The uses of the outputs of the International Law Commission in international adjudication: subsidiary means or artefacts of rules?

This paper examines the methods which international courts and tribunals (ICTs) employ when using ILC outputs for the purpose of determining rules of international law and their content. Specifically, it identifies common patterns in the ways in which ICTs, first, justify their reliance on ILC outputs and, second, deal with their ambiguities. The paper argues in favour of a consistent methodology for the treatment of ILC outputs in international adjudication. Such a framework is based on the distinction between the identification of the status of a normative proposition contained in these texts and the determination of its content or its interpretation. The identification of the status of a normative proposition requires a critical assessment and reconstruction of the evidence leading up to its development taking also into account that these instruments are not a monolith from the perspective of sources. However, the interpretation of a proposition whose status is uncontested follows a line of inquiry akin to treaty interpretation. This observation has broader implications for the process of interpretation in international law. Specifically, apart from the context of treaty interpretation, international courts or tribunals interpret the normative propositions contained in ILC outputs as a methodological shortcut for the interpretation of rules of customary international law or general principles of law. Conversely, the employment of methods akin to treaty interpretation in this context can constitute evidence of the emergence of common rules, principles, or good practices of interpretation that are also applicable to unwritten international law.