French philosopher, 1596-1650, author of Discours de la Méthode, Traité des passions de l'âme, Meditationes de prima philosophia, Principia philosophiae and other works
Fishburn and Hughes: "A celebrated French philosopher, regarded as the father of modern philosophy, whose method, enunciated in his Discours de la méthode (1637), is based on the principle that no statement is valid until proved to be so. Starting from a condition of total doubt, Descartes arrives at the initial proposition that, in order to doubt, one has to think and therefore to exist:'dubito, ergo cogito, ergo sum.' His methodological principle is that anything which we 'perceive clearly and distinctly' must exist. Since we think of God, the perfect being, he must exist, for such an idea could not originate from our imperfect nature unless it had been implanted there by God. Moreover the very nature of perfection involves, among other attributes, that of existence, which proves the existence of God: the Ontological Argument. Being perfection, God cannot deceive us; therefore we must believe any phenomenon true to which our consciousness testifies with clarity and distinctness: this implies that the world also exists. Descartes believed in the dualism of spirit and substance which he held to be reconcilable only through the influence of God.
Pierre Menard, Author of the Quixote: Descartes made a notable contribution to geometry, showing how geometrical problems could be resolved in algebraic terms. He proposed that this same method could be used to set out all existing knowledge systematically, in universally understandable symbols, which would lead to a universal language, a project that interested many other philosophers, such as Wilkins and Leibniz." (60)