional Reading

Beck, L. J. The Method of Descartes. New York: Garland, 1987. Provides a clear exposition of the Discourse on Method which, though scholarly, is easily understandable.

Chappell, Vere, ed. Descartes’s Meditations: Critical Essays. Lanham, Md.: Rowman and Littlefield, 1997. A significant collection of essays by scholars who carefully assess the perspectives and problems in one of Western philosophy’s most important texts.

Copleston, Frederick. A History of Philosophy: Modern Philosophy. Garden City, N.Y.: Doubleday, 1964. Copleston situates René...

(The entire section is 539 words.)