 Mackie’s conceptual claim in effect amounts to the claim that our concept of a moral requirement is the concept of an objectively, categorically prescriptive requirement. What does this mean? To say that moral requirements are prescriptive is to say that they tell us how we ought to act, to say that they give us reasons for acting. Thus, to say that something is morally good is to say that we ought to pursue it, that we have reason to pursue it. To say that something is morally bad is to say that we ought not to pursue it, that we have reason not to pursue it. To say that moral requirements are categorically prescriptive is to say that these reasons are categorical in the sense of Kant’s categorical imperatives. The reasons for action that moral requirements furnish are not contingent upon the possession of any desires or wants on the part of the agent to whom they are addressed: I cannot release myself from the requirement imposed by the claim that torturing the innocent is wrong by citing some desire or inclination that I have. This contrasts, for example, with the requirement imposed by the claim that perpetual lateness at work is likely to result in one losing one’s job: I can release myself from the requirement imposed by this claim by citing my desire to lose my job (perhaps because I find it unfulfilling, or whatever). Reasons for action which are contingent in this way on desires and inclinations are furnished by what Kant called hypothetical imperatives.