Fantastical Opinio Juris and How to Find It

[Moisés Montiel Mogollón is a lawyer advising individuals, companies, and States on matters of international law, human rights, and other international areas at Lotus Soluciones Legales. He teaches Treaty Law and LOAC at Universidad Iberoamericana (Mexico City) and Universidad Panamericana (Guadalajara). Twitter: @moisesmontielm]

Opinio juris remains, to date, the most controversial part in the law governing sources of international law. No one dares question that its verification is necessary for a customary rule to exist. One would, nevertheless, be hard-pressed to convey how such conviction of legality/obligation/necessity/acceptance is evidenced. This piece aims to point out some of the difficulties associated with extracting expressing unambiguous articulations of opinio juris while highlighting a recent development that provides the perfect data sample for analysis: the recent Arria Formula on Self Defense against Non-State Actors in the territory of a third State without its consent.

Opinio Juris and the Customary Hallows

François Gény pointed out more than a century ago that the sole repetition of an act would be undistinguishable from what we call the mores of the people lest the psychological valuation could be established and the motivation of the conduct can be ascertained conclusively. This concurrent test is modernly dubbed the two-element test for determining customary international law. The conventional wisdom is that both constituent elements must be satisfied beyond doubt in order to find ourselves in the presence of customary international law (see para. 77 and also comment 4 to Conclusion 2 of the ILC Draft Conclusions on the subject).

The ILC has acknowledged that the process for the identification of customary international law is not always susceptible to exact formulations. It is suspected that where the Commission wrote “not always”, it actually meant “almost never”. This is further shown when the Commission calls for contextualized evaluation and consideration of the subject matter the rule is said to regulate. Far from clarifying, this complicates the determination. Alas, the ILC is hardly to blame for this. Article 38(1)(b) of the ICJ Statute is tremendously unhelpful in that it only points out the constituent elements of custom and cannot be read in the context of a larger defining instrument (like the Vienna Convention on the Law of Treaties’ article 2(1)(a) regarding the definition of what a treaty within its scope is). An equivalent would be saying that a cake is butter, flour, sugar, eggs, and milk. It’s not wrong; but it adds nothing to the conceptual framework and hinders any attempt at identifying how to bake the coveted delicacy.

Opinio Juris and the Chamber of Inconsistencies

The foremost victim (or perpetrator?) of methodological indeterminacy is the beloved World Court. The bench has been unsuccessful in its attempts to coherently identify opinio juris. In the Anglo-Norwegian Fisheries Case, it deemed silence to be expressive of acceptance, conversely, in the Asylum Case, it held that silence could not mean acceptance. In the Gulf of Maine Case it proposed that inductive reasoning could be used to ascertain the existence of custom, a conclusion later supported by the Jurisdictional Immunities of the State case. In North Sea Continental Shelf case, the dissenters actually used deductive reasoning, as did the majority in the Arrest Warrant case. The dissonance grows with each case decided concerning custom. As Talmon argues, it kind of just pulls customary rabbits out of the proverbial hat without a satisfactory explanation as to where the rule came from, how the bench was assured of its existence, or if separate tests for the constituent elements were made.

The latter has, in turn, caused more confusion over which practices are, in fact and in law, customary. While the preclusion of generating stare decisis is explicit in article 59 of the Statute, the unwarranted attribution of quasi-normative or fully normative value to jurisprudence is something built into lawyers’ mental programming. For example, when speaking about the customary nature of asylum in the Latin American context it would be extraordinary to find a single person who would not go for the Haya de la Torre case. It is, after all, the way that law is taught and the way we are trained to think about it.

To date, the most helpful -even if not fully authoritative- insight into how to determine opinio juris is offered by the ILC’s Draft Conclusions. Conclusion 10 claims that some of the forms of evidence can be -but are not limited to- “public statements made on behalf of States (à la Nuclear Tests Case?); official publications; government legal opinions; diplomatic correspondence; decisions of national courts (if they mean to uphold custom and not domestic law, like in the Banco Nacional de Cuba v Sabbatino Case); treaty provisions (expressive of opinio juris conventionalis); and conduct in connection with resolutions adopted by an international organization (like the “instant” customary law governing extraterrestrial space before its codification) or at an intergovernmental conference”, and even silence under certain circumstances.

