ABSTRACTThe question of how common usage could be constitutive for the meaning of linguistic expressions has been discussed by Renaissance philosophers such as Lorenzo Valla, and it also played an important role in Renaissance theories of juridical interpretation. An aspect of the analysis of common usage in Renaissance theories of juridical interpretation that concerns the role of presumption has not yet found much attention. Renaissance jurists such as Simone de Praetis, Nicolaus Everardus, and Aimone de Cravetta saw that both the usage of Latin by practitioners of law and the vernacular common usage of ordinary people often differed from the technical definition of legal concepts as laid down by ancient jurists or modern legislators. In some cases, they ascribed both to Latin and to vernacular common usage the power of changing the meaning of juridical terms. Still, they were aware of the fact that matters of common usage involve always a degree of uncertainty. The methodological notion of presumption is one of the concepts that figured most prominently in Renaissance approaches to the problem of uncertainty, and, in particular, it was applied in the analysis of meaning-change of legal concepts through common usage.