While Henry Sidgwick may be best known as a moral philosopher and the author of The Methods of Ethics (1874), he made notable contributions spanning economics and other fields as well, one of them being The Principles of Political Economy (1883). Even now The Methods and its treatment of utilitarianism is recognized as an authoritative model for ethical theory, but his conclusion that there is a “dualism of practical reason” has generated a great deal of controversy. The relationship between these two works has not yet been fully analyzed in the scholarly and critical literature. In this paper I demonstrate that the structure of the argument in The Principles is closely related to The Methods . Sidgwick distinguishes economics as a Science (what is) from economics as an Art (what ought to be) based on two moral principles, egoism and utilitarianism, both explicated in The Methods . Sidgwick's Science/Art distinction is instantiated by his distinction between “economic man” and “ordinary man.” Economic man is an abstraction signifying economic behavior based on self-interest. In Sidgwick's argument, Science can employ the idea of economic man to objectively analyze a society where self-interested economic behavior is the norm. Ordinary man, on the other hand, is the ideal of economic behavior motivated by moral rules based on both self-interest and utilitarianism. Art defines those governmental activities desired in a society consisting of “ordinary men.” Self-interested economic activity does not necessarily achieve the preferred results. When it leads to monopoly, for example, it works to reduce social production. The dilemma of Sidgwick's “dualism of practical reason” is the generation of conflict between the outcome of economic man's behavior and the desired results of behavior by ordinary man. As I attempt to show here, in The Principles Sidgwick constructed a role for government that would resolve that problem. Furthermore, using the distinction between Science and Art, and introducing egoism and utilitarianism, Sidgwick tried to resuscitate the ideas of the classical school of political economy.