Louis De Thomassin, a French theologian, born in Aix, Provence, Aug. 28, 1619, died in Paris, Dec. 24, 1695. He studied in the college of Marseilles, became a member of the French Oratory, was appointed to the chair of philosophy in the college of Pezenas, where he adopted Platonic principles, and taught dogmatic theology for six years at Saumur. From 1654 to 1667 he was professor of dogma in the seminary of St. Magloire, Paris, also delivering lectures on church history and discipline. He seemed at first to favor the opinions of the Jansenists, but soon declared against them. In 1667 he published Dissertationes in Concilia Generalia et Particularia, in which he taught that to the pope alone belongs the right of assembling general councils; that these councils are not in themselves necessary; that in all matters of discipline and government the authority of the pope is superior to that of a general council; that the question of papal infallibility should never be discussed, but that it was " sufficient to hold that the pope is greater than himself when at the head of a council, and a council inferior to itself when separated from the pope." These opinions aroused the hostility of the parliament and of the Gallican portion of the clergy, and the regent suppressed the work.

His most important works are : Memoires sur la grace (3 vols. 8vo, 1668; 2 vols. 4to, 1682); Ancienne et nouvelle discipline de l'Eglise touchant les benefices et les benefciers (3 vols, fol, 1678-9; translated into Latin by the author, 1688, 1728); Dogmata Theologica (3 vols, fol., 1680-'89; 6 vols., 1864-'9); Traite de l'unite de l'Eglise et des moyens que les princes Chretiens ont employes pour y faire rentrer ceux qui en etaient separes (1686-'8); and Traite des edits et autres moyens spiri-tuels et temporels dont on s'est servi dans tous les temps pour etablir et pour maintenir l'unite de l'Eglise catholique (3 vols. 4to, 1703).