René Descartes was a French philosopher, mathematician, and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day.
"It is some years now since I realized how many false opinions I had accepted as true from childhood onwards, and that, whatever I had since built on such shaky foundations, could only be highly doubtful."
"For to be possessed of a vigorous mind is not enough; the prime requisite is rightly to apply it. The greatest minds, as they are capable of the highest excellences, are open likewise to the greatest aberrations; and those who travel very slowly may yet make far greater progress, provided they keep always to the straight road, than those who, while they run, forsake it."
Descartes believed that matter had no inherent qualities, but was simply the "brute stuff" which occupied space. He divided reality into the res cognitas (consciousness, mind) and res extensa (matter, extension).
At the beginning of Meditation II, reflecting on the evil genius posited at the end of Meditation I, Descartes observes: ‘Let him deceive me as much as he can, he will never bring it about that I am nothing so long as I think that I am something… I must finally conclude that this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind’
Descartes sought to replace “real qualities” with a mechanistic account of qualities in objects. He rendered light as a property of particles and their motions: it is a “tendency to move” as found in a continuous medium and radiating out from a luminous body.
Following on from early movements towards the use of symbolic expressions in mathematics by Diophantus, Al-Khwarizmi and François Viète, "La Géométrie" introduced what has become known as the standard algebraic notation, using lowercase a, b and c for known quantities and x, y and z for unknown quantities.
After an education in the scholastic and humanistic traditions, Descartes’ earliest work was mostly in mathematics and mathematical physics, in which his most important achievements were his analytical geometry and his discovery of the law of refraction in optics.
Descartes presented his results in major works published during his lifetime: the Discourse on the Method (1637), with its essays, the Dioptrics, Meteorology, and Geometry; the Meditations on First Philosophy with its Objections and Replies (1641); the Principles of Philosophy, covering his metaphysics and much of his natural philosophy (1644).
At the heart of Descartes' philosophical method was his refusal to accept the authority of previous philosophers, and even of the evidence of his own senses, and to trust only that which was clearly and distinctly seen to be beyond any doubt (a process often referred to as methodological skepticism or Cartesian doubt or hyperbolic doubt).
French mathematician René Descartes, heralded as the first modern philosopher, believed that science and mathematics could be used to explain everything in nature and was the first to describe the physical universe in terms of matter and motion.