Rene Descartes --Great Minds, Great Thinkers

On November 10, 1619, René Descartes has the dream that inspires his "Meditations on First Philosophy". From the article:

"René Descartes (March 31, 1596 - February 11, 1650), also known as Cartesius, worked as a philosopher and mathematician. While most notable for his groundbreaking work in philosophy, he has achieved wide fame as the inventor of the Cartesian coordinate system, which influenced the development of modern calculus.
Descartes, sometimes called the founder of modern philosophy and the Father of Modern Mathematics, ranks as one of the most important and influential thinkers in human history. 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.

Descartes' Life
Descartes was born in La Haye, Indre-et-Loire, France and at the age of eight entered the Jesuit College at La Fleche (today the Prytanee Militaire de la Fleche). After graduation he studied at the University of Poitiers, graduating with a Baccalauréat and Licence in law in 1616.
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, with the intention of following a military career. Here he met the late Isaac Beeckman, and composed a short treatise on music entitled Compendium Musicae. In 1619, he travelled in Germany, and on November 10 had a vision of a new mathematical and scientific system. In 1622 he returned to France, and during the next few years spent time in Paris and other parts of Europe.

In 1628 he composed Rules for the Direction of the Mind, and left for Holland, where he lived until 1649, changing his address frequently. In 1629 he began work on The World. In 1633, Galileo was condemned and Descartes abandoned plans to publish The World. In 1635, Descartes' daughter Francine was born. She was baptized on August 7, 1635 and died in 1640. Descartes published Discourse on the Method, with Optics, Meteorology and Geometry in 1637. In 1641, Meditations on First Philosophy was published, with the first six sets of Objections and Replies. In 1642 the seond edition of Meditations was published with all seven sets of Objections and Replies, followed by Letter to Dinet. In 1643, Cartesian philosophy was condemned at the University of Utrecht, and Descartes began his long correspondance with Pricess Elizabeth of Bohemia. Descartes published Principles of Philosophy and visited France in 1644. In 1647 he was awarded a pension by the King of France, published Comments on a Certain Broadsheet and began work on Description of the Human Body. He interviewed Frans Burman at Egmond-Binnen in 1648, resulting in Conversation with Burman. In 1649 he went to Sweden on invitation of Queen Christina, and his Passions of the Soul, which he dedicated to Princess Elizabeth, were published.

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, he may have suffered a detrimental effect on his health due to Christina's demands for early morning study. 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.

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

Significance
Often regarded as the first "modern" thinker for providing a philosophical framework for the natural sciences as these began to develop, Descartes in his Meditations on First Philosophy 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 things 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 genius" 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 later wrote them in Discourse on the Method.

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 proven unreliable. So Descartes concludes that at this point, he can only say 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. 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 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 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.

Mathematicians consider Descartes of the utmost importance for his discovery of analytic geometry. Up to Descartes's times, geometry, dealing with lines and shapes, and algebra, dealing with numbers, appeared as completely different subsets of mathematics. Descartes showed how to translate (almost) all problems in geometry 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 appears 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).

A student of Descartes once said 'I don't know what I like, but I know that I art.'"