So, what is Kant’s explanation of the normative authority of hypothetical imperatives?  According to Korsgaard (1997), Kant’s views changed over the course of his philosophical development.  Kant’s early “dogmatic rationalist” view (evident in the Groundwork) held that we should comply with these hypothetical imperatives simply because they express what a perfectly rational agent would do.  But the mature Kantian view—which Korsgaard endorses—explains the normative authority of hypothetical imperatives in terms of the commitments that are constitutive of willing.  According to this view, what’s involved in willing some end (as opposed to merely desiring it) is being committed to taking the means to that end.  It’s not that complying with this commitment is constitutive of intention (this would render instrumental irrationality conceptually impossible) but that having this commitment is constitutive of intention.  So, when one is instrumentally irrational, one fails to live up to one’s own commitments.  Korsgaard writes: