 His major work was his "Cours entier de philosophie ou Système général selon les principles de Descartes" (3 vols., Paris, 1690), where he presented in a systematic way the principles of Cartesian philosophy.Opposed to Malebranche's idealism, against which he wrote in the "Journal des Savants" (1693 and 1694), Régis modified the system of Descartes on various points in the direction of empiricism.He denied that the human soul has innate and eternal ideas, maintained that all our ideas are modifications of the soul united to the body and that we can know our body and extension as immediately as our soul and thought.