Reply Obj. 1:  Evil acts in virtue of deficient goodness.  For if there were nothing of good there, there would be neither being nor possibility of action.  On the other hand if good were not deficient, there would be no evil.  Consequently the action done is a deficient good, which is good in a certain respect, but simply evil.

Reply Obj. 2:  Nothing hinders a thing from being in act in a certain respect, so that it can act; and in a certain respect deficient in act, so as to cause a deficient act.  Thus a blind man has in act the power of walking, whereby he is able to walk; but inasmuch as he is deprived of sight he suffers a defect in walking by stumbling when he walks.

Reply Obj. 3:  An evil action can have a proper effect, according to the goodness and being that it has.  Thus adultery is the cause of human generation, inasmuch as it implies union of male and female, but not inasmuch as it lacks the order of reason. ________________________

SECOND ARTICLE [I-II, Q. 18, Art. 2]

Whether the Good or Evil of a Man’s Action Is Derived from Its Object?

Objection 1:  It would seem that the good or evil of an action is not derived from its object.  For the object of any action is a thing.  But “evil is not in things, but in the sinner’s use of them,” as Augustine says (De Doctr.  Christ. iii, 12).  Therefore the good or evil of a human action is not derived from their object.

Obj. 2:  Further, the object is compared to the action as its matter.  But the goodness of a thing is not from its matter, but rather from the form, which is an act.  Therefore good and evil in actions is not derived from their object.

Obj. 3:  Further, the object of an active power is compared to the action as effect to cause.  But the goodness of a cause does not depend on its effect; rather is it the reverse.  Therefore good or evil in actions is not derived from their object.

On the contrary, It is written (Osee 9:10):  “They became abominable as those things which they loved.”  Now man becomes abominable to God on account of the malice of his action.  Therefore the malice of his action is according to the evil objects that man loves.  And the same applies to the goodness of his action.

I answer that, as stated above (A. 1) the good or evil of an action, as of other things, depends on its fulness of being or its lack of that fulness.  Now the first thing that belongs to the fulness of being seems to be that which gives a thing its species.  And just as a natural thing has its species from its form, so an action has its species from its object, as movement from its term.  And therefore just as the primary goodness of a natural thing is derived from its form, which gives it its species, so the primary goodness of a moral action is derived from its suitable object:  hence some call such an action “good in its genus”; for instance, “to make use of what is one’s own.”