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. The book sets 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, it is still generally referred to as Newton's First Law of Motion. The book was primarily intended to replace the Aristotelian curriculum then used in French and British universities. The work provides a systematic statement of his metaphysics and natural philosophy, and represents the first truly comprehensive, mechanistic account of the universe. Preface to the French edition Descartes asked Abbot Claude Picot to translate his Latin Principia Philosophiae into French. For this edition, he wrote a preface disguised as a letter to the translator, whose title is "Letter of the author to the translator of the book, that may be used as a preface." This was published in 1647, a date already in the mature, final period of his life. In this writing, Descartes pours some reflexions about his idea of wisdom and philosophy. Its content may be summarized as follows. Concept of philosophy Philosophy is the study of wisdom, understood as the ability to conduct the human activities; and also as the perfect knowledge of all the things that a man can know for the direction of his life, maintenance of his health, and knowledge of the arts. Only God is perfectly wise, and the man is more or less wise, in proportion to the knowledge he has of the most important truths. The degrees of knowledge Descartes identifies four degrees of knowledge, he names common, and a fifth one he designates as higher. The first degree consists on clear and evident notions that can be acquired without need of any meditation. The second degree is all that is learned by means of the senses. The third comprises what we learn when talking with other men. The fourth consists on what we can learn from the