Obj. 3:  Further, acts that differ in species produce different effects.  But the same specific effect results from a good and from an evil action:  thus a man is born of adulterous or of lawful wedlock.  Therefore good and evil actions do not differ in species.

Obj. 4:  Further, actions are sometimes said to be good or bad from a circumstance, as stated above (A. 3).  But since a circumstance is an accident, it does not give an action its species.  Therefore human actions do not differ in species on account of their goodness or malice.

On the contrary, According to the Philosopher (Ethic ii. 1) “like habits produce like actions.”  But a good and a bad habit differ in species, as liberality and prodigality.  Therefore also good and bad actions differ in species.

I answer that, Every action derives its species from its object, as stated above (A. 2).  Hence it follows that a difference of object causes a difference of species in actions.  Now, it must be observed that a difference of objects causes a difference of species in actions, according as the latter are referred to one active principle, which does not cause a difference in actions, according as they are referred to another active principle.  Because nothing accidental constitutes a species, but only that which is essential; and a difference of object may be essential in reference to one active principle, and accidental in reference to another.  Thus to know color and to know sound, differ essentially in reference to sense, but not in reference to the intellect.

Now in human actions, good and evil are predicated in reference to the reason; because as Dionysius says (Div.  Nom. iv), “the good of man is to be in accordance with reason,” and evil is “to be against reason.”  For that is good for a thing which suits it in regard to its form; and evil, that which is against the order of its form.  It is therefore evident that the difference of good and evil considered in reference to the object is an essential difference in relation to reason; that is to say, according as the object is suitable or unsuitable to reason.  Now certain actions are called human or moral, inasmuch as they proceed from the reason.  Consequently it is evident that good and evil diversify the species in human actions; since essential differences cause a difference of species.

Reply Obj. 1:  Even in natural things, good and evil, inasmuch as something is according to nature, and something against nature, diversify the natural species; for a dead body and a living body are not of the same species.  In like manner, good, inasmuch as it is in accord with reason, and evil, inasmuch as it is against reason, inasmuch as it is against reason, diversify the moral species.

Reply Obj. 2:  Evil implies privation, not absolute, but affecting some potentiality.  For an action is said to be evil in its species, not because it has no object at all; but because it has an object in disaccord with reason, for instance, to appropriate another’s property.  Wherefore in so far as the object is something positive, it can constitute the species of an evil act.