What then is movement? While belonging to a subject, it is something by itself before belonging to a subject, as are quality, quantity, and being. To begin with, nothing is predicated before it, and of it, as a genus. Is change[417] anterior to movement? Here change is identical with movement, or if change is to be considered a genus, it will form a genus to be added to those already recognized. Besides, it is evident that, on this hypothesis, movement will become a species, and to it will be opposed, as another species, "generation," as, for instance, "generation" is a change, but not a movement.[418] Why then should generation not be a movement? Is it because what is generated does not yet exist, and because movement could not exist in non-being? Consequently, neither will generation be a change. Or is this so because generation is an alteration and increase, and because it presupposes that certain things are altered, and increase? To speak thus is to busy ourselves with things that precede generation. Generation presupposes production of some other form; for generation does not consist in an alteration passively undergone, such as being warmed, or being whitened; such effects could be produced before realization of the generation. What then occurs in generation? There is alteration. Generation consists in the production of an animal or plant, in the reception of a form. Change is much more reasonably to be considered a species, than movement; because the word change means that one thing takes the place of another, while movement signifies the actualization by which a being passes from what is proper to it, to what is not, as in the translation from one place to another. If that be not admitted (to define movement), it will at least have to be acknowledged that the action of studying it, as that of playing the lyre, and in general, all the movements that modify a habit, would be subsumed within our definition. Alteration therefore could not be anything else but a species of movement; since it is a movement which produces passage from one state to another.[419] DEFINITION OF ALTERATION. 22. Granting that alteration is the same thing as movement, so far as the result of movement is to render something other than it was, (we still have to ask) what then is movement? To indulge in a figurative expression,[343] it is the passage of potentiality to the actualization of which it is the potentiality.[420] MOVEMENT AS A FORM OF POWER.