 A typical retort among international lawyers to Hart’s critique is that these are just matters of definition. But this answer misses the distinction between terminological and conceptual disagreement. Hart’s conceptual critique of international law raises crucial questions about its legal character. As Hart himself understood, a failure to conceptualize the social phenomenon that we normally describe as international law does matter, for it hinders both “theoretical enquiries … [and] moral deliberation” (Hart 1961 [2012: 214]). We need to understand what it is that we are talking about if we want to advance moral and political arguments about international law.