Let’s now turn to Kant’s explanation of the normative authority of  hypothetical imperatives.  While Kant presents a complicated and  intricate argument to explain the normative authority of the categorical  imperative, he claims that hypothetical imperatives require “no special  discussion,” and spends comparatively little time discussing them  (4:417).  Kant’s approach here—which might seem to play into the hands of  instrumentalists (see §4.1 above) who, while  skeptical of the rational authority of the categorical imperative,  follow Kant in thinking that the authority of hypothetical imperatives  is obvious and unproblematic—has been challenged.  Although the “ought”  of a hypothetical imperative is contingent on an agent’s ends, that  “ought” still needs to be explained.  Additionally, it’s not clear that a  hypothetical “ought” is any more compatible with a naturalistic  worldview than a categorical one.  Specifically, some of the same  metaethical challenges that have been raised about the status of the  categorical “ought” could be raised about normative claims in general,  including the hypothetical “ought”  (Hampton 1998, Ch. 4; Shafer-Landau  2006, §6).