Descartes lived from 1596 to 1650, today he is referred to as “the Father of Modern Philosophy.” He created analytical geometry, based on his now immortal Cartesian coordinate system, immortal in the sense that we are all taught it in school, and that it is still up-to-date in all branches of mathematics. Analytical geometry is the study of geometry using algebra and the Cartesian coordinate system.
He discovered the laws of refraction and reflection. He also invented the superscript notation still used today to indicate the powers of exponents. Rene Descartes adhered to the Ontological Argument for the Existence of a Christian God, stating that, because God is benevolent, Descartes can have some faith in the account of reality his senses provide him, for God has provided him with mind and sensory system and does not desire to deceive him.
From this supposition, however, Descartes finally establishes the possibility of acquiring knowledge about the world based on deduction and perception. In terms of the study of knowledge therefore, he can be said to have contributed ideas like a rigorous conception of foundationalism (basic beliefs) and the possibility that reason is the only reliable method of attaining knowledge.
He resigned his commission in the spring of 1621, and spent the next five years in travel, during most of which time he continued to study pure mathematics. In 1626 we find him settled at Paris, ``a little well-built figure, modestly clad in green taffety, and only wearing sword and feather in token of his quality as a gentleman.'' During the first two years there he interested himself in general society, and spent his leisure in the construction of optical instruments; but these pursuits were merely the relaxations of one who failed to find in philosophy that theory of the universe which he was convinced finally awaited him.
He also advocated dualism, which is very basically defined as the power of the mind over the body: strength is derived by ignoring the weaknesses of the human physique and relying on the infinite power of the human mind. Descartes’s most famous statement is the motto of existentialism: “Je pense donc je suis;” “Cogito, ergo sum;” “I think, therefore I am.” This is not meant to prove the existence of one’s body. Quite the opposite, it is meant to prove the existence of one’s mind. He rejected perception as unreliable, and considered deduction the only reliable method for examining, proving and disproving anything.
Descartes last work Les Passions de l'áme was written as a result of the correspondence which Descartes carried on with Princess Elisabeth of Bohemia. The work was written in French, and published in Amsterdam and Paris in 1649. This work (like the Principles) is composed of a large number of short articles.
Princess Elisabeth had raised the question of how the soul could interact with the body in 1643. In response to Elisabeth's questions, Descartes wrote a short work which developed into the Passions of the Soul. The work is a combination of psychology, physiology and ethics, and contains Descartes' theory of two way causal interaction via the pineal gland.
Two months before the publication of the Passions Descartes set sail for Stockholm, Sweden, at the invitation of Queen Christina of Sweden. Descartes' death in Stockholm of pneumonia, has regularly been attributed to the rigours of the Swedish climate and the fact that Descartes (no early riser) was sometimes required to give the Queen lessons as early as five in the morning. However unpleasant these conditions may have been, it seems plain that Descartes acquired his fatal malady as a result of nursing his friend the French ambassador (who had pneumonia) back to health.
René Descartes died on 11 February 1650 in Stockholm, Sweden.