Customary International Law Symposium: Response from David Stewart

[David Stewart is Professor from Practice; Co-Director, Global Law Scholars Program; Director, Center on Transnational Business and the Law at Georgetown Law.]

As a general proposition, the law prizes clarity, precision and certainty.  Tolerance of ambiguity is not a virtue taught in most law school classrooms.  That’s one reason why beginning students of international law often find it difficult to grasp the notion of customary international law (“CIL”).  It clearly exists.  Just as clearly, it has a foundational place in the international legal structure.   Article 38(b) of the Statute of the International Court of Justice includes (among the law to be applied by that Court) “international custom, as evidence of a general practice accepted as law.”  But how is one to know what qualifies as a general practice accepted as law?

In 2018, after years of deliberation, the International Law Commission answered that question by identifying two constituent elements (“secondary rules,” in Hart’s parlance).  In its formulation, “[t]he indispensable requirement for the identification of a rule of customary international law is that both a general practice and acceptance of such practice as law (opinio juris) be ascertained.”  In other words, “the practice in question must be undertaken with a sense of legal right or obligation.  A general practice that is accepted as law (opinio juris) is to be distinguished from mere usage or habit.”

Prof. Monika Hakimi challenges us to reject the ILC’s “two element” formulation and to change how we think about CIL.  Describing CIL as a set of generally applicable primary rules discernible by the application of such secondary rules, she contends, may reflect what many people imagine it to be but does not reflect what CIL is “as a real-world sociological phenomenon.”  Accurately understood, CIL is more unstable, fragmentary and disorderly than any rulebook would be.  

In the everyday practice of international law, she tells us, CIL “looks nothing like the rulebook conception.” It does not derive from intelligible and generally applicable secondary rules but instead emerges more organically, through an unstructured and “heterarchical” process in which the participants apply variable criteria to justify their normative positions in CIL.  Its content is neither fixed nor generalizable, as rules would be.  

In contrast, Prof. Hakimi invites us to conceive of customary international law as a contingent kind of law, the content of which is “determined not by any secondary rules but by how different normative positions are used and received in concrete settings.”   In the absence of a central authority to determine content, it emerges more enigmatically, through an always-ongoing dynamic, and in consequence its content is more elastic, more variable, than the rulebook conception imagines.  A normative position becomes entrenched enough to operate like a conduct rule only if it actually acquires widespread support.  Its legitimacy derives not from any secondary rules of the sort identified by the ILC, much less any agreed codification, but from the unstructured process through which it is developed and applied.  

Through this “elastic” process, Hakimi contends, global actors can readily use CIL to advance a diverse range of legal claims and thus to catalyze the kinds of interactions that generate new conduct rules, tapping into CIL to defend or challenge a broad range of governance decisions.   This “argumentative dimension” can be especially valuable, she contends, when it does not come at the expense of stable conduct rules.

The idea of law (at least legal principles) derived from actual practice (rather than some central lawmaking authority) begins to make sense to most students when they take into account that even today the international community lacks a central law-making (legislative) authority.  It was only a century so ago that supra-national institutions with some law-making capacity began to emerge on the international level.  Even today, many states remain reluctant to cede sovereignty to external authority, and freely-negotiated treaties (“conventional law”) have long since replaced CIL as the primary source of positive law. 

Most students are disappointed when the answer to their questions about CIL (“what are the rules, where can we find them?”) is “here’s how it evolves.” But describing CIL as essentially an iterative (or constitutive) process of claim and counterclaim is both helpful and correct.  As Hakimi notes, “law does all sorts of things beyond establishing action-guiding prescriptions.”  A focus on the process of authoritative decision-making is of course familiar to anyone trained in the so-called New Haven School of international law, which views international law as a social process aimed at crafting minimum world public order based on the shared values of the international community.

Hakimi is also right to describe such a process as “quintessentially legal in nature so long as it centers on the authority to make particular governance decisions and places this authority outside the hands of any one player.”   Law is more than formal legal rules or institutions and, at least so far, the international community lacks a centralized “law making” mechanism.   Granted, as she also notes, “constituting this kind of argumentative practice is not everything that we want law to do, but it is not nothing. And it happens to be something that CIL does particularly well” – especially given the growing salience of the actions and views of non-state actors on the international level.

