Kitap 11
4
The complete reality, then, of that which exists potentially, when it is completely real and actual, not qua itself but qua movable, is motion. By qua I mean this. The bronze is potentially a statue; but nevertheless the complete reality of the bronze qua bronze is not motion. To be bronze is not the same as to be a particular potentiality; since if it were absolutely the same by definition the complete reality of the bronze would be a kind of motion; but it is not the same.
5
(This is obvious in the case of contraries; for the potentiality for health and the potentiality for illness are not the same—for if they were, health and illness would be the same too—but the substrate which becomes healthy or ill, whether it is moisture or blood, is one and the same.) And since it is not the same, just as color and visible are not the same, it is the complete reality of the potential qua potential that is motion.
6
It is evident that it is this, and that motion results when the complete reality itself exists, and neither sooner nor later. For everything may sometimes be actual, and sometimes not; e.g. the buildable qua buildable; and the actualization of the buildable qua buildable is the act of building.
