Abstract

Legal theorists agree widely on two necessary and jointly sufficient conditions for the existence of a legal system: a legal system exists if (i) legal officials adopt a critically reflective attitude toward the legal system’s foundational rule, and (ii) the substantive laws of the system are “by and large” efficacious. The latter “efficacy condition” plausibly applies to all posited law, paradigmatically including modern centralized legal systems and less paradigmatic instances like international law. And yet, philosophers have also frequently pointed out the difficulty in determining precisely what this efficacy amounts to. In this article, I argue that the persisting difficulty of explaining the efficacy of law results from three tempting but inadequate assumptions about posited law and that our basic assumptions need to be revised accordingly.