Obligation

Since at least Plato's Socratic dialogue Crito, Philosophy and Political Theory have been concerned with the questions of why and when obedience is due to the government and its laws. Since the Reformation, questions of dissent and resistance, and the relationship between authority and obligation have become central to discussion of political obligation. Questions of when and why obedience is due link Political and Legal Theory; the latter particularly has concerned itself with the explaining the bindingness of rules (a distinct matter from explaining compliance with them; Koh Reference Koh1997; Kingsbury Reference Kingsbury1998; Guzman Reference Guzman2002; Raustiala and Slaughter Reference Raustiala and Slaughter.2002).

As indicated in the Introduction, the particular modes of obligation with which this essay is concerned are obligations that are peremptory or categorical in character. Political Theory has had very little to say on these particular matters, largely relegating them to Moral Philosophy. The latter has long tended to speak in absolutes and universals. Kant (Reference Kant1785), of course, famously traded on both of these dimensions in the various formulations of the Categorical Imperative (Kant 4:402-403; 4:420-21 (The Formula of Universal Law); 4:427-29 (The Formula of the End in Itself); 4:433-36 (The Formula of the Kingdom of Ends)).

Positivist understandings of the law, by contrast, have long eschewed discussion of the moral character of rules, but one proffered way to understand jus cogens and to understand the place of jus cogens in the law is as re-asserting a moral standard to which voluntarily derived agreements must comply if they are to bear the character of law. (There is a debate within positivism over the exact character of the relationship between morality and legality that will be addressed below, but for now, what should be noted is that the form of positivism that we find in International Law has generally followed a strict separation of law and ethics.) As we will see below, this is a signal rejection of one of the key tenets of the form of positivism dominant in International Law, but one that has come from within.

Obligation per se has not been a dominant theme in the Ethics and International Relations literature. A key place where this literature addresses abstract issues of obligation is in the Cosmopolitan–Communitarian debate (Brown Reference Brown1992; Jones Reference Jones1999; O'Neill Reference O'Neill2000; O'Neill Reference O'Neill2001; Hayden Reference Hayden2005; Caney Reference Caney2010). Although this debate has mostly played out over the question of the extent of moral community, what is wrapped up in this issue is the question of the extent of moral obligation. In the very simplest of terms, the Cosmopolitan position is that moral community is universal, and our moral obligations to one another are likewise universal in both scope and extent; conversely, Communitarians hold that moral community and the moral obligations that come from membership in a particular community are tightly circumscribed (Cochran Reference Cochran1999; Cochran Reference Cochran2001; Rorty Reference Rorty2001). The nature of obligation generally is not under discussion in the Cosmopolitan–Communitarian debate however, and the idea of categorical obligation only appears in the context of its association with Kant who is often, if not uncontroversially, considered a cosmopolitan (Nussbaum Reference Nussbaum1995; Gould Reference Gould1999, 32–34).

The positivist–voluntarist understanding of obligation that was introduced previously offers a very specific understanding of obligation (and is, of course, concerned narrowly with legal obligation), but this is only one possible way of conceptualizing obligation. Hobbes – whom we might read as a progenitor of this tradition – divided obligations into two sorts, obligations in foro interno and obligations in foro externo. Obligations in foro interno, with which he associated natural law, were not externally binding, and were therefore not humanly enforceable, while the opposite held for obligations in foro externo (Flathman Reference Flathman1993, 56–57; May Reference May2005, 17–18; Hoekstra Reference Hoekstra2007, 120–21).

The natural law tradition made a four-fold distinction between necessary and voluntary obligations on the one hand, and between perfect and imperfect obligations on the other. The former pairing differentiated along the axis of the compulsory or non-compulsory character of the obligation. Perfect obligations – the corollary of perfect rights – could have their performance demanded or compelled. Imperfect obligations, conversely, could not have their performance compelled; they ‘give but the right to request’. Imperfect obligations – at least in the law – could be transformed into perfect obligations by being put into a formal agreement, that is, a contract or a treaty.

Kant's aforementioned discussion of ethics in The Groundwork, which set the stage for his discussion of law in The Doctrine of Right (Part 1 of The Metaphysics of Morals), differentiated between categorical obligations and hypothetical obligations (he maintained as well the perfect/imperfect obligation distinction in The Doctrine of Virtue, Part 2 of The Metaphysics of Morals, both with regard to obligations to others and to obligations to oneself). Categorical obligations, as we shall see below, demand unconditional compliance; they are absolute and exceptionless. Hypothetical obligations, by contrast, are binding only insofar as one possesses a particular end (Kant 4:441).

