 How, specifically, does Kant think that one can establish the categorical imperative a priori? The crucial premise is that practically rational beings are autonomous, in the sense that their wills can be determined by rules they give themselves. Kant holds that the law that an autonomous agent gives to herself must tell her which ends to pursue and not merely which means to employ in light of the ends the agent already has. Kant therefore rejects the more orthodox conception of practical reason as purely instrumental, i.e., limited to discovering the means to ends dictated by something else, e.g., desire. The question then becomes, “What rule or law could determine the rational will apart from any end?” that is, “What rule could possibly tell a rational agent which ends to pursue?” Such a rule would have to be formal, since it could not simply tell the agent what to do in light of the ends she already has, and thus could not include any specification of an end. This leads Kant to the categorical imperative, roughly: for an agent to perform a moral action, the maxim the agent acts on must be one that the agent can consistently will to govern everyone, regardless of their goals, as a necessary law.