René Descartes (March 31, 1596 -- February 11, 1650)
"I think, therefore I am."
Descartes, also known as Cartesius, was a noted French philosopher, mathematician, and scientist. He was one of the most influential thinkers of the Scientific Revolution in the West. As the inventor of the Cartesian coordinate system, he is regarded as the founder analytic geometry, the bridge between algebra and geometry which was crucial to the invention of calculus by Newton and Leibniz. The Cartesian plane in which any point is described by a unique ordered pair (x, y) is fundamental to analytical geometry.
He introduced the now common notation for algebraic equations, in which the first letters of the alphabet represent constant coefficients and the last letters represent variables. For example, the quadratic equation:
a·x2 + b·x + c = 0.
He also introduced the present day notation for repeated multiplication (raising to a power):
3×3×3×3 is written as 34.
His most famous philosophical work dealt with the concept of 'existence'. In his investigation of reality, there was one thing he never doubted -- that he existed; "I think, therefore I am." Thought proves existence of the thinker. He then argues that a perfect God exists, and since that God would not deceive his created beings, the things we experience around us must also be real.
Descartes believed that all material bodies, including the human body, are machines that operate by mechanical principles. In his physiological studies, he dissected animal bodies to show how their parts move. He argued that, because animals have no souls, they do not think or feel; thus vivisection, which Descartes pioneered, is permissible. This was controversial even in his day; many Christians were aghast at Descartes' apparent treatment of animals as nothing more than machines. Henry More, the highly regarded Cambridge Platonist, attacked Descartes in a 1648 letter "with the internecine and cutthroat idea that you advance in the [Discourse on] Method, which snatches life and sensibility away from all the animals..." In his Metaphysical Colloquy of 1641 Pierre Gassendi, a Roman Catholic priest, ridiculed Descartes' illogical inconsistencies with regard to the rationality and sentience of animals.
Writings by Descartes include: Compendium Musica (1618), Rules for the Direction of the Mind (1628), Discourse on Method (1637), La Géométrie (1637), Meditations on First Philosophy (1641), Principles of Philosophy (1644), The Singing Epitaph (1646), Comments on a Certain Broadsheet (1647), The Description of the Human Body (1647), Conversation with Burman (1648), Passions of the Soul (1649).