Supererogation

Driving home from dropping my in-laws at the airport this morning at 4:00, I was thinking about supererogation, that is, acts that are good, but not necessary, actions that are morally above and beyond the call of duty. TheWife and I recently had a discussion about the limits of such actions, when should you say no. Most such acts will cause some degree of inconvenience, but the question is what criterion should you use to determine when the request is over the line. When someone asks something of you that is not required of you, how do you determine whether to say yes or no? Think of helping a friend move. What are the operative factors? Is it a function of your relationship to the person? How long you've known him or her? Whether you may need to ask something of that person later? Is it a matter of how big the favor is or are there some people who could ask the world? Is it a matter of how much you dislike the fumes while painting a friend's house? If some of these are the real reason you say no, are you honest about it? Do you still feel guilty even though it was not a moral requirement? Should you still feel guilty?