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.