Shall, Must, May: The Logic of Legal Obligation and Permission


  • Ben Russell



This article seeks to place legal drafting into a structured, logical system. It divides legal sentences into those which confer obligation or permission (called "performatives"), and those which describe obligation or permission (called "deontic declaratives"). It adopts George Coode's views as to the grammatical form of performatives. It then attempts to classify the logical relations between the various types of sentences. The relation holding between deontic declaratives is the traditional relation of "entailment"; the relation holding between performatives is a new relation the author calls "covering". In the case of performatives that impose obligations ("imperatives"), covering relations mirror entailment relations. The situation is more complicated for performatives that grant permission ("permissives"). The author attempts to analyze permissives in terms of providing defences to claims. He finds that covering relations between permissives do not mirror entailment relations. To this, and to confusions between performatives and declaratives, the author attributes various "paradoxes of permission." The author observes that the results of inconsistent drafting are "quandaries" in which a person is both obliged to perform an act and is prohibited from performing it. Despite current trends toward plain language drafting, the author endorses Coode's view that logical analysis is the key to improving legal drafting.