The Principles of Philosophy

Principles of Philosophy (Principia philosophiae) is a book by René Descartes. It is basically a synthesis of the Discourse on Method and Meditations on First Philosophy It was written in Latin, published in 1644 and dedicated to Elisabeth of Bohemia, with whom Descartes had a long standing friendship. A French version (Les Principes de la Philosophie) followed in 1647. It set forth the principles of nature—the Laws of Physics--as Descartes viewed them. Most notably, it set forth the principle that in the absence of external forces, an object's motion will be uniform and in a straight line. Newton borrowed this principle from Descartes and included it in his own Principia; to this day, we refer to it as Newton's First Law of Motion.