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.