I answer that, Each thing receives its species in respect of an act and not in respect of potentiality; wherefore things composed of matter and form are established in their respective species by their own forms. And this is also to be observed in proper movements. For since movements are, in a way, divided into action and passion, each of these receives its species from an act; action indeed from the act which is the principle of acting, and passion from the act which is the terminus of the movement. Wherefore heating, as an action, is nothing else than a certain movement proceeding from heat, while heating as a passion is nothing else than a movement towards heat: and it is the definition that shows the specific nature. And either way, human acts, whether they be considered as actions, or as passions, receive their species from the end. For human acts can be considered in both ways, since man moves himself, and is moved by himself. Now it has been stated above (1) that acts are called human, inasmuch as they proceed from a deliberate will. Now the object of the will is the good and the end. And hence it is clear that the principle of human acts, in so far as they are human, is the end. In like manner it is their terminus: for the human act terminates at that which the will intends as the end; thus in natural agents the form of the thing generated is conformed to the form of the generator. And since, as Ambrose says (Prolog. super Luc.) "morality is said properly of man," moral acts properly speaking receive their species from the end, for moral acts are the same as human acts.