Objection 1. It would seem that a circumstance cannot place a moral action in the species of good or evil. For the species of an action is taken from its object. But circumstances differ from the object. Therefore circumstances do not give an action its species.
Objection 2. Further, circumstances are as accidents in relation to the moral action, as stated above (Question 7, Article 1). But an accident does not constitute the species. Therefore a circumstance does not constitute a species of good or evil.
Objection 3. Further, one thing is not in several species. But one action has several circumstances. Therefore a circumstance does not place a moral action in a species of good or evil.
On the contrary, Place is a circumstance. But place makes a moral action to be in a certain species of evil; for theft of a thing from a holy place is a sacrilege. Therefore a circumstance makes a moral action to be specifically good or bad.
I answer that, Just as the species of natural things are constituted by their natural forms, so the species of moral actions are constituted by forms as conceived by the reason, as is evident from what was said above (Article 5). But since nature is determinate to one thing, nor can a process of nature go on to infinity, there must needs be some ultimate form, giving a specific difference, after which no further specific difference is possible. Hence it is that in natural things, that which is accidental to a thing, cannot be taken as a difference constituting the species. But the process of reason is not fixed to one particular term, for at any point it can still proceed further. And consequently that which, in one action, is taken as a circumstance added to the object that specifies the action, can again be taken by the directing reason, as the principal condition of the object that determines the action's species. Thus to appropriate another's property is specified by reason of the property being "another's," and in this respect it is placed in the species of theft; and if we consider that action also in its bearing on place or time, then this will be an additional circumstance. But since the reason can direct as to place, time, and the like, it may happen that the condition as to place, in relation to the object, is considered as being in disaccord with reason: for instance, reason forbids damage to be done to a holy place. Consequently to steal from a holy place has an additional repugnance to the order of reason. And thus place, which was first of all considered as a circumstance, is considered here as the principal condition of the object, and as itself repugnant to reason. And in this way, whenever a circumstance has a special relation to reason, either for or against, it must needs specify the moral action whether good or bad.
Reply to Objection 1. A circumstance, in so far as it specifies an action, is considered as a condition of the object, as stated above, and as being, as it were, a specific difference thereof.
Reply to Objection 2. A circumstance, so long as it is but a circumstance, does not specify an action, since thus it is a mere accident: but when it becomes a principal condition of the object, then it does specify the action.
Reply to Objection 3. 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. Nevertheless there is no reason why one action should not be in several, even disparate, moral species, as said above (07, ad 1; 1, 3, ad 3).
Source: Summa Theologica (New Advent)