Thomas Aquinas

“ It is not every circumstance that places the moral action in the species of good or evil; since not every circumstance implies accord or disaccord with reason. Consequently, although one action may have many circumstances, it does not follow that it is in many species. ”

“ 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. ”

“ Since therefore the difference constitutes the species, it seems that an action is not constituted in a species through being evil. Consequently good and evil do not diversify the species of human actions. ”

“ Nothing hinders an action that is good in one of the way mentioned above, from lacking goodness in another way. And thus it may happen that an action which is good in its species or in its circumstances is ordained to an evil end, or vice versa. ”

“ And every individual action must needs have some circumstance that makes it good or bad, at least in respect of the intention of the end. For since it belongs to the reason to direct; if an action that proceeds from deliberate reason be not directed to the due end, it is, by that fact alone, repugnant to reason, and has the character of evil. ”

“ Therefore, on the other hand, the vicious man, in the matter of each vice, acts when he should not, or where he should not, and so on with the other circumstances. Therefore human actions are good or evil according to circumstances. ”

“ 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. ”

“ Now just as the being of a thing depends on the agent, and the form, so the goodness of a thing depends on its end. Hence in the Divine Persons, Whose goodness does not depend on another, the measure of goodness is not taken from the end. Whereas human actions, and other things, the goodness of which depends on something else, have a measure of goodness from the end on which they depend, besides that goodness which is in them absolutely.
Accordingly a fourfold goodness may be considered in a human action. First, that which, as an action, it derives from its genus ”

“ But no action can be specifically indifferent thus: since no object of human action is such that it cannot be directed to good or evil, either through its end or through a circumstance. Secondly, specific indifference of an action may be due to the fact that as far as its species is concerned, it is neither good nor bad. Wherefore it can be made good or bad by something else. Thus man, as far as his species is concerned, is neither white nor black ”

“ Further, a good action may happen to be ordained to an evil end, as when a man gives an alms from vainglory; and conversely, an evil action may happen to be ordained to a good end, as a theft committed in order to give something to the poor. Therefore an action is not good or evil from its end. ”

“ Further, moral good belongs to virtue, while moral evil belongs to vice. But it happens sometimes that a man fails to ordain a specifically indifferent action to a vicious or virtuous end. Therefore an individual action may happen to be indifferent. ”

“ On the contrary, Our Lord said (Jn. 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 FP, Q [5] , AA [1] ,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. ”

“ 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. ”

“ Every accident is not accidentally in its subject; for some are proper accidents; and of these every art takes notice. And thus it is that the circumstances of actions are considered in the doctrine of morals. ”

“ Since good and being are convertible; according as being is predicated of substance and of accident, so is good predicated of a thing both in respect of its essential being, and in respect of its accidental being ”

“ 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 ”

“ 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. ”

“ 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. ”

“ The other is privation "in process" [privari] : thus sickness is privation of health; not that it takes health away altogether, but that it is a kind of road to the entire loss of health, occasioned by death. And since this sort of privation leaves something, it is not always the immediate contrary of the opposite habit. In this way evil is a privation of good, as Simplicius says in his commentary on the Categories: because it does not take away all good, but leaves some. ”

“ 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 ”