As a case study in problems relating to conceptualizing obligation at the international level, this essay will examine how and why notions of categorical obligation (analogous to the natural law tradition's ‘necessary obligations’) have been brought into the seemingly intellectually inhospitable environment of positivism, and how positivists have done so only by radically denaturing this mode of obligation. In the next section, we will look more closely at positivism and voluntarism to get a better sense of why it is that jus cogens would seem such an odd fit in a system characterized by these modes of conceptualizing legal obligation.

Positivism and voluntarism

Both ‘positivism’ and ‘voluntarism’ are particularly vexed terms; because they will figure prominently throughout, some further clarification is in order. There are, of course, numerous positivisms. A family resemblance term in Wittgenstein's sense, all of these uses share an ontological commitment to studying clearly parse-able objects of the world, and hence bear a debt to the Cartesian Mind–World separation. We find the term used in Philosophy of Science and Philosophy of the Social Sciences with a meaning originally set out by August Comte, and sharing a complicated relationship with Empiricism and Scientific Realism. It is found as well in Logic in the traditions associated with both Bertrand Russell and the Vienna Circle. Its manifestation in Ethics went by the name ‘Emotivism’, and was associated inter alia with C.L. Stevenson and A.J. Ayer.

As it will be used here, ‘positivism’ refers to its usage in legal theory; in this context, it denotes laws that have been set out – posited – by human lawmakers, rather than being intrinsic to the natural order (natural law) or ordained by god (divine law). ‘…it is put or set by its individual or collective author, or it exists by the position or institution of its individual or collective author’ (Austin Reference Austin1832, Lecture V). Having been posited, there will always be some form of evidence of the law and its content. ‘…its essential meaning in… international law is reliance on the practice of states and the conduct of international relations as evidenced by customs or treaties, as against the derivation of norms from basic metaphysical principles’ (Damrosch et al. Reference Damrosch, Henkin, Murphy and Smit2009, xxii).

H.L.A. Hart, a prominent 20th century legal positivist, noted five uses of the term ‘positivism’ in the law:

1. (1) the contention that laws are commands of human beings,

2. (2) the contention that there is no necessary connection between law and morals or law as it is and ought to be,

3. (3) the contention that the analysis (or study of the meaning) of legal concepts is (a) worth pursuing and (b) to be distinguished from historical inquiries into the causes or origins of laws, from sociological inquiries into the relation of law and other social phenomena, and from the criticism or appraisal of law whether in terms of morals, social aims, ‘functions’, or otherwise,

4. (4) the contention that a legal system is a ‘closed logical system’ in which correct legal decisions can be deduced by logical means from predetermined legal rules without reference to social aims, policies, moral standards, and

5. (5) the contention that moral judgments cannot be established or defended, as statements of facts can, by rational argument, evidence, or proof (‘noncognitivism’ in ethics)… (Hart Reference Hart1958, 601–602).

As noted by Hart, positivism tends toward a separation of law and ethics – again in distinction to naturalism; it professes to offer a ‘morally neutral descriptive or conceptual theory of law’ (Bix Reference Bix2004, 120). It professes to be concerned with law as it is rather than law as it should be; in Austin's earlier rendering, ‘The existence of law is one thing; its merit or demerit is another’ (Austin Reference Austin1832; Bix Reference Bix2004, 120). Positivism regards laws as normative, but takes no normative stance on the moral quality of laws, effectively and at times expressly separating law from justice, which has the effect of ‘conferring upon positivism a certain moral ambivalence’ (Neff Reference Neff2006, 40).

As noted earlier, however, this is no longer a uniform position within positivism. Since at least the publication of the postscript to Hart's The Concept of Law, the question of the relation of law and morality has been re-opened (Hart Reference Hart1961). We now find two camps within positivism: those who follow the stricter Austinian line (or modern versions of it) are called Exclusive Positivists, while those who follow Hart's lead and allow for at least the possibility of a place for moral consideration in the evaluation of laws are called Inclusive Positivists. Rather than the rigid barrier of the Exclusivists who assert that ‘the definition of law must be entirely free of moral notions’, Inclusive Positivists, while denying that ‘the legality of a norm necessarily depends upon its substantive moral merits…’ note that ‘there are conceptually possible legal systems in which the validity criteria include substantive moral norms’ (Himma Reference Himma2002). Inclusivists thus allow for the inclusion of extra-legal moral criteria in the evaluation of a law, but simply deny that satisfying moral criteria is necessary for a rule-candidate to qualify as a law. They do not reject the possibility of there being moral criteria to establish legality, but assert that it is possible for there to be a legal system that does not have moral criteria for evaluating laws. Likewise, they hold that it is possible for there to be a legal system that does include moral criteria (Bix Reference Bix2005, 37–38). The Inclusivist position is best characterized as agnostic about moral requirements, while the Exclusivists actively deny, ‘a legal system can incorporate moral constraints on legal validity’ (Himma Reference Himma2001). The Inclusive form of positivism, however, has not caught on in international law, and it is not reflected in state practice or in the jurisprudence of international tribunals. If it were, the incorporation of categorical obligation would present no explanatory difficulties, but Exclusivism still dominates within International Law; for this reason, all further references to positivism shall be to Exclusive Positivism.

