Reply Obj. 3:  The conjugal act and adultery, as compared to reason, differ specifically and have effects specifically different; because the other deserves praise and reward, the other, blame and punishment.  But as compared to the generative power, they do not differ in species; and thus they have one specific effect.

Reply Obj. 4:  A circumstance is sometimes taken as the essential difference of the object, as compared to reason; and then it can specify a moral act.  And it must needs be so whenever a circumstance transforms an action from good to evil; for a circumstance would not make an action evil, except through being repugnant to reason. ________________________

SIXTH ARTICLE [I-II, Q. 18, Art. 6]

Whether an Action Has the Species of Good or Evil from Its End?

Objection 1:  It would seem that the good and evil which are from the end do not diversify the species of actions.  For actions derive their species from the object.  But the end is altogether apart from the object.  Therefore the good and evil which are from the end do not diversify the species of an action.

Obj. 2:  Further, that which is accidental does not constitute the species, as stated above (A. 5).  But it is accidental to an action to be ordained to some particular end; for instance, to give alms from vainglory.  Therefore actions are not diversified as to species, according to the good and evil which are from the end.

Obj. 3:  Further, acts that differ in species, can be ordained to the same end:  thus to the end of vainglory, actions of various virtues and vices can be ordained.  Therefore the good and evil which are taken from the end, do not diversify the species of action.

On the contrary, It has been shown above (Q. 1, A. 3) that human actions derive their species from the end.  Therefore good and evil in respect of the end diversify the species of actions.

I answer that, Certain actions are called human, inasmuch as they are voluntary, as stated above (Q. 1, A. 1).  Now, in a voluntary action, there is a twofold action, viz. the interior action of the will, and the external action:  and each of these actions has its object.  The end is properly the object of the interior act of the will:  while the object of the external action, is that on which the action is brought to bear.  Therefore just as the external action takes its species from the object on which it bears; so the interior act of the will takes its species from the end, as from its own proper object.

Now that which is on the part of the will is formal in regard to that which is on the part of the external action:  because the will uses the limbs to act as instruments; nor have external actions any measure of morality, save in so far as they are voluntary.  Consequently the species of a human act is considered formally with regard to the end, but materially with regard to the object of the external action.  Hence the Philosopher says (Ethic. v, 2) that “he who steals that he may commit adultery, is strictly speaking, more adulterer than thief.”