International Law: System or Set?

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“International law is a system …. not a random collection of [] norms.” So concluded the International Law Commission’s Study Group on the Fragmentation of International Law in 2006. Legal philosophers immediately recognized the target. In a footnote to their full report, the Study Group named him:

The view that holds international law a “primitive” structure bases itself on the claim that the rules of international law do not form a “system” but merely an aggregate of (primary) rules that States have contracted. See H.L.A Hart, The Concept of Law (Oxford: Clarendon Press, 1961) pp. 208-231.

Why did Hart say that the rules of international law “constitute not a system but a set of rules” (CL 236)? Was he right? In his wonderful book, Philosophy and International Law: A Critical Introduction (PhIL), David Lefkowitz offers a new reading of Hart that is simple and powerful. If David is right about Hart, and Hart is right about international law, then international law is not a system and likely never will be. But something is missing from David’s reading. Or, rather, someone.

Rules and Rulers

As David explains, Hart spends most of his famous Chapter X refuting various forms of international legal skepticism. International law is law, not ‘positive morality’ as Austin claimed. It binds sovereign States and is reasonably effective despite mostly decentralized and non-coercive enforcement. International law and municipal law are sufficiently analogous in function and content to fall under the same concept, but sufficiently disanalogous in form that “the sceptic’s last doubts about the legal ‘quality’ of international law” cannot yet “be laid to rest” (CL 237).

What did Hart mean by ‘form’? Did Hart simply mean that “the formal structure of international law lack[s] a legislature, courts with compulsory jurisdiction and officially organized sanctions” (CL 232)? Or did Hart mean that international law resembles, “in form though not at all in content, a simple regime of primary or customary law” that lacks secondary rules of recognition, change, and adjudication (CL 232)?

As David reads him, “Hart does not deny the presence of secondary rules in international law” (PhIL 33). Hart merely observes that international law’s secondary rules do not establish institutions that recognize, change, and adjudicate primary rules on behalf of the entire community. The law of treaties empowers States to deliberately change their own legal rights and obligations. But no international legislature can deliberately change the legal rights and obligations of all States. International law is full of courts, but none empowered to apply all of international law to all its subjects. On David’s reading, “it is actually the contrast between a society that lacks specialization in the performance of governance tasks and one that possesses such specialization that informs Hart’s reflections on international law” (PhIL 32).

What of Hart’s claim that international law lacks “a unifying rule of recognition specifying ‘sources’ of law and providing general criteria for the identification of its rules” (CL 214, cf. 236)? David suggests that the absence of an international rule of recognition follows from the absence of an international legislature. International law lacks a hierarchy of rules because it lacks a hierarchy of rulers and ruled (PhIL 35-38). If primary rules are not intentionally created by officials and institutions, then they can only arise unintentionally from custom. Custom exists as a matter of social fact, and any attempt to formulate criteria establishing custom’s legal validity will produce only a “useless reduplication of the fact that a set of rules are accepted by states as binding rules” (CL  236).

David’s reading of Hart is plausible but pessimistic. No one expects an international legislature or international courts of general and compulsory jurisdiction anytime soon. But I don’t think David’s reading is entirely correct.

Hart thought and wrote in response to someone else, and only by understanding him can we understand Hart. David’s book never mentions him, but Hart’s book mentions him more than anyone besides John Austin. He was “the only theorist who appear[ed] to preoccupy” Hart as he wrote. Hart later named him as one of the foreign legal thinkers who most influenced his intellectual development. He was also the greatest philosopher of international law of all time.

Hart versus Kelsen

According to Hans Kelsen,

International law is still a primitive legal system …. It is still marked by wide-ranging decentralization—at least in the field of general international law, and thus as it affects the entire international community. There are still no organs, whose respective functions reflect a division of labour, for creating and applying legal norms.