Without explicit reference to the source, positivism accepts and builds upon Hume's distinction between (and rigid separation of) ‘is’ and ‘ought,’ and indeed upon deeper Hobbesian roots (Hobbes Reference Hobbes1651, II.XXVI.5–6; Hume Reference Hume1739, III.I.I). What distinguishes a law for positivists is not its agreeability to any given moral framework, but rather its ‘pedigree’ to use Austin's terminology – the authority to promulgate laws of those who posited a given law. The ‘Pedigree Thesis’ or ‘Sources Thesis’ placed explanatory emphasis for the obligatoriness of a law candidate on its source; ‘the existence and content of law can always be determined by reference to its sources…’ (Morgenthau Reference Morgenthau1940, 265; Himma Reference Himma2002, 140). Indeed, what is called ‘Sources Doctrine’ in International Law is a direct outgrowth of the ‘Pedigree Thesis’. By delineating an exclusive set of authoritative sources such as are found in Article 38(1) of the Statute of the International Court of Justice, or Sections 102 and 103 of the Restatement 3 ^rdof the Foreign Relations Laws of the United States (American Law Institute 1987), positivist international law simply recapitulated the Pedigree Thesis.

It bears repetition that the positivism one finds in International Law is not the nuanced form that has arisen in the wake of Hart's critiques of Austinian positivism; International Law is still dominated by what is essentially a 19th century understanding of positivism in which there is a barrier between law and ethics, in which it is still understood that sovereigns bind themselves, and can only be bound by their own consent. Indeed, International Law ‘has gone back at least to the point from which positivism started in the last decades of the nineteenth century’ (Morgenthau Reference Morgenthau1940, 264).

Voluntarism holds that legal obligation over an agent can only be created by the consent of that agent, that is, for a state to be legally bound it must have consented (willed) to be bound. ‘A strictly voluntarist view of international law rejects the notion that a State may be bound to an international legal rule without its consent… In international law there are no rules other than such rules as may be accepted by the state concerned’ (Koskenniemi Reference Koskenniemi2005, 233; Shelton Reference Shelton2006, 164–65). Obligation comes only from consent-to-be-bound in this understanding.

This necessarily entails the specificity of obligation. Unlike natural law, which was either definitionally or stipulatively universal, the requirement of specific consent made all obligations specific solely to contracting parties. At the international level, we might equate this understanding of voluntarism with sovereignty in its more absolute forms. Indeed many 19th century articulations of the concept of sovereignty (perhaps Hegel's most pointedly) framed it in just such terms. In the 19th century, ‘…the voluntary law, freely fixed upon by the States themselves, came to be regarded as the only true source of law. As the World Court would later put it, “…the rules of law binding upon States… emanate from their own free will” ’ (Neff Reference Neff2006, 39). It was a commonplace throughout that period that to be sovereign meant to be autonomous; to be sovereign was to be subject to (bound by) no obligation to which the state had not voluntarily subjected itself and from which it could not free itself at will. If some other party had the power to impose laws upon the state then that ‘state’ was definitionally not sovereign, because to be sovereign was to be subject to no higher authority; to be sovereign was to be autonomous – to be sovereign was to be the sole author of your obligations. For a time, sovereignty was itself thought of as if it was a categorical rule – or perhaps more appropriate a categorically binding assemblage of rules.

As these doctrines developed in international law, they have come to signify the position that states are bound only by such rules as they have (voluntarily) created and have consented to have to bind them. This is perhaps one of the most fundamental understandings of modern International Law. To repeat Henkin's assessment from above, ‘State consent is the foundation of international law. The principle that law is binding on a state only by its consent remains an axiom of the political system, an implication of state autonomy’ (Henkin Reference Henkin1995, 27). It has been repeatedly asserted by states and consistently upheld by international tribunals, especially the Permanent Court of Justice (PCIJ) and the International Court of Justice (ICJ), where it has formed one of the bedrock rules of jurisdiction and admissibility (Damrosch et al. Reference Damrosch, Henkin, Murphy and Smit2009, 57–58, 76). Positivism and voluntarism rejected the very idea of obligations that states could not shed. They likewise rejected any suggestion of indefeasible obligations. As products of the (reified) wills of (reified) states, international law was understood to bind states only insofar and only so long as they willed (consented) to be bound; international law bound states only at their pleasure in this understanding. Allain Pellet outlines the logic as follows:

• • law = jus positum, that is rules which are formed through certain formal channels; this is the ‘positivist’ approach;

• • jus positum = jus voluntarium, that is the rules which are based on the will of states, and only those rules; this is the ‘voluntarist’ approach (Pellet Reference Pellet1988–89, 23).

