 Epicurus held that the elementary constituents of nature are undifferentiated matter, in the form of discrete, solid and indivisible particles (“atoms”) below the threshold of perception, plus empty space, that is, the complement of matter or where matter is not (Inwood 1981, Konstan 2014; contra Sedley 1982, who argues that space, for Epicurus, is a continuous matrix extending uniformly throughout the universe, and is either occupied by matter or empty). In its broad outline, Epicurus inherited this scheme from the earlier atomists, above all Democritus. But Democritus’ version had been the object of critiques by later thinkers, especially Aristotle, in part for incoherencies in the notion of an infinite void, in part for problems attaching to his idea of minima, or entities of the smallest conceivable size (see especially Physics Book 6). First, freestanding entities of minimal size could have no edges, and so no shapes, or rather would be all edge: thus, if two minima touched, they would wholly overlap. (The same argument applies to points in a line, which is why a line contains points but is not composed of them, according to Aristotle.) Further, if atoms really are conceptually indivisible, and not just physically unsplittable, then when two atoms pass by each other it is impossible that they should at any time be only partway past, for this would imply a point partway along the length of the atom, which contradicts the premise that it is a minimum. Although Aristotle does not state the argument precisely in this form, it is apparent that a strict conception of minimal-sized atoms entails that motion too must consist of discontinuous quanta; and if motion, then time. Atoms must, then, Aristotle inferred, move in discrete hops (kinêmata), each one occupying a single temporal minimum — and hence, all atoms must move at a uniform speed. An infinite void, with atoms distributed throughout it, led to problems of its own, for it permits no intrinsic spatial orientation and hence no account of why things fall, as they are observed to do.