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 * For other things named Descartes, see Descartes (disambiguation).

René Descartes (IPA:, March 31 1596 – February 11 1650), also known as Cartesius, was a noted French philosopher, mathematician, and scientist. Dubbed the "Founder of Modern Philosophy" and the "Father of Modern Mathematics," he ranks as one of the most important and influential thinkers of modern times. For good or bad, much of subsequent western philosophy is a reaction to his writings, which have been closely studied from his time down to the present day. Descartes was one of the key thinkers of the Scientific Revolution in the Western World. He is also known for inventing the Cartesian coordinate system used in plane geometry and algebra.

Descartes frequently contrasted his views with those of his predecessors. In the opening section of the Passions of the soul, he goes so far as to assert that he will write on his topic "as if no one had written on these matters before". Nevertheless many elements of his philosophy have precedents in late Aristotelianism, the revived Stoicism of the 16th century, or in earlier philosophers like Augustine. In his natural philosophy, he differs from the Schools on two major points: first, he rejects the analysis of corporeal substance into matter and form; second, he rejects any appeal to ends—divine or natural—in explaining natural phenomena. In his theology, he insists on the absolute freedom of God’s act of creation.

Descartes founded 17th century continental rationalism, later advocated by Baruch Spinoza and Gottfried Leibniz, and opposed by the empiricist school of thought, consisting of Hobbes, Locke, Berkeley & Hume. Leibniz, Spinoza and Descartes were all versed in mathematics as well as philosophy, and Descartes and Leibniz contributed significantly to science as well. As the inventor of the Cartesian coordinate system, Descartes founded analytic geometry, that bridge between algebra and geometry crucial to the invention of the calculus and analysis. Descartes's reflections on mind and mechanism began the strain of western thought that much later, impelled by the invention of the electronic computer and by the possibility of machine intelligence, blossomed into, e.g., the Turing test and John Searle's "Chinese room" argument.

His most famous statement is Cogito ergo sum (I think, therefore I am.).

Biography
On March 31, 1596, Descartes was born in La Haye en Touraine, Indre-et-Loire, France. When he was 1 year old, his mother died of tuberculosis. At the age of ten, he entered the Jesuit Collège Royal Henry-Le-Grand at La Flèche. After graduation, he studied at the University of Poitiers, earning a Baccalauréat and Licence in law in 1616.

Descartes never actually practiced law, however, and in 1618 he entered the service of Prince Maurice of Nassau, leader of the United Provinces of the Netherlands. His intention was to see the world and to discover the truth.
 * "I entirely abandoned the study of letters. Resolving to seek no knowledge other than that which could be found in myself or else in the great book of the world, I spent the rest of my youth traveling, visiting courts and armies, mixing with people of diverse temperaments and ranks, gathering various experiences, testing myself in the situations which fortune offered me, and at all times reflecting upon whatever came my way so as to derive some profit from it. (Descartes, Discourse on the Method of Rightly Conducting One's Reason and Seeking the Truth in the Sciences)

Here he met Isaac Beeckman who sparked his interest in mathematics and the new physics. On November 10 1619, while traveling in Germany and thinking about using mathematics to solve problems in physics, Descartes had a vision in a dream through which he "discovered the foundations of a marvelous science." This became a pivotal point in young Descartes' life and the foundation on which he develops analytical geometry. He dedicated the rest of his life to researching this connection between mathematics and nature.

In 1622 he returned to France, and during the next few years spent time in Paris and other parts of Europe. Descartes was present at the siege of La Rochelle by Cardinal Richelieu in 1627. He left for Holland in 1628, where he lived and changed his address frequently until 1649.

In 1633, Galileo was condemned by the Catholic Church, and Descartes abandoned plans to publish Treatise on the World, his work of the previous four years.

Although Descartes never married, he fathered a daughter Francine, born in 1635 and baptized on August 7 of the same year. She died in 1640.

Descartes continued to publish works concerning mathematics and philosophy for the rest of his life. In 1643, Cartesian philosophy was condemned at the University of Utrecht, and Descartes began his long correspondence with Princess Elizabeth of Bohemia. In 1647, he was awarded a pension by the King of France. Descartes was interviewed by Frans Burman at Egmond-Binnen in 1648. In 1649, Descartes went to Sweden on invitation of professor Eitan Olevsky.

René Descartes died on February 11, 1650 in Stockholm, Sweden, where he had been invited as a teacher for Queen Christina of Sweden. The cause of death was said to be pneumonia - accustomed to working in bed till noon, he may have suffered a detrimental effect on his health due to Christina's demands for early morning study. However, letters to and from the doctor Eike Pies have recently been discovered which indicate that Descartes may have been poisoned using arsenic.

In 1667, the Roman Catholic Church placed his works on the Index of Prohibited Books.

As a Catholic in a Protestant nation, he was interred in a graveyard mainly used for unbaptized infants in Adolf Fredrikskyrkan in Stockholm. Later, his remains were taken to France and buried in the Church of St. Genevieve-du-Mont in Paris. A memorial erected in the 18th century remains in the Swedish church.

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 in 1802, which was shortened to "Descartes" in 1967. Currently his tomb is in the church Saint Germain-des-Pres in Paris.

Philosophical legacy
Descartes is often regarded as the first modern thinker to provide a philosophical framework for the natural sciences as these began to develop. In his Meditations on First Philosophy he attempts to arrive at a fundamental set of principles that one can know as true without any doubt. To achieve this, he employs a method called methodological skepticism: he doubts any idea that can be doubted.