Slowly throughout the 20th century, the dominance of the absolute quality of this doctrine – in conjunction with any suggestion of the absolute quality of sovereignty – has been progressively challenged, and notions of categorical obligation, as well as universal forms of obligation have re-emerged, but these challenges have arisen within what still remains a largely voluntarist framework. As sovereignty has become attenuated, the idea that there are some sorts of obligations that might trump sovereignty has re-emerged (Brown Reference Brown2002). We will return to this issue in the section ‘Categoricals in a voluntarist setting’.

While I have asserted throughout this section that positivism and voluntarism constitute the dominant explanation of obligation in law, that is by no means to suggest that this explanation is without serious conceptual problems; in particular, the idea that consent/will is the source of all legal obligation faces a number of serious problems. The most pressing problem with basing obligation in consent, and the most common challenge to voluntarism, is the question of what makes consent-to-be-bound generate obligation. It is an issue of regress: in order for consent to generate obligation, there must be a prior norm establishing the rule that consent generates obligation, and that prior norm cannot be rooted in consent, or else there must be a yet antecedent rule making that act of consent generative of the obligation, and so on ad infinitum. For these reasons, Roberto Ago famously asserted that basing obligation in consent is a ‘myth’ (Ago Reference Ago1957, 699).

The regress issue was recognized by positivists; one of their proffered solutions was the ‘grundnorm’ of Hans Kelsen's Pure Theory, a stipulative bedrock, the origin of which was put outside the realm of legal analysis, and made a matter of sociological inquiry (Kelsen Reference Kelsen1967, 193–221). Another answer was suggested by Hart, within his schema of primary and secondary rules (Hart Reference Hart1961, 79–123). This aporia is also a common starting point for modern natural law theorists to begin their critiques of positivism (Dubois Reference Dubois2009, 134, 142–48). As a way to obviate the regress problem, they postulate or deduce a series of fundamental norms with which all positive law must accord.

While these critiques of the underlying logic of positivist voluntarism are indeed compelling, it remains the case that state practice and international judicial practice are still dominated by positivism and voluntarism. International Law still proceeds as if consent was not only an unproblematic basis for the creation of obligation, but the sine qua non of obligation. Jus cogens and the categorical – and by some accounts non-voluntary – obligation it entails are represented by many as a fundamental challenge to this orthodoxy, and by some as further evidence of the orthodoxy's incoherence, but as I will show in what follows, rather than succumbing to any challenge presented by jus cogens, the orthodoxy has, in fact, domesticated jus cogens, keeping the conceptual vocabulary, but abandoning the logically attendant practices, especially where they directly confront sovereign prerogatives. For example, in the ICJ's decision in the Arrest Warrant case, universal jurisdiction over international criminals was trumped by sovereign prerogative. Although domestic jurisprudence (i.e. Pinochet III) has shown that the violation of jus cogens norms is not protected by sovereign (head of state) immunity, the ICJ has not followed this path. Likewise, violations of jus cogens norms have been held to be non-actionable in the absence of the consent of the accused state (East Timor). In both Arrest Warrant and East Timor, traditional sovereign voluntarism dominated the Court's reasoning, and the issue of the jus cogens character of the obligations violated was not addressed (Shelton Reference Shelton2006, 167; Gould Reference Gould2010, 68–74, 100–104).

It is important to recognize that in the period of positivism's dominance, the very idea of a ‘hierarchy of norms’, the idea that some norms are ‘more binding’ or ‘more imperative’ than others, or to use Prosper Weil's phrase, the idea of ‘relative normativity’ was treated as if it were conceptually incoherent (Weil Reference Weil1983). The ideas that some norms could not be contracted out of, that some norms could never be legitimately violated were similarly treated as incoherent if not anathema. As problematic as basing obligation on consent is, the dominant understanding was that the only limits on states’ unfettered freedom of action were understood to be those voluntarily undertaken by states, and those undertakings were understood to always be subject to subsequent renunciation when the willingness to be bound ceased. The hegemonic view is deeply flawed, but remains hegemonic nonetheless.

