 Positions on the eternity of the world by some masters of arts were in some cases very provocative. In the eyes of Siger of Brabant, the natural philosopher cannot but conclude that the world is eternally created, whereas the metaphysician concedes that God’s will is inscrutable and that hence there is no certainty about eternity or non-eternity (De aeternitate mundi; Quaest. in tertium De anima q.2). For Boethius of Dacia, the natural philosopher has to infer the eternity of movement from the principles of natural philosophy, but the metaphysician, even though he can demonstrate the existence of a first cause, is unable to demonstrate whether the world is coeternal with the first cause or non-eternal, given the inscrutability of God’s will (De aeternitate mundi). Both authors share the conviction that the natural philosopher is forced to conclude that the world is eternal, thus provoking theological opposition. The arguments for this conclusion were largely furnished by Arabic sources.