Firstly when one acts one brings something into being: Something is made real through the act of the will. By running I make my intention of going for a run real. The things that are actualized in this world can be good, bad or indifferent.
When one performs a good act one wants to bring something good into the world. When one an evil act they causes an evil in this world. But what happens when one brings about an action which brings about both good and evil at the same time?
How does one form a moral assessment of surgery, in the days prior to anaesthetic? When the knife is put into the flesh, curing the patient (good) begins at the same time pain(evil) and mutilation(evil) is actuated. To deliberately cure someone is good, to deliberately hurt someone is evil, then how do we evaluate the morality of surgery if intrinsic to its actuation, good and evil result?
The Christian tradition stated that the moral species of the act is determined through its moral object: what was the moral quality of the “thing” realized through the act. Example; putting a dent in a brand new car--as in an act of vandalism--is evil, since by denting a car, it is privated in some way. The moral object of an act concerns itself with the moral quality of what is bought about by the act, not why the act was done.
Now according to Aquinas one does good when one actualizes a good, and one sins (peccatum) when one actualizes an evil; now sin in this context is non-pejorative. A man sins and does good when he performs an action with a double effect. So how to determine its permissibility or not?
- That a person may choose to act in a way which results in mixed moral objects provided that the person is choosing the good moral object.
- The mixed moral quality of the act must on balance be good. A proportional assessment of the act has to be made and the result must be in favor of the good. In sum, a net good is achieved by the act.
Now a man is culpable for the things he has control over not for the things he doesn’t. In choosing an act which actuates mixed moral objects, one cannot be blamed if the evil moral object is bought about, not through any choice of the agent. He is inculpable. However if the evil moral object could be avoided in some way then the agent becomes culpable because he has some choice in what type of evil is bought about. No choice, no culpability. There is a double imperative in Christianity: do good and avoid evil.