Descartes teaching astronomy to Queen Christina of Sweden. Ren矇 Descartes (1596 - 1650) was a French mathematician, philosopher and scientist. He is considered the father of modern Western philosophy, propounding a rationalist metaphysics as a rejection of the scholastic tradition. His best known philosophical statement, "cogito, ergo sum" ("I think, therefore I am"), is Descartes' expression of belief in the intuition of ones own reality, a concept that laid the foundation for 17th century rationalism. Descartes died in 1650, at the age of 53, soon after becoming tutor to queen Christina of Sweden. The cause of death was said to be pneumonia. Christina (December 18,1626 - April 19, 1689) was queen regnant of Sweden from 1632 to 1654.