In public policy analysis, much confusion exists about the roles of explanation and prescription. To offer a new perspective, a paradigm is developed that gives both theoretical and empirical meaning to the constitutional determination of political preference functions or public sector governance structures. Current policies are viewed as a rational outcome of a political-economic process. Three relevant spaces are specified: result, policy instrument, and constitutional. For the policy instrument space, the paradigm provides a framework for generating testable propositions on government behavior, while, for the constitutional space, the framework is prescriptive. The collective-choice rules of the constitutional space structure the tradeoff between public and special interests.