This paper examines the fundamental problem posed by collective decisions for a social theory based on rational actors each pursuing his own interest. The problem is the absence of consensus about the society's choice, in which case the theory of rational behavior breaks down by failing to predict the outcome. The paper proposes that individuals in social systems are faced with a sequence of social choices, and can thus exchange their partial control over issues that interest them little for greater control of those that interest them more. An ideal or perfect system of collective decisions is defined, in a way analogous to the definition of a perfect market. Finally, the various alternatives to consent are discussed, togeher with some of the considerations that would lead the rational actor to refuse to consent.