In spite of this, it is still almost impossible to discern intent of a sufficient entity in any of these means as to identify a standalone instance of opinio juris. How, then, can it be argued that the reason for acting in any of the above suggested ways is to show that States understand a practice to be normative?. International law being what it is makes it difficult to ascertain that the motive behind any legally relevant articulation is solely or explicitly the articulation of a belief of normativity.

Opinio Juris and the Half-blood Solution

In this regard the first of the vehicles detected by the ILC -subject of Commentary 4 to the 10^th Conclusion- goes on to say that an “express public statement on behalf of a State that a given practice is permitted, prohibited, or mandated under customary international law provides the clearest indication that the State has avoided or undertaken such practice (or recognized that it was rightfully undertaken or avoided by others) out of a sense of legal right or obligation”. The question ensues, why and where would States issue such statements to that express end?

Such an exercise has, in fact, recently occurred. One whose sole purpose was to exchange views on the legality of self-defense practices and where States expressed articulations of legality to the effect of claiming that their preferred views constitute custom. This is highly reminiscing of Johnstone’s proposition of justificatory discourse in the context of interpretative communities, except that here the legal dressage of politically-driven arguments is expressed as a direct function of the legal views of participants about the subject and provide, therefore, clear articulations on the juridical views of States concerning the legality of it (rather than the political convenience or the military/geopolitical necessity of it).

This happened at the Arria Formula meeting convened on February 24^th of this year to discuss whether article 51 of the UN Charter permits self-defense against non-state actors on the territory of a third State without its consent (for the substance of it and an apt summary of positions, see professor Haque’s piece) It should be noted that the quid of the discussion was whether the Charter (in and of itself expressive of customary rules predating it) allows extra-jurisdictional self-defense. This could be seen as an instance of subsequent agreement or ulterior practice (in the broadest sense the VCLT allows), but seeing as the Charter norms on use of force are simultaneously conventional and customary, this opportunity seems too good pass up on.

Quite literally, States gathered in the context of the UN Security Council (even if not a normative instance per se it speaks as to the authority commanded by statements therein made) to opine on whether the practice of extraterritorial self-defense against non-State actors absent consent of the territorial State was permitted or not by article 51 of the UNC. In prospecting for opinio juris a richer vein could not be found: States used legal justificatory discourse, expressed their own legal views, and weren’t coy on articulating what they thought was the definitive meaning, extent, and significance on the customary rules purportedly expanding (or not) self-defense. This seems to be the indicative of certainty about the articulation of legality that opinio juris calls for, it also fulfills and exceeds the threshold suggested by the ICL and would provide a helpful example of what to look for when ascertaining opinio juris for the ICJ.

Additionally, this proposition by Mexico seems to have been welcomed by Member States as a positive development and is, hopefully, likely to be replicated in the future. This would go on to solidify the use of Arria-formula meetings (and international for a in general but in a more much specific and deliberate way) as a perfect vehicle for determining opinio juris with recourse to the method stated in Conclusion 10 of the ILC’s report. Traditionally, droplets of articulations of normativity can be found here and there in the statements of Member States before IOs, but to the author’s knowledge, this is the first time such an exercise has been convened to that explicit end.

The bad news is that only a little over 30 States partook in the exercise. The paucity of participants does not permit the opinio juris expressed to be controlling, or even numerically significant (and this doesn’t seem to be a case where ‘specially interested States’ get to speak for the whole of the community). Moreover, the polarity of the views expressed and the lack of coincidence or majority agreement further subtracts from the critical mass requirement, which is not only a characteristic of the objective element of custom but must be forcibly understood as concurrent for the subjective one. But hey, it’s something!