for leaving France. But even in Holland he became involved in controversies, because both Protestant and Roman Catholic theologians regarded his philosophy with suspicion. At the invitation of Queen Christina he spent his last years in Sweden.
1. Descartes, who was a great mathematician himself (founder of Analytical Geometry), attributed the distinction between geometry and philosophy to the fact that the former is based upon principles concerning which there could be no room for doubt, whilst the controversies in philosophy pertain to these very principles. The discovery and establishment of first principles require the use of the analytic method, i.e. we must proceed from the given or the provisionally established to its presuppositions. Analysis finally leads to simple intuitions, and these in turn originate directly through experience. The subjective movements of intellect are of this sort, e.g. that a triangle is bounded by three lines—that a thing cannot both be and not be at the same time,—that everything has a cause, —that the effect cannot be greater than its cause,—that I must exist if I think (Régles pour la direction de l’esprit, evidently written 1628-1629). He called these processes simple intuitions, and afterwards made the last one mentioned the basis of his theory (in the Discours and in the Meditationes which appeared in 1641). It is possible to doubt every idea or object of knowledge; all our perceptions or postulates might be illusory. But doubt has a definite limit. Even the most radical doubt presupposes thought. Thought is a reality even though all of its conclusions should be illusory. Descartes takes the word thought in its broadest sense: thought is everything which goes on in consciousness. When, in the language of his famous proposition, he says: Je pense, donc je suis!