|Born||March 31, 1596 (La Haye en Touraine [now Descartes], Indre-et-Loire, France)|
|Died||February 11 1650, Stockholm|
|Founded||The Modern Scientific Method, Modern Mathematics|
|Contributed to||Philosophy of Mind, Mathematics, Cartesianism, Rationalism, Foundationalism, Metaphysics, Epistemology, Science|
|influenced by||Plato, Aristotle, Anselm, Aquinas, Ockham, Suarez, Mersenne, Sextus Empiricus, Michel de Montaigne|
|influenced||Isaac Newton, Spinoza, Hobbes, Arnauld, Malebranche, Pascal, Locke, Leibniz, More, Kant, Husserl|
René Descartes (March 31, 1596 – February 11, 1650), also known as Cartesius, was a noted French philosopher, mathematician, and scientist. The "Founder of Modern Philosophy" and the "Father of Modern Mathematics", he is one of the most important and influential thinkers of modern times. His scientific method inspired others to doubt everything and to discard old knowledge to build new knowledge.
Empiricists criticised aspects of his rationalism. This culminated in Kant's Critique of Pure Reason. The critique towards mind-body dualism came mostly later, and in Descartes Error by professor Damasio.
Attempting something new
Descartes often tried to begin to write his topics "as if no one had written on these matters before". Many elements of his philosophy have precedents in late aristotelianism, the revived atoicism of the 16th century and 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.
Rationalism vs empiricism
Descartes was a major figure in 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, and Hume.
Descartes' reflections on mind and mechanism inspired western thought much later, impelled by the invention of the electronic computer and by the possibility of machine intelligence. His most famous statement is Cogito ergo sum (French: Je pense, donc je suis or in English: I think, therefore I am), found in §7 of Principles of Philosophy (Latin) and part IV of Discourse on Method (French).
Descartes sees that he can think of himself as a thinking entity without a body, but he cannot imagine a non-thinking body to be himself. Therefore he concluded "...that I was a substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent on any material thing; so that " I," that is to say, the mind by which I am what I am, is wholly distinct from the body". This mind-body dualism made it easier for him to analyze body and mind separately. In the 20th century, this was the most criticized idea of his, since the idea that the mind is somehow the function of brain became widespread.
Descartes described animals and the human body as machines, but the mind seemed to him to have no parts that he could find. He suggested that the mind and the body might be connected via the pineal gland.
Descartes was born in La Haye en Touraine (now Descartes), Indre-et-Loire, France on March 31, 1596. When he was one year old, his mother died of tuberculosis. His father was a judge in the High Court at Justice. 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, in accordance with his father's wishes that he become a lawyer.
Descartes never practised law, however, and in 1618 he entered the service of Prince Maurice of Nassau, leader of the United Provinces of the Netherlands as a soldier. His intention was to see the world and to discover the truth. He wrote that the exercise kept him healthy.
- "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, particularly the problem of fall of heavy bodies. 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. He arrived in La Haye in 1623, selling all of his property, investing this remuneration in bonds which provided Descartes with a comfortable income for the rest of his life. 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.
Although Descartes never married, he fathered a daughter, the issue of an affair with a woman named Helene; Francine, born in 1635 and baptized on August 7 of the same year. Much to Descartes' distress, 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 Utrecht University, 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.
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. Others believe that Descartes may have contracted pneumonia as result of nursing a French ambassador, ill with aforementioned disease, back to health.  However, letters to and from the doctor Eike Pies have recently been discovered which indicate that Descartes may have been poisoned using arsenic.
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 Sainte-Geneviève-du-Mont in Paris. His 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. His tomb is in Saint-Germain-des-Prés' church in Paris.
The two most well known are Discourse on Method and Meditations.
Discourse on Method
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).
Note; Descartes was also sceptical of memory, as that has also been known to be manipulated, and can be doubted, so the 'cogito' argument can only apply to the present. The phrase is therefore more accurately (but less famously) translated as; "I am thinking, therefore I exist"
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. Descartes defines "thought" (cogitatio) as "what happens in me such that I am immediately conscious of it, insofar as I am conscious of it". Thinking is thus every activity of a person of which he is immeditately conscious.
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 (through both the ontological argument and trademark argument). 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.
In Descartes' system, knowledge takes the form of ideas, and philosophical investigation is the contemplation of these ideas. This concept would influence subsequent internalist movements as Descartes' epistemology requires that a connection made by conscious awareness will distinguish knowledge from falsity. As a result of his Cartesian doubt, he sought for knowledge to be "incapable of being destroyed", in order to construct an unshakeable ground from which all other knowledge can be based on. The first item of unshakeable knowledge that Descartes argues for is the aforementioned cogito, or thinking thing.
Descartes also wrote a response to skepticism about the existence of the external world. He argues that sensory perceptions come to him involuntarily, and are not willed by him. They are external to his senses, and according to Descartes, this is evidence of the existence of something outside of his mind, and thus, an external world. Descartes goes on to show that the things in the external world are material by arguing that since God would not deceive him as to the ideas that are being transmitted, and that God has given him the "propensity" to believe that such ideas are caused by material things. Sceptics have responded to Descartes' proof for the external world by positing a brain in a vat thought experiment, in that Descartes' brain may be connected up to a machine which simulates all of these perceptions.
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' rule of signs is also a commonly used method in modern mathematics to determine possible quantities of positive and negative zeros of a function.
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°). 
- (1911) Encyclopedia Britannica.
- Gullberg, Jan (1997). Mathematics From The Birth Of Numbers. W. W. Norton. ISBN 0-393-04002-X.
- Tipler, P. A. and G. Mosca (2004). Physics For Scientists And Engineers. W. H. Freeman. ISBN 0-7167-4389-2.