Prima Secundæ, Question 18 — Summa Theologiae
Article 1. Whether every human action is good, or are there evil actions?
Objection 1. It would seem that every human action is good, and that none is evil. For Dionysius says (Div. Nom. iv) that evil acts not, save in virtue of the good. But no evil is done in virtue of the good. Therefore no action is evil.
Objection 2. Further, nothing acts except in so far as it is in act. Now a thing is evil, not according as it is in act, but according as its potentiality is void of act; whereas in so far as its potentiality is perfected by act, it is good, as stated in Metaph. ix, 9. Therefore nothing acts in so far as it is evil, but only according as it is good. Therefore every action is good, and none is evil.
Objection 3. Further, evil cannot be a cause, save accidentally, as Dionysius declares (Div. Nom. iv). But every action has some effect which is proper to it. Therefore no action is evil, but every action is good.
On the contrary, Our Lord said (John 3:20): “Every one that doth evil, hateth the light.” Therefore some actions of man are evil.
I answer that, We must speak of good and evil in actions as of good and evil in things: because such as everything is, such is the act that it produces. Now in things, each one has so much good as it has being: since good and being are convertible, as was stated in the I:5:1; I:5:3. But God alone has the whole plenitude of His Being in a certain unity: whereas every other thing has its proper fulness of being in a certain multiplicity. Wherefore it happens with some things, that they have being in some respect, and yet they are lacking in the fulness of being due to them. Thus the fulness of human being requires a compound of soul and body, having all the powers and instruments of knowledge and movement: wherefore if any man be lacking in any of these, he is lacking in something due to the fulness of his being. So that as much as he has of being, so much has he of goodness: while so far as he is lacking in goodness, and is said to be evil: thus a blind man is possessed of goodness inasmuch as he lives; and of evil, inasmuch as he lacks sight. That, however, which has nothing of being or goodness, could not be said to be either evil or good. But since this same fulness of being is of the very essence of good, if a thing be lacking in its due fulness of being, it is not said to be good simply, but in a certain respect, inasmuch as it is a being; although it can be called a being simply, and a non-being in a certain respect, as was stated in I:5:1 (Reply to Objection 1). We must therefore say that every action has goodness, in so far as it has being; whereas it is lacking in goodness, in so far as it is lacking in something that is due to its fulness of being; and thus it is said to be evil: for instance if it lacks the quantity determined by reason, or its due place, or something of the kind.
Reply to Objection 1. Evil acts in virtue of deficient goodness. For it 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 to Objection 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 to Objection 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.
Article 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.
Objection 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.
Objection 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 (Hosea 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 (Article 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.” And just as, in natural things, the primary evil is when a generated thing does not realize its specific form (for instance, if instead of a man, something else be generated); so the primary evil in moral actions is that which is from the object, for instance, “to take what belongs to another.” And this action is said to be “evil in its genus,” genus here standing for species, just as we apply the term “mankind” to the whole human species.
Reply to Objection 1. Although external things are good in themselves, nevertheless they have not always a due proportion to this or that action. And so, inasmuch as they are considered as objects of such actions, they have not the quality of goodness.
Reply to Objection 2. The object is not the matter “of which” (a thing is made), but the matter “about which” (something is done); and stands in relation to the act as its form, as it were, through giving it its species.
Reply to Objection 3. The object of the human action is not always the object of an active power. For the appetitive power is, in a way, passive; in so far as it is moved by the appetible object; and yet it is a principle of human actions. Nor again have the objects of the active powers always the nature of an effect, but only when they are already transformed: thus food when transformed is the effect of the nutritive power; whereas food before being transformed stands in relation to the nutritive power as the matter about which it exercises its operation. Now since the object is in some way the effect of the active power, it follows that it is the term of its action, and consequently that it gives it its form and species, since movement derives its species from its term. Moreover, although the goodness of an action is not caused by the goodness of its effect, yet an action is said to be good from the fact that it can produce a good effect. Consequently the very proportion of an action to its effect is the measure of its goodness.