René Descartes (IPA: rɛˈne.deˌkɑʁ) (March 31, 1596 - February 11, 1650), also known as Cartesius, was a philosopher and mathematician. While most notable for his groundbreaking work in philosophy, he is perhaps best known as the inventor of the Cartesian coordinate system, which was influential upon the development of modern calculus.
He is considered as one of the most important and influential thinkers in human history and is sometimes called the founder of modern philosophy and the Father of Modern Mathematics. He also inspired his contemporaries and following generations of philosophers, leading them to form what we know today as Continental Rationalism, a philosophical position in 17th and 18th century Europe.
He was born in La Haye, Indre-et-Loire, France and at the age of eight he entered the Jesuit College at La Fleche and after graduation studied law at the University of Poitiers, graduating in 1616. He never practiced law, however; in 1618 he entered the service of Prince Maurice of Nassau, leader of the United Provinces of the Netherlands, with the intention of following a military career. He lived in Holland for 20 years where he wrote his first books starting from a short treatise on metaphysics which was not published.
Often regarded as the first "modern" thinker for providing a philosophical framework for the natural sciences as these began to develop, in his Meditations on First Philosophy, Descartes attempts to arrive at a fundamental set of principles that can be known as true without any doubt. To achieve this, he employs a method called Methodological Skepticism: he supposes that any idea which can be doubted is false.
He gives the example of dreaming: in a dream, one's senses perceive things that seem to be real, but do not actually exist. Thus, the data of the senses cannot be relied upon to be necessarily true. Or, perhaps there is an "evil genius": a supremely powerful and cunning being who sets out to try to deceive Descartes from knowing the true nature of reality. Given these possibilities, what is it that one can know for certain?
Initially, Descartes arrives at only a single principle: if I am being deceived, then surely "I" must exist. Most famously, this is known as cogito ergo sum, ("I think, therefore I am") --- although these words do not appear in the Meditations.
Therefore, Descartes concludes that he can be certain that he exists. But in what form? You perceive your body through the use of the senses; however, these have previously been shown to be unreliable. So Descartes concludes that at this point, he can only say that he is a thinking thing.
To further demonstrate the limitations of the senses, Descartes proceeds with what is known as the Wax Argument. He considers a piece of wax: his senses inform him that it has certain characteristics, such as shape, texture, size, color, smell, and so forth. However, when he brings the wax towards a flame, these characteristics change completely. However, it seems that it is still the same thing: it is still a piece of wax, even though the data of the senses inform him that all of its characteristics are different. Therefore, in order properly to grasp the nature of the wax, he cannot use the senses: he must use his mind. Descartes concludes:
"Thus what I thought I had seen with my eyes, I actually grasped solely with the faculty of judgement, which is in my mind."
Thus, Descartes proceeds to construct a system of knowledge, discarding perception as unreliable and instead admitting only deduction as a method. Halfway through the Meditations he also claims to prove the existence of a benevolent God, who, being benevolent, has provided him with a working mind and sensory system, and who cannot desire to deceive him, and thus, finally, he establishes the possibility of acquiring knowledge about the world based on deduction and perception.
In Mathematics, Descartes is considered of utmost importance for his discovery of analytic geometry. Up to Descartes's times, geometry, dealing with lines and shapes, and algebra, dealing with numbers, were regarded as completely different subsets of mathematics. Descartes showed how (almost) all problems in geometry could be translated into problems in algebra, by regarding them as questions asking for the length of a line segment, and using a Coordinate system to describe the problem.
Descartes's theory provided the basis for the Calculus of Newton and Leibniz, and thus for much of modern mathematics. This is even more astounding when one keeps in mind that the work was just meant as an example to his Discours de la méthode pour bien conduire sa raison, et chercher la verité dans les sciences (Discourse on the Method to Rightly Conduct the Reason and Search for the Truth in Sciences, known better under the shortened title Discours de la méthode).
In 1667, after his death, the Roman Catholic Church placed his works on the Index of Prohibited Books.
René Descartes died of pneumonia on February 11, 1650 in Stockholm, Sweden, where he had been invited as a teacher for Queen Christina of Sweden. Accustomed to working in bed till noon, the demands of early morning study by Christina may have had a detrimental effect on his health. Later, his remains were taken to France from Sweden and buried in the Church of St. Genevieve-du-Mont in Paris.
During the French Revolution, his remains were disinterred for burial in The Panthéon, among the great French thinkers. The village in the Loire Valley where he was born was renamed, La Haye - Descartes.