In the next section, we turn to semantic and lexical questions about the labeling of these types of obligations and the unseen consequences of labeling; this will offer some explanatory purchase when we turn to the question in the subsequent section of such obligations’ fit within modern positivist international law.

Deadly rules

Some terminological clarification is in order. Neither etymology, semantics nor conceptual history determines usage at any particular point in time, but they always at least color it, and the very semantics of ‘jus cogens’ betray a bit of confusion. In essence, there is a mismatch between the meaning of the term and its meaning-in-use; while we might follow Wittgenstein, and obliterate that distinction, this would not help to clarify the conceptual confusions that have resulted from the semantic and lexical issues. The value of this discussion of the semantics of the language associated with jus cogens will become apparent below when we explore the doctrinal debates associated with this sort of norm.

Lakes of ink have been spilled over the ‘essence’ of peremptory norms in an effort to try to come to grips with the practical import of a few short sentences in two articles of the Vienna Convention. Much of the exegetical furor can be attributed to divergences in the underlying understandings of what the words mean apart from their narrow use as legal terms of art. Commentators have not been able to arrive at mutually agreeable answers because their very language cannot accommodate matters; in Wittgenstein's terms, we are confronted with two different language games: the voluntarist language game associated with positivism, which understands all obligations as voluntary, derogable, and ultimately transient, and the naturalist language game of categorical obligation, which regards a particular sub-set of obligations as necessary, timeless, and indefeasible (Wittgenstein Reference Wittgenstein1953, para 7).

The literature, and of course, the Vienna Convention use the term ‘peremptory norm’ for jus cogens; indeed, the Latin appears only parenthetically in a heading title in the Vienna Convention. The word ‘imperative’ is also widely used – ‘imperatif’ is used rather than ‘peremptory’ in the French text of the Vienna Convention. We need to very closely parse the semantic distinctions between these terms and my preferred term, ‘categorical’ to fully clarify why this is such a problematic fit within the positivist tradition. Basically, because the denotations of these terms do not adequately capture the absolute quality of this class of obligations, they conceal how conceptually and practically awkward the fit is between jus cogens and positivist international law.

‘Peremptory’ in its legal usage can be traced back at least as far as Gaius’ Institutes; in the discussion of exceptions to actions, a distinction is drawn between ‘peremptory’ and ‘dilatory’ exceptions, in which the former ‘cannot be evaded’ (Gaius IV.120-21). Outside of its legal context, the literal meaning of ‘peremptorius’ was ‘deadly’ or ‘destructive’, from this base it was adapted for the law to connote ‘decisive’, ‘precluding all debate’, or ‘putting and end to’ (a fine euphemism for killing). One cannot help but be somewhat troubled, however, by the idea of deadly or destructive norms. In modern usage, ‘decisive’ and ‘admitting no refusal’ are the dominant aspects of the term's meaning. If a rule is peremptory, compliance with it cannot be refused; if there is a rule in conflict with a peremptory norm, it rather than the conflicting rule is decisive. To stretch the metaphor a bit, it kills the other rule. This gets us part of the way to explaining the character of jus cogens obligations, but it does not convey the full sense of norms that operate ‘in an absolute and unconditional way’.

If death is at the root of ‘peremptory’, violence is at the root of ‘cogens’. ‘Cogo’ (of which cogens is the present participle) literally meant to ‘force’, to ‘drive together’, ‘compel’, or ‘constrain’. The English ‘cogent’, which derives from ‘cogo’, still connotes power or force, even if in ordinary language only in the sense of the power or force of a proposition or argument. ‘Constraining’ and ‘compelling’ are still part of things, but none of the aspects of the pragmatics of cogens really convey much of what distinguishes jus cogens from jus dispositivum (laws that are ‘subject to the dispensation of parties’; in this case, laws that fall squarely within the traditional voluntarist understanding of obligation). All rules are constraining or compelling. Some rules are considered more compelling than others, and some do not permit exception, but there is nothing in the meaning of the term that immediately links jus cogens with its meaning-in-use.

Having moved from death to violence, turning to ‘imperative’, we come to command (leaving neither death nor violence far behind, however). Imperative shares a root with ‘empire’. ‘Impero’ is to ‘command’ or ‘rule over’; its cognate, ‘imperium’, had both a military and a legal–political sense, but

In its legal–political sense, higher magistrates of the Republic were granted imperium (its military roots still in evidence by the magistrate's accompaniment by fasces-wielding lictors), but it was of a narrower, more restricted sort than that possessed by military commanders. It was, nonetheless coupled by coercitio, the right of coercion and punishment, making violence a near definitional conjunct of imperium.