What are the implications of this understanding of customary international law?  Beyond enhancing the perceived normative legitimacy of CIL (despite its “messiness”), what difference does it make if we reject the “rulebook conception”?  Hakimi sees particular value in encouraging “global actors” to justify (or contest) particular exercises of power by invoking CIL even when their normative positions are “splintered and contingent.”   We should make it harder, she suggests, for states to disengage from the “argumentative dimension” simply by asserting that CIL does not exist in the absence of rules.  

That makes sense.  As a former “practitioner” of public international law, on behalf of a government, I can agree that it generally seemed more persuasive, more “principled,” even “better,” to ground assertions in terms of legal doctrine than simply to justify them in terms of preferred outcome.   There’s no disagreeing that framing international disputes in legal terms, even when the principles invoked are contingent, contested, even uncertain, can help promote the role and rule of law and preserve “the foundational distinction between sheer power and legitimate authority” (as Hakimi puts it).  

It can even lead to eventual agreement on, and adoption of concrete formulations by the global community (the “settlement of conduct rules” in Hakimi’s terms).  Indeed, she refers to a number of substantive areas in which the “claim and counterclaim” process has over time resulted in the adoption of treaty formulations (such as genocide and the continental shelf) and others in which the process continues (among others, fair and equitable treatment of foreign investors, the use of force against non-state actors, and aspects of foreign state immunity).   Formalizing the agreement in “conventional” terms is certainly not the only way in which the process can be concluded, but it seems to be increasingly preferred.

Are the ILC and Hakimi talking about different things, or at least focusing on different aspects of the same process? 

In rejecting the “rulebook” formulation, Hakimi prioritizes process over product.  Her focus is on the dynamic, contingent, “messy” way in which states and other participants actually engage in the assertion of claims about what should be the agreed principles of customary international law.  Her concern is not simply that the ILC”s “two element” formulation fails to give sufficient credit that process but that it actually devalues or undermines it.   

For its part, the ILC focuses on the product rather than the process – more precisely, the criteria by which the international community can agree that a new rule has gained sufficient recognition and acceptance to be considered as CIL.  Hakimi agrees that a normative position becomes “entrenched enough to operate like a conduct rule only if it actually acquires widespread support.”   The ILC’s formulation can read as simply adding a bit more specificity:  the “indispensable” requirements are “both a general practice and acceptance of such practice as law (opinio juris).” 

Hakimi’s response to this approach is clear: the ILC’s “rulebook” definition necessarily excludes “non-rule-like positions” that are not entrenched but that “routinely have force as CIL.”  Refusing to call them CIL, she contends, is misleading and obscures important parts of the “practice of CIL” by “diminishing the non-rule-like material in CIL that helps to produce settled rules.”

Thinking of law simply as rules, divorced from process, is an impoverished approach.  To contend that process alone is (or can have the force of) law is also unsatisfactory.  Hakimi’s criticism of the ILC approach is that it excludes something in the middle: rules-in-the-making.  Such “emergent rules” (sometimes called “soft law”) should not be excluded, she argues, merely because they are contingent, since they “routinely have force as CIL.” 

It would be too facile to respond that, if such an emergent rule is in fact routinely accepted and given effect as CIL, then it might no longer be considered “emergent” or proto-law.  Nothing in the ILC”s formulation in my view prevents the emergence of new rules of CIL, much less practices that might eventually be accepted as law.  Perhaps what’s needed is an explicit recognition of such an in-between “law-in-the-making” category – including normative principles, supported by a reasonable degree of practice, but not yet sufficiently accepted by the international community and applied in practice to qualify as binding law.  Such an approach might focus attention on, and stimulate helpful discussion of, the issue.  By contrast, it simply confuses the discussion to contend that a particular assertion or practice is the law because it might eventually gain sufficient acceptance to become the law.