A Contrario Arguments

This chapter analyses a contrario (or e contrario) arguments as legal justification techniques that infer normative consequences from what authoritative legal texts do not say, i.e., from legislative silence. Against the traditional distinction between “strong” and “weak” a contrario reasoning, the authors argue that legal practice actually deploys several distinct argumentative operations and therefore propose a more fine-grained typology. They reconstruct two core models: the first model captures the “strong” version of the argument, where the legal provision is interpreted biconditionally and thus implicitly regulates unmentioned cases in the opposite way; the second model captures the interpretive move that the text regulates only the mentioned case and therefore does not determine the unmentioned one. Building on the second model, the chapter distinguishes a minimal a contrario argument (establishing a genuine legal gap) and a weak a contrario argoment (concluding for the default outcome because no sufficient grounds—e.g., by analogy—exist to fill the gap), while also discussing the potential addition of a disanalogy variant. The chapter finally articulate justification conditions for each version and relate a contrario reasoning to interpretive practices and pragmatic assumptions about legislative communication. The chapter is part of a collective research volume that brings together the leading scholars in the theory of legal argumentation.