Discourse on the Method is Descartes’ attempt to explain his method of reasoning through even the most difficult of problems. He illustrates the development of this method through brief autobiographical sketches interspersed with philosophical arguments.
Part 1 contains “various considerations concerning the sciences.” First, all people possess “good sense,” the ability to distinguish truth from fiction. Therefore, it is not a lack of ability that obstructs people but their failure to follow the correct path of thought. The use of a method can elevate an average mind above the rest, and Descartes considered himself a typical thinker improved by the use of his method. Descartes benefited from a superior education, but he believed that book learning also clouded his mind. After leaving school, he set off traveling to learn from “the great book of the world” with an unclouded mind. He comes to the conclusion that all people have a “natural light” that can be obscured by education and that it is as important to study oneself as it is to study the world.
In part 2, Descartes describes his revelation in the “stove-heated room.” Contemplating various subjects, he hits on the idea that the works of individuals are superior to those conceived by committee because an individual’s work follows one plan, with all elements working toward the same end. He considers that the science he learned as a boy is likely flawed because it consists of the ideas of many different men from various eras. Keeping in mind what he has learned of logic, geometry, and algebra, he sets down the following rules: (1) to never believe anything unless he can prove it himself; (2) to reduce every problem to its simplest parts; (3) to always be orderly in his thoughts and proceed from the simplest part to the most difficult; and (4) to always, when solving a problem, create a long chain of reasoning and leave nothing out. He immediately finds this method effective in solving problems that he had found too difficult before. Still fearing that his own misconceptions might be getting in the way of pure reason, he decides to systematically eliminate all his wrong opinions and use his new method exclusively.
In part 3, Descartes puts forth a provisional moral code to live by while rethinking his views: (1) to obey the rules and customs of his country and his religion and never take an extreme opinion; (2) to be decisive and stick with his decisions, even if some doubts linger; (3) to try to change himself, not the world; and (4) to examine all the professions in the world and try to figure out what the best one is. Not surprising, Descartes determines that reasoning and searching for the truth is, if not the highest calling, at least extremely useful. For many years after his revelation, Descartes traveled widely and gained a reputation for wisdom, then retired to examine his thoughts in solitude.
In part 4, Descartes offers proofs of the existence of the soul and of God. Contemplating the nature of dreams and the unreliability of the senses, he becomes aware of his own process of thinking and realizes it is proof of his existence: I think, therefore I exist (Cogito ergo sum). He also concludes that the soul is separate from the body based on the unreliability of the senses as compared with pure reason. His own doubts lead him to believe that he is imperfect, yet his ability to conceive of perfection indicates that something perfect must exist outside of him—namely, God. He reasons that all good things in the world must stem from God, as must all clear and distinct thoughts.
Part 5 moves from discussion of a theory of light to theories about human anatomy. Descartes considers the fact that animals have many of the same organs as humans yet lack powers of speech or reason. He takes this difference to be evidence of humankind’s “rational soul.” He considers the mysterious connection of the soul to the body and concludes that the soul must have a life outside the body. Therefore it must not die when the body dies. Because he cannot conceive of a way that the soul could perish or be killed, he is forced to conclude that the soul is immortal.
In part 6, Descartes cautiously touches on possible conflicts with the church over his ideas about physical science. Finally, he implores his readers to read carefully, apologizes for writing in French rather than Latin, and vows to shun fame and fortune in the name of pursuing truth and knowledge.
Discourse on the Method (1637) was Descartes’ first published work. He wrote the book in French rather than Latin, the accepted language of scholarship at the time, because he intended to explain complex scientific matters to people who had never studied them before.
Descartes’ education was based on the Aristotelian model of reasoning, which held that scientific knowledge is deduced from fixed premises. This model is based on the syllogism, in which one starts with a major premise (“Virtues are good”) and a minor premise (“kindness is a virtue”), then draws a conclusion from the two (“therefore, kindness must be good”). Descartes wondered whether he could be certain of the premises he had been taught. He was reasonably convinced of the certainty of mathematics (at which he excelled), but the other sciences seemed shaky to him because they were based on philosophical models rather than rational tests, which seemed to Descartes the only sound method of discovery. His revolutionary step was to attempt to solve problems in the sciences and philosophy by applying the rules of mathematics. His work, however, is remembered for his development of a method rather than his work in the physical sciences, which is now considered flawed and obsolete.
Descartes initiated a major shift away from Aristotle with the notion that individuals should examine problems for themselves rather than relying on tradition. The four rules for individual inquiry he outlines in Part Two are a summary of the thirty-six rules he intended to publish as Rules for the Direction of the Mind (published posthumously). In essence, the first rule is about avoiding the prejudices that come with age and education. The second rule is a call for breaking every problem into its most basic parts, a practice that signals the shift from the traditional approach to science into an approach more in line with mathematics. The third rule is about working from simple elements to the more complicated elements—what math teachers call “order of operations.” The fourth rule prescribes attention to detail.
Descartes’ imposition of this method on scientific inquiry signals the break between Aristotelian thought and continental rationalism, a philosophical movement that spread across parts of Europe in the seventeenth and eighteenth centuries, of which Descartes is the first exemplar. Aristotelian science, like rationalism, proceeds from first principles that are assumed to be absolutely true. Aristotelians, like Descartes, proceed from those first principles to deduce other truths. However, the principle truths accepted by Aristotelians are less certain than the ones Descartes hopes to establish. By undertaking to doubt everything that cannot be deduced with pure reason, Descartes undermines the Aristotelian method. For centuries, scholars had based their philosophy on sense perception in combination with reason. Descartes’ new philosophy instead proceeds from doubt and the denial of sensory experience.
Continental rationalism held that human reason was the basis of all knowledge. Rationalists claimed that if one began with intuitively understood basic principles, like Descartes’ axioms of geometry, one could deduce the truth about anything. Descartes’ method is now used most often in algebraic proofs, geometry, and physics. The gist of the method is that, when attempting to solve a problem, we have to formulate some sort of equation.
Descartes’ moral rules demonstrate both his distrust of the material world and his confidence in his mind’s ability to overcome it. He has near-absolute faith in his ability to control his own mind and believes that he only needs to change it to change reality. If he wants something he can’t have, he won’t struggle to get it or be miserable about not having it. Instead, he’ll just decide not to want it. Descartes’ resolution to become a spectator rather than an actor in the events of the world around him amounts almost to a renunciation of his physical existence. Long after Descartes, scientific study was governed by the ideal of detached observation advanced by Descartes.
Part Four of Discourse is a precursor to his later work, Meditations on First Philosophy, and the major ideas he provides here—that the self exists because it thinks and that God exists because the self is imperfect and there must be a source for the idea of perfection outside the self—are mere sketches of the detailed explanation he provides in Meditations.