This article tackles the issue of whether and how Hugo Grotius conceives of custom as a formal source of the law of nations. The main claim of it is that not only custom plays a fundamental role in Grotius’s thought, but that his reflections mark a fundamental turning point for the history of customary international law. A crucial role in this process of re-conceptualization is played by Grotius’s reading of Dio Chrysostom, whose oration On custom provides him with an integrated account of custom as a ‘normative practice’ based on rhetorical judgment (as opposed to the Scholastic interpretation of custom as reiteration of voluntary acts). Consequently, I argue that Dio Chrysostom’s text helps Grotius to transpose the question of the normative legitimacy of custom from a moral to an interpretative level. To conclude, I will show that Grotius adopts two different rhetorical strategies to prove the existence of customary norms of ius gentium.

本文解决了雨果·格罗蒂乌斯是否以及如何将习惯视为国家法律的正式渊源的问题。它的主要主张是，习俗不仅在格罗蒂乌斯的思想中起着根本性的作用，而且他的反思标志着习惯国际法历史的根本转折点。在重新概念化的过程的一个关键角色由迪奥金口，他致辞的格劳秀斯的阅读起到定制根据修辞判断为他提供了一种作为“规范性实践”的习俗的综合说明（与学术界将习俗解释为重申自愿行为相反）。因此，我认为Dio Chrysostom的案文帮助Grotius将习俗的规范合法性问题从道德层面转移到了解释层面。总而言之，我将证明格罗蒂乌斯采取了两种不同的修辞策略来证明ius gentium习惯规范的存在。