Authority is not of one kind, and authoritative directives may have different effects on the practical reasoning of their addressees. In this regard, we can distinguish between two types of authority—epistemic and decisionist. Although both are used to influence people’s actions, they diverge in the way in which they are respected and treated by those who follow them. This plurality of forms of authority is closely related to some of the questions that have been bothering legal philosophers for centuries, and particularly to questions concerning the relation between reason and fiat in law. Based on the distinction between epistemic and decisionist modes of reasoning with authoritative directives, we can distinguish two discrete logics governing the dynamics of positive law: an epistemic logic which makes law aspire to correctness and reasonableness, and a decisionist logic which leads to the identification of law with its positive particularity. In the final part of this article, I consider the practical and conceptual implications of this duality.