St. Peter tells us in his letter that no man can do evil to bring about good. This is a moral compass by which we can judge our acts. Now, according to Aquinas there are a lot of things that make up a human act. Different people parse them out slightly differently but generally we can say the following:
Pertaining to the Will:
- The Object
- The Agent
For our purposes the way in which they are all categorized is irrelevant. What is essential, however, is that we analyze an act based on these parts of an act. Now, according to Aquinas, if any one of these parts is objectively evil then the whole act is objectively evil. This is the judgement of the act itself. There are only good acts or evil acts.
Now, according to the question of the “OP” it is necessary to see that his question is not about the act but rather it is about the praise or blame conferred upon an agent for the act that they bring into use. This is a very different question than about the nature of act itself. This has to do, not with the objective aspect of the act but with the subjective. In other words, it is about judging if the person acted rightly or wrongly in a particular circumstance. Now, there is a further principle and that is: No objectively evil act can ever be good. What this means is that there is no level of ignorance or mitigation of culpability that can cause an objectively evil act to somehow become good in this particular circumstance. Rather, the mitigating circumstances will make the culpability of the agent less but most likely it will never full wipe it out completely.
So, let’s take a concrete example:
- A person performs an act of fornication.
- Fornication is an objectively evil act.
- This person performed an evil act = true.
So, now we ca say that we have identified that the person did something bad. Now the question is about praise or blame. In this case there can be no praise because of the above principle that an objectively evil act cannot ever be judged to be a good act. So we ask the question:
- Is there a reason for thinking that the persons responsibility is mitigated?
- If no, then full blame.
- If yes, then partial blame.
So, given the position of Aquinas there is no way for, say, lying, even to a bad person or institution, to ever be a good. However, given the previous example of hiding people and lying to persecutors of those people the evil is mitigated – but according to Aquinas it is still an evil act because of the objective status of the act itself, which is evil.