By the end of the thirteenth century, it was clear that Aristotle’s physics and cosmology presented claims that were incompatible with God’s omnipotence. According to Scotus, “whatever does not evidently include a contradiction and from which a contradiction does not necessarily follow, is possible for God.” But many states of affairs, treated as impossible by Aristotle, seemed to involve no contradiction. Already in 1277, Stephen Tempier, Bishop of Paris, had issued his influential condemnation of, among other things, several key claims of Aristotle’s physics and cosmology precisely because they implied limitations on God’s absolute power. This condemnation did not lead to a wholesale rejection of Aristotelian thought, however. Aristotle had provided the most detailed and powerful conception of the physical universe known to medieval thinkers, and Scotus, like most of his contemporaries, was deeply wedded to this conception in its broad outlines and in a great deal of its detail. But he formed part of a movement, beginning in the late thirteenth century, and gathering momentum in the fourteenth, in which this conception was intensely scrutinized and modified in a number of fundamental respects. Nowhere did Aristotle’s thought pose greater problems than in doctrines concerning space and time. Scotus’s writings were an important chapter in the reexamination and modification of Aristotelian doctrines on these issues.