Assessing the Authority of the ICRC Customary IHL Study

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If you are desperately in need of some light summer reading, dear readers, I have just the thing for you, inclusive of beach-ready spreadsheets if you want them. Sandy Sivakumaran and I recently posted on SSRN a draft article, ‘Assessing the Authority of the ICRC Customary IHL Study,’ which is forthcoming in the International Review of the Red Cross. The main purpose of the piece is to establish – purely as a descriptive matter, as accurately as possible – the degree of authority currently enjoyed by the ICRC Customary IHL Study in the international legal system, and how that authority has developed over the more than 15 years since its publication. In making this assessment, we focused on patterns of citations to the Study, especially by international and domestic courts.

The essential idea here is that in deciding on which sources to cite, courts are primarily driven by the desire to enhance the persuasiveness and authority of their own decisions, as assessed by their primary audiences. But through citation they also equally reaffirm the authority of the sources they approvingly rely on. Authority is reinforced through habit and repetition, through practice, in an “informal, evolving, and scalar process by which some sources become progressively more and more authoritative as they are increasingly used and accepted.” (Schauer) Thus, the more that international and domestic courts, and other various influential actors in the global legal system, treat an instrument such as the ICRC Study as authoritative, the greater its authority becomes, and the more likely it is for others to start regarding it as authoritative and cite it in their own decisions.

So what have we found? Here’s a hopefully appetizing abstract:

In 2005, the International Committee of the Red Cross (ICRC) published its two-volume Study of customary international humanitarian law (IHL). While upon its publication it was greeted both with acclaim and with criticism, today the Study has become a standard reference work for practitioners and academics alike – indeed, as far as the academia is concerned, it is probably the single most cited work on IHL. But how authoritative has the Study really been in practice? This is the question that we hope to answer in this article.

That question can be framed and approached from many different angles. We have chosen an empirical one, by collecting and analysing citations to the Study in documents containing expressions of State positions, in the judgments of international and domestic courts and tribunals and in the outputs of other influential actors. Our analysis establishes that the Study is increasingly seen as a highly authoritative instrument, such that a particular proposition will be found to reflect customary international law simply on the basis that the Study says so. In the absence of any concerted pushback, particularly by States – and no such pushback appears to be evident today, even if initially that was not the case and there remains some discontent – the Study’s authority will only increase over time, if nothing else then through repetition and force of habit.

The Study’s authority is particularly evident from our survey of the judgments of international courts and tribunals, but the accretion of authority is widespread and not confined to them only. The common tendency to cite the Study as a primary or sole authority for the existence of a customary rule, without any independent analysis and often as if it was a quasi-legislative text, is remarkable. And even relatively trivial but approving citations reinforce the feedback loop of authority. The Study’s authority rests not only on its rigour and the ICRC’s special mandate and expertise, but also on purely pragmatic grounds. The Study fulfils a variety of otherwise unmet needs. Since its publication no rival project was even conceived of, let alone implemented, that could meet those needs. The Study is simply useful, either for genuinely fundamental purposes (such as regulating non-international conflicts) or for purely pedestrian ones (finding cites for non-controversial propositions). And because it will remain useful, and because so many international legal institutions have already treated it as authoritative, the process of accretion is highly likely to continue.

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Mike Schmitt says

July 21, 2022

Anticipate push-back on your findings from many, especially in the United States. Of course, most of those who push back are likely to maintain a copy of the Study in arms reach...and refer to it regularly in their practice.

Gentian Zyberi says

July 22, 2022

Thanks for the "light" reading, Marko. I'll have to take a look. The study, as the name says, is as expected strong in parts and weak in others, despite the Herculean efforts on the part of the team. Most certainly there are a few parts of it which do not pass muster as CIL; some specific issues having been addressed by one State in its reply - including methodological issues. States will not bother much to respond, because most don't have the resources, and because the study is being primarily used in criminal legal proceedings against individuals. Still, would be interesting to hear from you what the assessment of the study would be, if one were to follow the ILC approach in the identification of CIL?

Marko Milanovic says

July 24, 2022

Many thanks for the comments! A couple of points in response:

(1) Mike I don't think that the accuracy of our finding of the Study's increasing authority can seriously be disputed. It's just a fact, looking at the evidence we gathered. States can of course not like this fact.

(2) Gentian actually the Study is not being used mostly in criminal proceedings against individuals. That at least is not our assessment (happy also to provide the spreadsheets). It's being used in all sorts of contexts.

(3) As for my own assessment of the Study, I would just say that the very small number of rules that states have identified as controversial or disputed does not detract from the overall picture, which is that the vast majority of the rules in the Study are customary beyond serious controversy. I genuinely have no firm opinions on the specific rules on which the Study was criticised, and the point of our paper was not really to examine these controversies doctrinally.

Gus Waschefort says

July 25, 2022

Thanks, Marco. A concern I have is the extent to which blind adoption of the Customary IHL Study may have a chilling effect on changing thresholds applicable to norms, as usus and opinion juris develop over time.

Take the prohibition of the use of children in hostilities as an example. Rule 137 provides, "Children must not be allowed to take part in hostilities." The commentary then proposes, rather conservatively, "Although there is not, as yet, a uniform practice regarding the minimum age for participation in hostilities, there is agreement that it should not be below 15 years of age."

There is a very strong argument that for use in hostilities, as opposed to recruitment, the age threshold established jointly by usus and opinion juris, is younger than eighteen. Nevertheless, it certainly is younger than 16 and not younger than 15.

The more the CIL age threshold is routinely restated as younger than 15, inter alia by reliance on the Customary IHL Study, the more it inhibits the customary development of the norm. In a way this concern is on the opposite end of the spectrum to state pushback against the norms defined in the study. Gus.