Analyses are given of the concepts of absolute and prima facie obligation. The former is a maximizing analysis: roughly, one ought absolutely to perform those actions which are performed in the best worlds accessible to one. The latter analysis is roughly this: one ought prima facie to perform those actions which are such that those accessible worlds in which they are performed are better than the closest accessible worlds in which they are not performed. Accounts of conditional obligation, both absolute (...) and prima facie, are also given, and the issue of the detachment of unconditional from conditional obligation is addressed. (shrink)