Hart agreed, as David shows. Kelsen thought general international law consists of the various customary rules arising from State behavior, including the customary rules regarding treaties. Particular international law mostly consists of rules created by treaties, including the rules constituting international courts and organizations. These courts and organizations may apply or issue rules to consenting parties. Hart agreed, stating that the rules of treaty-formation are just rules of customary international law, and international organizations are just treaty bodies.

Nevertheless, Kelsen thought international law was united into a hierarchically organized legal order by a basic norm “that establishes custom … as a law-creating material fact.” Hart did not agree. Hart felt no need to presuppose

the strange basic norm which has been suggested for international law: ‘States should behave as they have customarily behaved’. For it says nothing more than that those who accept certain rules must also observe a rule that the rules ought to be observed. This is a mere useless reduplication of the fact that a set of rules are accepted by states as binding rules.

Hart was wrong. Kelsen’s basic norm was not a social rule reducible to social facts about how States behave or what States accept or observe. Normative statements are not ‘reduplications’ of descriptive statements. But that’s not the point. The point, for now, is that without a basic norm to unite them into a single legal order, the various rules of customary international law form not a system but a mere set.

Hart’s disagreement with Kelsen did not turn on the presence or absence of legal institutions. They had the same disagreement regarding municipal law, which is full of legal institutions. As Hart wrote,

If a constitution specifying the various sources of law is a living reality in the sense that the courts and officials of the system actually identify the law in accordance with the criteria it provides, then the constitution is accepted and actually exists. It seems a needless reduplication to suggest that there is a further rule to the effect that the constitution (or those who ‘laid it down’) are to be obeyed. (CL __)

Hart thought municipal legal systems are united by a social rule—an ‘ultimate’ rule of recognition. International law has many social rules—the rules of customary international law—but no ultimate social rule that unites them all into a system. Hart’s fundamental objection to Kelsen was that nothing above, below, or behind social rules is either necessary or sufficient to unite a legal system.

This reading explains why Hart devotes only three paragraphs of his final section to the institutional disanalogies between international and municipal law but devotes four pages to the “suggested formal analogy” that, “like municipal law, international law possesses and indeed must possess a ‘basic norm’ … in virtue of which the rules constitute a single system” (233). Hart did not think the absence of institutions entailed the absence of a basic norm. Hart thought Kelsen’s basic norm did not exist as a matter of social fact and need not be presupposed as a matter of legal theory.

This reading also makes some sense of the puzzling passage in which Hart writes that 

it is sometimes argued that [multilateral treaties] may bind states that are not parties. If this were generally recognized, such treaties would in fact be legislative enactments and international law would have distinct criteria of validity for its rules. (CL 236)

David says that, in this scenario, international law would “include the distinct categories of rulers (or officials) and ruled (or subjects), and so no longer be aptly characterized as a horizontal political order” (PhIL 34). This is very hard to see. Suppose States accept that any treaty ratified by two-thirds of them binds them all. International law would have general legislation but no standing legislature, a secondary rule of change for general international law but no distinct categories of rulers and ruled. Hart thought such a secondary rule could be understood, not as an ordinary rule of customary international law, but as a hierarchically superior rule of an international legal system.

(Who “sometimes argued” that treaties may bind non-parties? Kelsen. But that’s another story.)

Finally, in his 1968 essay, “Kelsen’s Doctrine of the Unity of Law,” Hart wrote that a rule’s membership in the municipal legal system of a State depends on the recognitional practices of that State’s courts.

But we cannot leave out of sight more primitive arrangements: there may be no courts and no specialized enforcement agencies, and the application of sanctions for breach of the rules may be left to injured parties or their relatives, or to the community at large. International law, at least according to Kelsen, is itself such a decentralized system. Presumably, in such cases we shall have to use as our test of membership the notion of recognition by the society or the community, and certain problems in defining what constitutes sufficient recognition will have to be faced. (EJP 340)

The community of States could recognize all rules that satisfy some general criterion as members of the decentralized system of international law. But, Hart thought, they didn’t, and for that reason—not the absence of centralized institutions—international law remained a set, not a system, of rules.