In its modern usage, ‘imperative’ is still closely tied to command; it is no longer associated with office or role, but now characterizes language. The imperative grammatical mood is linked semantically to directive speech acts (‘do x’), which are associated with hierarchy as a form of rule (Onuf Reference Onuf1989; Onuf Reference Onuf1998). ‘Imperative’, like ‘cogent’, would seem to be redundant as a descriptor of a rule. All rules ‘demand obedience’; while all rules might not be formulated as commands, most laws are: most laws either command an action or forbid an action (which is to do no more than command that an action not be taken).Footnote 2 To say that a law or norm is imperative is to do nothing more than circularly indicate that it has law-like qualities.

As we saw in the introduction, ‘categorical’ is a term more often associated with ethics than law, although one does find the term used in liability and in regulatory law. It is Kant's usage of ‘categorical’ that comes closest to what jus cogens means in international law: a category of obligation that is ‘absolute’ and ‘unconditional’ (Kant 4:416). Neither ‘peremptory’ nor ‘cogent’ nor ‘imperative’ carries the same sense of the absolute and unconditional as ‘categorical’; it alone among these terms entails being exceptionless (Orakhelashvili Reference Orakhelashvili2006, 67). Combining this with ‘peremptory's’ sense of ‘decisive’ gives the full sense of jus cogens’ use in international law. We see that jus cogens norms are thought of as categorical obligations most clearly in judicial practice. Cases, both domestic and international, in which jus cogens have been invoked, have expressly treated such obligations as absolute and unconditional.

This combination of unconditionality and decisiveness makes clear the awkwardness of trying to make jus cogens fit within an understanding of international law still dominated by the tenets of positivism and voluntarism. Within these systems, obligation is normally never unconditional; to revert to the language of Kant, for positivist–voluntarists, legal obligation is always hypothetical. Yet in the case of jus cogens, we have positivist international law trading in unconditional obligations, and introducing them through that most positivist of means, the multilateral treaty. In the next section, we will trace the history of the idea of categorical legal obligation to shed some light on the issue of why positivism has incorporated the idea and language of categorical obligation into its normative complex.

The conceptual history of categorical legal obligation

We might clarify how and indeed why the language of categorical obligation has been brought into otherwise voluntarist international law by looking to its evolution in the law more generally. Although the idea of categorically binding laws was contained in Roman Law, the term jus cogens appears only once in Justinian's Digest, in a passage from Papinian, ‘Donari videtur quod nullo jure cogente conceditur’.Footnote 3 The concept was subsumed under the heading of the jus publicum, and is summed up in the rule ‘Jus publicum privatorum pactis mutari non potest’, which Gaius claimed could be traced back to the Laws of Solon.Footnote 4 What is important about this rule is that it stipulates the existence of a class of obligations that is normatively superior to all others, and that does so without reference to any extra-legal mechanisms. It is problematic to directly link Roman law to modern positivism, but in this instance, there is a meaningful parallel.

The idea of a class of obligations normatively superior to all others could be found later in the classical International Law literature under the label the ‘Necessary Law of Nations’; as part of natural law, the ‘Necessary Law of Nations’ was understood to have ‘existed outside the will of states’ (Paul Reference Paul1971, 20; Parker and Neylon Reference Parker and Neylon.1989, 419–22). The concept paradoxically found its apotheotic expression in Christian Wolff and Emer Vattel, the very authors who doomed it. Despite the August standing both authors seemed to grant the Necessary Law – seeming to place it atop a hierarchy of sources of International Law, and making it inviolable and unchangeable – its force was only moral, binding only in foro interno. In their accounts, it was paradoxically absolutely binding, absolutely unchangeable, and absolutely (humanly) unenforceable (Wolff Reference Wolff1749: Prolegomena, Sections 4–6; Vattel Reference Vattel1758: Introduction, Sections 7–9). Nonetheless, the parallels with contemporary understandings of jus cogens are readily apparent; both the jus necessarium and rules of jus cogens status are absolute and non-derogable.

The primary differences between the two lie in the attribution of changelessness to the rules of the Necessary Law and the enforceability of modern rules of jus cogens (Christenson Reference Christenson1988, 612; Byers Reference Byers1997, 224). The laws of nature were understood definitionally to be timeless and unchangeable. The moral laws of nature were regarded as every bit as immutable as the physical laws of nature. What was morally right or wrong was no more variable across place or time than gravity or magnetism. Rules of jus cogens status possess the same categorical character as those of natural law, but because they are contingent human creations, and the categorical character of the obligations they impose is human created, they can be changed by other human acts – as is specified in the final clause of Article 53 of the Vienna Convention.Footnote 5

