  This line of thought can be traced back to the philosophy of David Hume, who famously asserted that ‘Reason is, and ought only to be the slave of the passions’ (Hume 1978, 415). Those attracted to the Humean approach should bear in mind, however, that instrumental rationality is itself the expression of an objective normative commitment. The instrumental principle says that we are rationally required to take the means that are necessary to achieve our ends; if the principle represents a binding norm of practical reason, then we are open to rational criticism to the extent we fail to exhibit this kind of instrumental consistency, regardless of whether we want to comply with the principle or not.  If naturalism really entails that there can be no objective norms or values, it may be wondered how an exception can possibly be made for the instrumental requirement. A more consistently naturalistic position would be to reject even Zweckrationalität in favor of a skeptical attitude towards practical reason in all its forms (Hampton 1998)—an attitude that may well correspond to the intentions of the historical Hume (compare Dreier 1997, Millgram 1995).  Further questions can be raised about the plausibility of the suggestion that the instrumental norm exhausts the requirements of practical reason. The norm says that one should take the means that are necessary relative to one’s psychologically-given ends. But how can the fact that a given means exhibits this kind of necessity give a person reason to choose the means, if the end is not itself something it would be valuable to achieve in some way? The instrumental principle seems to function as a binding norm of practical reason only if it is taken for granted that there are additional, independent standards for the assessment of our ends (Korsgaard 1997; Quinn 1993).