What Came First: The Obligation or the Belief? A Renaissance of Consensus Theory to Make the Normative Foundations of Customary International Law More Tangible

Abstract

This article draws on the paradox of the two-element approach to the emergence of customary international law (CIL), as many have done so before. How can a State, acting in a certain way, be convinced of its legal obligation to behave in that manner, if this particular act has not yet been established as CIL, but is solely in the process of emerging? By stepping out of CIL theory and looking at similar conundrums, this article finds that consensus theory is the most prominent candidate for providing a solution. Against the common view, the argument offered here suggests that the most obvious flaws of this explanation are, actually, its greatest strengths. In brief, this understanding enables us to see Article 38 ICJ Statute as a means for identifying the final CIL norm, which is to be distinguished from its formal source. An unwritten meta-norm, as the argument goes, guides the process of CIL emergence. This meta-norm is the correct place to discuss what practice and opinio iuris must look like to count as making an offer and accepting that offer so as to finally give rise to a CIL norm. Consensus theory, thus, teaches us that we need to state more clearly how to evince State practice with its accompanying legal conviction, a task which could and should be addressed by the International Law Commission. Based on this understanding, this article aims to propose a formula grounded in theory to guide the genesis of CIL. Clearly, asking for more specific rules guiding the emergence and succinct identification of State practice and opinio iuris undermines the fluidity and dynamics of CIL. However, it is consensus theory that teaches us that legal certainty has its price.

Keywords: Customary International Law, Two-Elements Approach, Opinio Iuris Paradox, Consensus Theory, Article 38 ICJ Statute, Legal Theory, International Law Commission, Sources of International Law