die). In recent years the problem of moral dilemmas has received the attention of a number of philosophers. Some authors1 argue that moral dilemmas are not conceptually possible (i.e., that they are incoherent, given the nature of the concepts involved) because they are ruled out by certain valid principles of deontic logic. Other authors2 insist that moral dilemmas are conceptually possible, and argue that therefore the principles of deontic logic that rule them out must be rejected. In arguing for or against the conceptual possibility of moral dilemmas authors have been almost exclusively concerned with obligation dilemmas, i.e., situations in which more than one action is obligatory. Almost no one has been explicitly concerned with prohibition dilemmas, i.e., situations in which no feasible action is permissible.3 I shall argue that the two types of dilemmas are distinct, and that a much stronger case can be made against the conceptual possibility of obligation dilemmas than against the conceptual possibility of prohibition dilemmas.