The International Court of Justice (ICJ) regularly invokes a two-element test for the identification of customary international law: state practice accompanied by opinio juris. Yet the Court’s application of this test has appeared inconsistent. In some cases, an absence of evidence of opinio juris leads to a finding that an alleged rule of customary international law does not exist; yet in other cases, there is no clear evidence of opinio juris on the part of states participating in the practice, but the Court nevertheless concludes that the alleged customary rule exists. In other cases, the Court concludes that a customary rule exists apparently based on evidence of opinio juris alone. This article argues that these judgments do not undermine the ICJ’s claim to be applying a two-element analysis but reveal something fundamental about how customary international law is identified – namely, that how the existence of state practice and opinio juris is evaluated may vary depending on the nature of the customary rule under investigation (for example, whether it is a permissive or prohibitive rule) and the context of underlying international law rules in which that alleged new customary international law rule is located.

中文翻译：

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规则的性质和背景与习惯国际法的识别

国际法院 (ICJ) 经常援引一项两要素检验来识别习惯国际法：国家实践与法律确信。然而，法院对该测试的应用似乎不一致。在某些情况下，缺乏法律确信证据会导致认定所称的习惯国际法规则不存在；然而在其他案件中，没有明确证据表明参与该做法的国家有法律确信，但法院仍然得出结论认为所称的习惯规则存在。在其他案件中，法院得出结论认为，显然存在仅基于法律确信的证据的习惯规则。