Legal Sets

In this Article, I propose that the practices of legal reasoning and analysis are helpfully understood as being primarily concerned not with rules or propositions, but with sets. This Article develops a formal model of the role of sets in the practices of legal actors in a common-law system defined by a recursive relationship between cases and rules. In doing so, it demonstrates how conceiving of legal doctrines as a universe of discourse comprising (sometimes nested or overlapping) sets of cases can clarify the logical structure that governs marginal cases and help organize the available options for resolving such cases according to their form. While many legal professionals may intuitively navigate this set-theoretic structure, the formal model of that structure has important implications for legal theory.

In particular, it (1) generates a useful account of the relationships among rules, standards, and principles; (2) provides a novel set of tools for understanding the nature of precedent; and (3) illuminates an extra-linguistic dimension to the problem of judicial discretion. On the last point, I argue that discretion is not merely a product of the imperfect relationship between abstractions and reality, or between natural language and the world, but that it is instead an emergent property of the structure of legal practice: a structure composed of sets "all the way down."