The forms that utilitarianism took before Sidgwick were almost invariably empiricist and naturalist. To such positions, Sidgwick poses a challenge similar to, but ultimately deeper than, Moore’s more famous charge that such positions inevitably commit a “naturalistic fallacy.” In Sidgwick’s version, empiricist-naturalist theories that attempt to understand ethical concepts and properties in empirical-natural terms all fail to account for their normativity. That can be done, Sidgwick argues, only by recognizing that all ethical judgments contain “the fundamental notion represented by the word ‘ought.’” Sidgwick holds, against Mill and his empiricist predecessors like Hutcheson, that the method of ethics must be “intuitive” rather than “inductive,” in Mill’s terms. Sidgwick’s intuitionism is not, however, the sort that Mill most ardently opposes; it is a “philosophical intuitionism,” by contrast with the complacent commonsense intuitions that Mill seeks to reform with his inductive utilitarianism. This is where Sidgwick’s “dualism of practical reason” comes in. Sidgwick holds that there are two potentially conflicting ultimate rational intuitions: (a) the “axiom of Prudence,” which counsels agents to pursue their own greatest good and (b) the “axiom of Rational Benevolence.” And both of these are hedonistic, yielding rational egoistic hedonism and hedonistic utilitarianism, respectively.