Alfred Verdross reintroduced the concept of categorical obligation to modern International Law in his 1937 essay ‘Forbidden Treaties in International Law’ (Verdross Reference Verdross1937, 571–77). In a starkly framed challenge to the regnant forms of positivism and voluntarism of the time, Verdross rejected the contention held by ‘those authors who base the whole international law on the agreement of the wills of the states’ that ‘states are free to conclude treaties on any subject whatsoever’ (Verdross Reference Verdross1937, 571–72). Rozakis’ much later assessment of the orthodox doctrine is more blunt still ‘States were unconditionally free to conclude agreements of whatever content, even if contrary to already general rules of law’ (Rozakis Reference Rozakis1976, 3). By contrast, Verdross found in the general principles of law shared by all legal systems a public order prohibition against agreements contra bonos mores, and concluded that because international law counted among its sources ‘general principles of law recognized by civilized nations’ that this rule applied to prohibit immoral treaties.Footnote 6 Verdross’ efforts are important because he represents someone who, while working primarily within a positivist context, introduced explicitly moral concerns into the law of treaties, because he was a positivist uncomfortable with the stringency of the then-dominant voluntarism.

Verdross’ concern was treaties ‘which restrict the liberty of one contracting party in an excessive or unworthy manner or which endanger its most important rights’ (Verdross Reference Verdross1937, 574).Footnote 7 For Verdross, an immoral treaty was one that prevented a state from performing any of the functions that he identified as the ‘moral tasks of states’: maintenance of domestic order, national defense, ‘care for the bodily and spiritual welfare of citizens at home’ and protecting citizens while abroad (Verdross Reference Verdross1937, 574). Although this is a rather narrow understanding of morality, simply by arguing for the inclusion of such concerns, by arguing for moral limitations on the freedom of contract, Verdross was issuing a prescient challenge to the dominant, stark understanding of voluntarism as well as to the concomitant understanding of sovereignty.

In Verdross’ treatment, any treaty constructed to have such immoral effects would be void on its face, and would not give rise to any obligations – at least no obligations relating to the portions of the treaty with unlawful/immoral content – there would therefore be no need for the treaty to be voided. Interestingly, however, Verdross held that should a tribunal declare an immoral treaty to be void, their finding would have ‘no constitutive, but simply a declaratory character; [the finding] states that no obligation with such contents has ever come into existence’ (Verdross Reference Verdross1937, 577). This oversimplifies matters. By conflating the type of speech act and its perlocutionary effect, Verdross missed the constitutive effect of declaring a treaty void.

While his aprioristic understanding of the invalidity of immoral treaties is a sensible reaction to the ‘pseudo-positivistic doctrine which denies the prohibition of immoral treaties’, he missed the fact that even if declaring a treaty void was not what made it void, it nonetheless reinforces the fact of its invalidity (Verdross Reference Verdross1937, 576). Even if the invalidity of the treaty came solely from its immorality – ignoring the human-centeredness of Verdross’ own account of morality – a declaration that the treaty was void because contra bonos mores would both reinforce the strength of the specific moral norm violated and reinforce the rule that immoral agreements are void.

Verdross’ invocation of a class of rules that sets the standard for the allowability of other rule candidates gives us some indication of why even within positivism concern arose that there be a class of rules that be treated as indefeasible. However, in contrast to Dubois’ enlistment of him as a fellow natural law theorist, Verdross was operating in this regard within the positivist tradition (Dubois Reference Dubois2009, 143). We see this most clearly in his mobilization of ‘general principles of law’ – one of Positive International Law's recognized sources of obligation – as evidence of the prohibition of treaties contra bonos mores rather than resorting to some source exogenous to the human will.Footnote 8 It is telling that Verdross limited himself to a source pedigree-approved by positivism. More important than this exegetical quibble, however, is the way that Verdross’ early efforts signal a marked divergence from the stringency of, for example, the Austinian understanding of positivism and its famously rigid partition of law and morality, but it is a divergence from within.

Jus cogens was brought into Positive International Law by positivists for many of the reasons announced by Verdross: there was a sense that there needed to be moral limitations on the right of contract in international law. Almost immediately, this view expanded beyond simply a rule governing the law of treaties to the idea that there is a range of categorical prohibitions on state actions. It is widely agreed that the ambit of jus cogens extends beyond treaties, and that any act that is in conflict with a norm of jus cogens is invalid. ‘If all treaties in conflict with a peremptory norm are prohibited and, consequently, all acts based on such treaties are unlawful, it seems evident that the outcome is the comprehensive prohibition of all acts contrary to peremptory norms’ (Hannikainen Reference Hannikainen1988, 6, 201).

