Supererogation, dual-role views, and the logic of reasons

Intuitively, one can do more than morality requires. Thus, you seem to do more than morality requires---in jargon, you supererogate---when you knowingly let grave harm come to you to save a stranger's life. But while supererogation is part and parcel of our commonsense morality, it is also a puzzling phenomenon. Among other things, it gives rise to three puzzles. This paper develops a formal system, or logic, that resolves these three puzzles. The system emerges once we combine a well-known defeasible logic that has been used to model the way reasons relate to requirements with the core insight of dual-role views of reasons, or views that say, roughly, that while normative reasons can play two different roles in determining all-things-considered statuses of acts, they need not always play both of them. The unified solution to the puzzles that the system supports has several advantages over related informal solutions.