The ILC Study Group took a different doctrinal stance, with different theoretical implications. Treaty is a source of law, distinct from custom and equal in rank. So are general principles of law, which Kelsen questioned and Hart ignored. The different sources are not ranked in any general order of priority, but potential conflicts are avoidable or resolvable through contextual application of general considerations. And peremptory norms (jus cogens) are hierarchically superior to all others. From this more complex arrangement, one might formulate an ultimate social rule of recognition and supreme criterion of legal validity that unites international law into a system without the centralized institutions that David’s reading of Hart demands.

David’s book mentions peremptory norms only in passing, but their significance cannot be overrated. According to the ILC, a rule of customary international law does not come into existence if it conflicts with an existing peremptory norm, and ceases to exist if it conflicts with a new peremptory norm. It follows that rules of customary international law do not simply exist as a matter of social fact. Instead, custom is a law-creating material fact only to the extent that higher norms permit. Hart wrote before peremptory norms took center stage. But they were first invoked in the Security Council a decade earlier, with much at stake, on the authority of a single scholar. David’s wonderful book never mentions him. But he was the greatest philosopher of international law of all time.

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Miodrag Jovanovic says

November 8, 2021

Anyone watching Victor Burgin’s well-known photograph from the series US77 assumes the viewpoint of the front-seat passenger of the moving vehicle ahead of which is a seemingly unfolded straight, flat, and empty road. Despite this view, the photograph is somewhat puzzlingly entitled False Perspective. The author seems to suggest us that no matter how simple is the landscape of physical reality, in order for its particles to be soundly linked into a single scene, a viewer has in some way to connect them, thereby necessarily becoming involved in the process of personal construction. The outcome of this process is a viewer’s “perspective.” However, in what sense, then, can something that is the result of an individual construction ever be said to be “false,” or “truthful” for that matter? The only plausible response would be to translate the demand of “correctness” of a perspective into the request for “coherence” in one’s attempt to make aforementioned connections, with the purpose of organizing one’s own experience.
I am using this metaphor in my recent book The Nature of International Law (Cambridge University Press, 2019) in order to show that, unlike the landscape from Burgin’s photograph, legal reality is far more complex and that, in trying to make connections between different particles of specific raw data, a legal philosopher has to engage partly in the business of “stipulative regimentation” (Raz) of the empirical knowledge, thereby necessarily imposing on it his/her own theoretical construction of that reality. On this account, “correctness” of a theory of (international) law has to be translated into the request for its “coherence” in light of some predefined theoretical purposes. Hart obviously engages in such business when proposing to treat law “as the union of primary and secondary rules” under the broader perspective of “systematicity.” And, then, he discharges Kelsen’s perspective of international law as a legal system as “false”, insofar as “international law simply consists of a set of separate primary rules of obligation which are not united in this manner.” (The Concept of Law, 233)
Now, Lefkowitz argues in his new book that, although Hart has given enough incentives for this line of criticism, it is not for the reason of the lack of hierarchy of rules, but hierarchy of rulers, that he was suspicious about full-fledged ‘legality’ of international law. (Philosophy and International Law, 32) Ahmad Haque persuasively shows that even if this reading of Hart, to which Lefkowitz subscribes, is plausible, it is, nonetheless, problematic. I want to add two more reasons: 1. If, for Hart, law’s obtaining the “systemic” feature serves the goal of remedying the ills of uncertainty, static character of the rules, and inefficiency, then it is justifiable to employ the functionalist approach in determining whether international law pass the threshold of “systematicity” – on the functionalist account, it would be difficult to claim that international law is not a legal system; 2. in its Fragmentation report, the ILC at one point says that “systemic thinking penetrates all legal reasoning, including the practice of law-application by judges and administrators” (par. 35), i.e. lawyers represent their specific reality as if (als ob) it is coherent, integrated, and unified whole – I argue in my book that that there are credible signs that international adjudicative bodies, even those of special international legal regimes, do depict themselves as officials of international legal order and treat international legal rules as if they are belonging to a unified legal system.