  Among the substantive norms of practical reason, those of instrumental rationality have seemed least controversial to philosophers.  Instrumental rationality, in its most basic form, instructs agents to take those means that are necessary in relation to their given ends.  In the modern era, this form of rationality has widely been viewed as the single unproblematic requirement of practical reason. The instrumental principle makes no assumptions about the prospects for rational scrutiny of peoples’ ends.  Rational criticism of this kind apparently presupposes that there are objective reasons and values, providing standards for assessment of ends that are independent from psychological facts about what people happen to be motivated to pursue. In line with the naturalistic attitude sketched in section 2, however, it may be doubted whether such independent standards can be reconciled with the metaphysical commitments of contemporary scientific practice. A world that is shorn of objective values or norms leaves no room for rational criticism of peoples’ ends, but only for Weberian Zweckrationalität: the rational determination of means to the realization of ends that are taken to be given, as a matter of human psychological fact.