French theologian, controversialist, and moralist. He formed a close friendship with A. Arnauld, in collaboration with whom many of his works were written, including the Logique ou l'Art de penser (commonly known as the Logique de Port-Royal, 1662). A number of his works deal with the Jansenist controversy, but they are more moderate in tone than most Jansenist works. He also wrote against the Calvinists and the Quietists. His main work, the Essais de morale (1671–8), reflected his pessimistic view of fallen humanity and generally advocated both outward and inward withdrawal from the world, though he accepted that those with positions in the world could live a serious Christian life.