This paper criticizes two accounts of the normativity of practical principles: the empiricist account and the rationalist or realist account. It argues against the empiricist view, focusing on the Humean texts that are usually taken to be its locus classicus. It then argues both against the dogmatic rationalist view, and for the Kantian view, through a discussion of Kant's own remarks about instrumental rationality in the second section of the Groundwork. It further argues that the instrumental principle cannot stand alone. (...) Unless there are normative principles directing us to the adoption of certain ends, there can be no requirement to take the means to our ends. The familiar view that the instrumental principle is the only requirement of practical reason is incoherent. (shrink)