Descartes' Discourse on Method and Cogito Ergo Sum

Introduction: Descartes and the Origins of Modern Philosophy

René Descartes is widely recognized as the father of modern philosophy. Also known as Renatus Cartesius — a Latinization of his name — Descartes was a 17th-century French scientist, mathematician, and philosopher. His importance in the history of philosophy is so great because he was among the first to oppose scholastic Aristotelianism, which had influenced European philosophy and culture for almost a thousand years. A French gentleman who signed himself "Lord of Perron" and who spent twenty of his most productive years in the tolerant and hospitable Dutch Republic, Descartes remains a crucial figure in the history of philosophy.

He managed to combine — whether consciously or not — the ideas of the past into a synthesis that was striking in its originality yet congenial to the scientific spirit of the age. Descartes is currently regarded as the progenitor of the modern spirit in philosophy.

Descartes' Philosophical System

Descartes began his philosophical endeavor by methodically doubting knowledge based on authority, the senses, and reason. He remains famous for claiming that "if he thinks, he exists" — a certainty derived from intuition. "Cogito ergo sum" — "I think, therefore I am" — is his most famous statement. His philosophical system was dualistic, drawing a clear distinction between mind, whose essence is thinking, and matter, whose essence is extension in three dimensions. The metaphysical system he developed is based on intuition and derived by reason from innate ideas. Physiology and physics, however, were founded on sensory knowledge, thereby giving them a mechanistic and empiricist character.

Descartes intended to publish a work entitled Le Monde (The World) in 1633, but abandoned the plan when he learned that the Italian astronomer Galileo Galilei had been condemned by the Roman Catholic Church for asserting that the Earth revolves around the Sun. Because the Copernican concept played an essential role in his own work, Descartes suppressed Le Monde, hoping the Church would eventually revise its position and retract Galileo's condemnation.

Although he certainly feared the power of the Church — Giordano Bruno, Nicolaus Copernicus, Galileo Galilei, and others were sobering examples of how the Catholic Church treated innovative thinkers — Descartes also hoped that his physics would one day replace the obsolete Aristotelian conception that had dominated Western culture for centuries. Despite his many merits, Aristotle had exerted a damaging influence on astronomy by asserting that the Earth is the center of the universe, a view that was on the verge of being discarded even in the ancient world.

The Discourse on Method

Descartes published Discours sur la Méthode (Discourse on Method) in 1637. It was one of the first major modern philosophical works not written in Latin, the official scholarly language of the time. Descartes justified his use of French by arguing that all people of good sense — including women, who occupied a lower social status under ancient Roman and medieval traditions — could read his work and learn to employ reason independently. He believed that the natural light of reason was available to everyone, and that any person could use it to distinguish the true from the false.

The method for using reason in the search for scientific truth was debated and illustrated in three essays appended to the Discourse. Dioptrics contained the law of refraction — his dispute with the Dutch physicist Huygens on this topic is well known. Meteorology offered an explanation of the phenomenon of the rainbow, while Geometry presented analytical geometry: a method of representing geometric figures through algebraic equations that made many previously unsolvable problems tractable. Another innovation was the introduction of conventions for representing known numerical quantities with letters such as a, b, c, unknowns with x, y, z, and powers with numerical superscripts (x², x³, etc.). Though they may seem elementary today, these algebraic notations made mathematics far clearer than it had been before.

To analyze the famous "I think, therefore I am" statement fully, one must first understand the foundations of Descartes' philosophy of mind. In the Discourse on Method and in Regulae ad Directionem Ingenii (Rules for the Direction of the Mind), written in 1628 and published posthumously in 1701, Descartes established four rules of reasoning:

"…Just as a multitude of laws often creates excuses for vices, so that the best regulated state is that which, having very few laws, makes those few strictly observed, instead of the great number of precepts which make up logic, I thought that the four following precepts would suffice, provided that I could make a firm, steadfast resolution not to violate them even once."

1) Nothing that is not self-evident should be accepted as truth. "The first was to never accept anything as true which I could not accept as obviously true; that is to say, to carefully avoid impulsiveness and prejudice, and to include nothing in my conclusions but whatever was so clearly presented to my mind that I could have no reason to doubt it."

2) Problems are to be divided into their most simple parts. "The second was to divide each of the problems I was examining into as many parts as I could, as many as should be necessary to solve them."

3) Problems are to be solved by proceeding from simple to complex. "The third, to develop my thoughts in order, beginning with the simplest and easiest to understand matters, in order to reach by degrees, little by little, to the most complex knowledge, assuming an orderliness among them which did not at all naturally seem to follow one from the other."

4) Reasoning should always be rechecked. "And the last resolution was to make my enumerations so complete and my reviews so general that I could be assured that I had not omitted anything."

Descartes' mathematical education clearly influenced him in formulating these rules, which constitute a direct application of algebraic procedures. He also insisted that the key notions and the limits of each problem must be clearly defined:

"I was especially pleased with mathematics because of the certainty and clarity of its proofs; but I did not as yet realize its true usefulness; and, thinking that it was only useful in the mechanical arts, I was astonished that, since its foundations were so firm and solid, no one had built something higher upon it."

These rules of logic were accompanied in the Discourse by a provisional moral code to guide the search for truth: (1) local customs and laws must be obeyed; (2) decisions should be made on the best available evidence and then adhered to firmly; (3) the world cannot be changed as easily as one's desires; (4) truth must always be sought. These provisions reflect the characteristic features of Descartes' moral outlook: conservatism, stoicism, decisiveness, and dedication. Descartes conceived of knowledge as a tree — metaphysics formed the roots, physics the trunk, and medicine, morals, and mechanics the branches that bear the fruits of knowledge.