  Regius attributed his appointment at Utrecht University to his familiarity with and support for Cartesian philosophy, which was acquired initially by reading Descartes’ first book, the Discours de la Méthode … plus la Dioptrique, les Météores et la Géometrie, 1637 (AT, vol. VI). Regius was sympathetic to Cartesian natural philosophy from his initial reading and began to teach it to students, in private lessons, and to dictate notes with a view to publishing his own summary of natural philosophy based on Cartesian principles. This objective was further encouraged when he read a copy of Descartes’ unpublished manuscript, Le Monde (AT, vol.  XI), in 1641. The natural philosophy of Le Monde rejected scholastic forms and qualities as philosophical entities that contributed nothing to an explanation of natural phenomena. There was a significant difference, however, in a university such as Utrecht between not relying on scholastic forms and criticizing them publicly. The transition from the former to the latter, in the case of Regius, occurred in 1641.