Many commentators trace the introduction of jus cogens to the international community's reaction to events surrounding World War II (Janis Reference Janis1988, 361; Criddle and Fox-Decent Reference Criddle and Fox-Decent2009). A number of representatives at the Vienna Conference also brought up the issue of why jus cogens was being introduced to international law at that particular point in time. As stated by Mr. Yapobie, the representative of the Ivory Coast:

Mr. Dadzie of Ghana gave a similar interpretation:

These two statements mark out a clear set of North–South concerns; Cassese also noted this thread, especially as it was marked out in the statement of Mr. Cole, the representative from Sierra Leone, who noted that the inclusion of jus cogens, in the Vienna Convention ‘provided a golden opportunity to condemn imperialism, slavery, forced labor, and all practices that violated the principles of the equality of all human beings and of the sovereign equality of states…’ (United Nations Conference on the Law of Treaties, 1st Session 1969, 300).

The matter was approached rather differently by Mr. Dons of Norway:

Categorical obligations returned to positivist international law, despite positivism's general discomfort with them, because international society, that is, states, determined that there was a set of issues – even if no definitive list has ever been recognized – that required rules that would be exceptionless and non-derogable. Lacking any such notion in its own conceptual repertoire, positivism borrowed from natural law. It did so, however, only on terms with which the concepts could be made to fit within its voluntarist conceptual framework and voluntarist political sensibilities.

Categoricals in a voluntarist setting

Some at the Vienna Conference indeed conceptualized jus cogens in Naturalist terms. ‘Some states or writers maintain that it has been imposed on states as a consequence of natural law, having its source in human nature or emanating from a divine source and so being independent of the will of states’ (Paul Reference Paul1971, 29). In the words of P.M. Dupuy, the Vatican's representative, the Vienna Convention ‘sanctioned the “positivization” of natural law’ (Bianchi Reference Bianchi2008, 492). Relatively few states’ representatives held this position, however; of those representatives expressing any view on the source of jus cogens’ categorical obligation whatsoever, only four (Mexico, Italy, Ecuador, and Monaco) asserted any basis in natural law, but in contrast to Danilenko's assertion, none of the four unequivocally rooted jus cogens in natural law (Danilenko Reference Danilenko1991, 44).

Although some representatives to the Vienna Conference may have been thinking of jus cogens in Naturalist terms, it is clear from the report of fourth Special Rapporteur, Sir Humphrey Waldock, that in its drafting work before the conference, the International Law Commission ‘based its approach to the question of jus cogens on positive law much more than on natural law’ when drafting the preliminary versions of what became Articles 53 and 64’ (United Nations Conference on the Law of Treaties, 2nd Session 1969, 327; Yarwood Reference Yarwood2006). While four states’ representatives posited some relationship between jus cogens and natural law, 13 representatives placed the former squarely within the realm of positive law. These statements were unequivocal assertions, and some (Turkey, Hungary, Brazil) also made starkly voluntarist assertions about all international legal obligation being rooted exclusively in state consent. The declaration of Mr. Bokor-Szegö, the representative from Hungary, is representative ‘The source of rules having a peremptory character, like all other rules of international law, lay in the will of states’ (United Nations Conference on the Law of Treaties, 2nd Session 1969, 311. Emphasis added).Footnote 10

If the majority at Vienna were correct, then jus cogens as it exists in contemporary international law comes to little more that states agreeing to act as if certain norms were indefeasible, and agreeing to bind themselves categorically to those norms. If the Naturalist minority were correct, a number of difficult to explain consequences might arise; foremost among them would be the existence of a class of norms not dependent upon state consent – that is to say, a class of norms inexplicable in the language game of positivist voluntarism.

The question of consent is central to clarifying the relationship between jus cogens and positivist voluntarism, but there are actually multiple issues wrapped up in the question. There is the initial issue about consent-to-be-bound: do the normal secondary rules rooting obligation in consent not apply to rules of jus cogens character? There is also a posterior but distinct question about consent-to-remain-bound. The first question involves the imposition of obligation – can rules of jus cogens standing be imposed upon the unwilling, upon the non-consenting? The logic of the positivist–voluntarist tradition and related state practice reject such a notion, but we do find scholarly arguments (surveyed below) that jus cogens transcends positivist–voluntarist metanorms. The second issue, consent-to-remain-bound, confronts similar issues, but here, as we shall see below, although positivist–voluntarist doctrine rejects a limitation on the state's freedom to renounce, there is not a correlative resistance to be found in state practice. States resist the idea of the imposition of obligation, and doctrine both reflects that policy preference and sets a limit on practice.Footnote 11 States do not, however, seem averse to subjection to a (narrowly defined) class of obligations that cannot be voluntarily shed (at least not unilaterally) once they have been voluntarily accepted.