He gives the example of dreaming: in a dream, one's senses perceive stimuli that seem real, but do not actually exist. Thus, one cannot rely on the \data of the senses as necessarily true. Or, perhaps an "evil demon" exists: 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 can one 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"). (These words do not appear in the Meditations, although he had written them in his earlier work Discourse on Method).

Therefore, Descartes concludes that he can be certain that he exists. But in what form? He perceives his body through the use of the senses; however, these have previously been proven unreliable. So Descartes concludes that the only undoubtable knowledge is that he is a thinking thing. Thinking is his essence as it is the only thing about him that cannot be doubted.

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. 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 to properly 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 judgment, which is in my mind."

In this manner, 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 offers an ontological proof of a benevolent God. Because God is benevolent, he can have some faith in the account of reality his senses provide him, for God has provided him with a working mind and sensory system and does not desire to deceive him; however, this is a contentious argument, as his very notion of a benevolent God from which he developed this argument is easily subject to the same kind of doubt as his perceptions. From this supposition, however, he finally establishes the possibility of acquiring knowledge about the world based on deduction and perception. In terms of epistemology therefore, he can be said to have contributed such ideas as a rigorous conception of foundationalism and the possibility that reason is the only reliable method of attaining knowledge, as others said before him, though not as clearly as he did, and the rationalist answer to scepticism which other rationalists have elaborated on.

Mathematical legacy
Descartes's theory provided the basis for the calculus of Newton and Leibniz, by applying infinitesimal calculus to the tangent problem, thus permitting the evolution of that branch of modern mathematics. This appears even more astounding considering that the work was just intended 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).

Descartes also made contributions in the field of optics, for instance, he showed by geometrical construction using the Law of Refraction that the angular radius of a rainbow is 42° (i.e. the angle subtended at the eye by the edge of the rainbow and the ray passing from the sun through the rainbow's centre is 42°).

Writings by Descartes

 * 1618. Compendium Musicae. A treatise on music theory and the aesthetics of music written for Descartes' early collaborator Isaac Beeckman.
 * 1626–1628. Regulae ad directionem ingenii (Rules for the Direction of the Mind). Incomplete. First published posthumously in 1684. The best critical edition, which includes an early Dutch translation, is edited by Giovanni Crapulli (The Hague: Martinus Nijhoff, 1966).
 * 1630–1633. Le Monde (The World) and L'Homme (Man). Descartes' first systematic presentation of his natural philosophy. Man was first published in Latin translation in 1662; The World in 1664.
 * 1637. Discours de la méthode (Discourse on Method). An introduction to the Essais, which include the Dioptrique, the Météores and the Géométrie.
 * 1637. La Géométrie (Geometry). Descartes' major work in mathematics. There is an English translation by Michael Mahoney (New York: Dover, 1979).
 * 1641. Meditationes de prima philosophia (Meditations on First Philosophy), also known as Metaphysical Meditations. In Latin; a French translation, probably done without Descartes' supervision, was published in 1647. Includes six Objections and Replies. A second edition, published the following year, included an additional objection and reply, and a Letter to Dinet.
 * 1644. Principia philosophiae (Principles of Philosophy). A Latin textbook at first intended by Descartes to replace the Aristotelian textbooks then used in universities. A French translation, Principes de philosophie by Claude Picot, under the supervision of Descartes, appeared in 1647 with a letter-preface to Queen Christina of Sweden.
 * 1647. Notae in programma (Comments on a Certain Broadsheet). A reply to Descartes' one-time disciple Henricus Regius.
 * 1647. The Description of the Human Body. Published posthumously.
 * 1648. Responsiones Renati Des Cartes… (Conversation with Burman). Notes on a Q&A session between Descartes and Frans Burman on 16 April 1648. Rediscovered in 1895 and published for the first time in 1896. An annotated bilingual edition (Latin with French translation), edited by Jean-Marie Beyssade, was published in 1981 (Paris: PUF).
 * 1649. Les passions de l'âme (Passions of the Soul). Dedicated to Princess Elizabeth of Bohemia.
 * 1657. Correspondance. Published by Descartes' literary executor Claude Clerselier. The third edition, in 1667, was the most complete; Clerselier omitted, however, much of the material pertaining to mathematics.

Trivia

 * It is said that during the 1640s, Descartes travelled with an artificial female companion, named Francine after his daughter. This apocryphal story may stem from his published statements about the nature of the mind, or may indeed have been an early automaton or Gynoid.(Cartesian lore has it that later an exact replica was made from less durable materials, named Dolly and believed to be partially conscious when heard to utter the words: "Where am I?")
 * Descartes was ranked #49 on Michael H. Hart's list of the most influential figures in history.
 * The Descartes Highlands area on the moon, where John Young and Charlie Duke landed on Apollo 16, is named after him. Also contains a mountain range named the Descartes Mountains.
 * Descartes stated that, for a period of his life, he was attracted to cross-eyed women. He cited his attraction as being instilled by a cross-eyed childhood playmate, and said that, once he realized this cause, he was able to rid himself of it. He adduced this as evidence that the human mind can freely control the body.
 * Although Descartes in real life avoided alcoholic overindulgence, he is charged with extreme intoxication ("I drink, therefore I am") in Monty Python's celebrated Philosophers' Song.