The doctrine of precedent, as it has evolved within the common law, has at its heart a form of reasoning—broadly speaking, a logic—according to which the decisions of earlier courts in particular cases somehow generalize to constrain the decisions of later courts facing different cases, while still allowing these later courts a degree of freedom in responding to fresh circumstances. Although the techniques for arguing on the basis of precedent are taught early on in law schools, mastered with relative ease, and applied on a daily basis by legal practitioners, it has proved to be considerably more difficult to arrive at a theoretical understanding of the doctrine itself, a clear articulation of the underlying logic. My purpose in this paper is to describe a new framework within which we can begin to address this problem. I concentrate on two of the most fundamental questions in the theory of precedent. First, how is it, exactly, that precedent cases constrain future decisions—what is the mechanism of constraint? And second, how is a balance then achieved between the constraints of precedent and the freedoms allowed to later courts for developing the law. The view I present will be contrasted with three other views, or models, of precedential constraint appearing in the literature. The first is the rule model. A precedent case normally contains, not only a description of the facts of the case along with a decision on the basis of those facts, but also some particular rule through which that decision was reached. According to the rule model, it is this rule that carries the precedential constraint. Constraint by precedent just is constraint by rules; a precedent case constrains the decision of a later court when the rule contained in that precedent applies to the fact situation confronting the later court.