Principles of Philosophy is a book by René Descartes. In essence it is 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.