PETER SYLVAIN, a French philosopher, and a great propagator of the doctrines of Descartes, was born in Agenois in the year 1632. He studied languages and philosophy under the Jesuits at Cahors; and as his views were then directed to the church, he was afterwards occupied in the study of divinity at the university of that town. His progress in learning was so uncommon, that at the end of four years he was offered a doctor's degree without the usual charges; but he did not think it became him to accept of it till he had also studied in the Sorbonne at Paris. He went thither, but was soon disgusted with theology; and as the philosophy of Descartes began at that time to make a noise, in consequence of the lectures of Rohault, he conceived a taste for, and gave himself up entirely to, the study of it. He frequented these lectures; and becoming an adept, went to Toulouse in 1665, and read lectures himself. Having fine parts, a clear and fluent manner, and a happy way of making himself understood, he attracted all sorts of people; the magistrates, the learned, the ecclesiastics, and the very women, who now all affected to abjure the ancient philosophy. In 1680 he returned to Paris, where the concourse which flocked to him was such that the sticklers for the peripatetic philosophy began to be alarmed. They applied to the Archbishop of Paris, who thought it expedient, in the name of the king, to put a stop to the lectures, which accordingly were discontinued for several months. The whole life of Regis was spent in propagating the new philosophy. In 1690 he published a formal system thereof, containing logic, metaphysics, physics, and morals, in three volumes 4to, written in French. It was reprinted the year after, at Amsterdam, with the addition of a discourse upon ancient and modern philosophy. He wrote afterwards several pieces in defence of his system, in which he had disputes with M. Huet, Duhamel, Malebranche, and others. His works, though abounding with ingenuity and learning, have been disregarded, in consequence of the great discoveries and advancement in philosophical knowledge which have since been made. He had been chosen member of the Academy of Sciences in 1699, and he died in 1707.

Besides his System of Philosophy, he wrote the following works: The Use of Reason and of Faith; an Answer to Huet's Censures of the Cartesian Philosophy; an Answer to Duhamel's Critical Reflections; some pieces against Malebranche, to show that the apparent magnitude of an object depends solely on the magnitude of its image traced upon the retina; and a small piece upon the question, Whether Pleasure constitutes our present Happiness?