1. Introduction
The persistent objector rule is well established in the context of customary international law, where it allows a State to avoid being bound by an emerging customary norm if it has consistently and clearly objected during the formation of that norm.Footnote 1 Such objection must be persistent, unambiguous and timely,Footnote 2 and the rationale for the rule lies in preserving State consent, given that silence is generally treated as acquiescence.Footnote 3 In this sense, the rule operates as a mechanism that preserves a voluntaristic foundation of custom, while it also functions in practice as a bargaining tool through which States may resist, influence or shape emerging norms. However, continued reliance upon the rule has become more contested in light of the growing importance of communitarian norms in international law, which are norms owed to the international legal community as a whole, in respect of which all States may have standing to invoke compliance.Footnote 4 This development may, in practice, limit the space for persistent objection.Footnote 5
Despite its doctrinal prominence, the persistent objector rule has only received sustained scholarly attention in the last 60 years, and its very existence as a principle of international law remains debated.Footnote 6 As Green notes, the term itself only entered international legal discourse in the 1960s through Ian Brownlie’s Principles of Public International Law. Footnote 7 While earlier writings from the seventeenth and eighteenth centuries describe certain forms of State objection that resemble aspects of the modern doctrine, they do not fully reflect the current structure or requirements.Footnote 8 Bradley and Gulati argue that, although something akin to the rule existed before 1945, its systematic linkage to customary international law emerged only after 1945, and more clearly from the 1970s onwards.Footnote 9
This historical evolution suggests that the persistent objector rule is best understood as a manifestation of a broader voluntarist approach to international law,Footnote 10 allowing States to opt out of developing legal obligations. Importantly, however, it also raises a conceptual question that has received little attention in the literature, namely, whether the rule is inherently tied to customary international law, or whether it might, in principle, extend to other sources of unwritten international law, in particular general principles of law (GPLs).
This question has recently emerged in the work of the International Law Commission (ILC) on GPLs, but it has not been the subject of sustained doctrinal analysis. Existing scholarship has largely assumed the rule’s confinement to custom, without systematically examining its applicability to GPLs.Footnote 11 This article addresses that gap.
Before doing so, it is necessary to clarify certain misconceptions in the literature. Some authors have suggested that the United States (US) played a central role in developing or even consolidating the doctrine of the persistent objector. For instance, Dumberry argues that ‘although the concept of persistent objector can be traced back to more than 50 years ago, it only truly emerged as a coherent theory some 20 years ago when it was embraced by the United States’.Footnote 12 This statement may be misleading for several reasons.
First, as explained above, the rule has a much longer history. While the doctrine may be relatively ‘new’, elements of a coherent doctrine can be traced back more than 20 years, albeit not in a fully developed form before 1945. Second, although it may be true that the US has invoked the rule before international courts and tribunalsFootnote 13 more than other States, making it the biggest ‘user’ and arguably ‘abuser’ of the rule, it is inaccurate to suggest that the US created the rule. As this article will show, it is indeed the US that has initiated calls to extend the persistent objector rule to GPLs. However, the statement implies that the persistent objector rule was somehow established by the US and is a uniquely American doctrine. This is not entirely correct, as numerous other States have invoked the rule since the establishment of the United Nations (UN).Footnote 14
Against this background, the article argues that although the historical development of the persistent objector rule leaves open the theoretical possibility of extending it beyond customary international law, such an extension is ultimately neither conceptually coherent nor functionally appropriate in the context of GPLs. The core argument is that the persistent objector rule is grounded in a framework of consent-based norm formation, whereas GPLs do not operate on the same consensual logic. As a result, the rule does not translate into the architecture of GPLs. To substantiate this claim, the article tests the applicability of the persistent objector rule across three case studies: domestic, international and regional GPLs. Regional GPLs in this context encompass also subregional GPLs, such as those formed within the European Union (EU) as a regional organisation, and the Andean Community as a subregional organisation. Bilateral GPLs are not examined.
The article proceeds as follows. Section 2 outlines the definition and formation of GPLs (Section 2.1), before tracing the emergence of the persistent objector rule in the ILC’s work and examining how it was discussed by the Commission’s members (Section 2.2) as well as the relevant debates in the UN Sixth Committee (Legal) (Section 2.3). Section 3 then addresses the central research question: whether the persistent objector doctrine applies to GPLs. It first develops a conceptual account of GPLs and the limited role State consent plays in their establishment (Section 3.1), before examining whether the persistent objector rule could operate in relation to domestic GPLs (Section 3.2), international GPLs (Section 3.3), and/or regional GPLs (Section 3.4). Section 3.5 offers a more conceptual reflection on compatibility and utility, drawing on Green’s analytical framework. Section 4 concludes that the persistent objector rule does not apply to GPLs, whether domestic, international or regional, and that attempts to extend it to this domain are conceptually and functionally misplaced.
2. GPLs and the persistent objector rule
The question of whether the persistent objector rule applies to GPLs has only been raised recently. Before examining the views of ILC members and the comments made by States in the UN Sixth Committee (Legal) on this issue, it is first necessary to establish what GPLs are.
2.1. Defining GPLs
According to Article 38 of the Statute of the International Court of Justice (ICJ Statute), GPLs constitute the third formal source of international law after treaties and customary international law.Footnote 15 Like custom, they are an unwritten source of law.
In order to consider whether GPLs are susceptible to persistent objection, it is first necessary to analyse how this source is generated. Draft Conclusion 3 of the ILC work on GPLs provides that they may be derived from national legal systems (paragraph (a)), also referred to as the first category of GPLs or general principles in foro domestico, or they may be formed within the international legal system (paragraph (b)), known as the second category of GPLs.Footnote 16 For the former, the identification process is set out in Draft Conclusions 4–6. Draft Conclusion 4 requires the identification of a principle as common to the various legal systems of the world (further elaborated in Draft Conclusion 5), while Draft Conclusion 6 provides that such a common principle may be transposed into the international legal system if it fulfils a regulatory purpose and is compatible with international law.Footnote 17
Under this framework, Draft Conclusion 5 requires a comparative analysis of different legal systems across regions, ensuring that the identified principle is sufficiently representative.Footnote 18 Domestic legal principles thus serve as the substratum of general principles in foro domestico. Once a principle can be identified across various legal systems, whether in case law, legislation or domestic custom, it is said that it is recognised within those systems. It is sufficient that a principle be found across several regions of the world; exhaustive surveys of every individual State are not required.Footnote 19
Under Draft Conclusion 6, a commonly recognised principle may be transposed into the international legal system where it serves a regulatory function and is compatible with existing international law.Footnote 20 In this sense, the recognition element is implicit, meaning that it is assumed to have been transposed. This transposition may be established where the principle is used in international law, for example, in pleadings, diplomatic correspondence and reports of intergovernmental or international organisations, although such transposition may be rebutted.Footnote 21
For principles formed within the international legal system, identification depends on their intrinsic character within that system.Footnote 22 This ‘intrinsic’ element may be understood as referring to principles essential to the operation of the international legal order, such as the rule that municipal law does not prevail over international law,Footnote 23 and is evidenced deductively and inductively through all available evidence, treaties, resolutions, systemic reasoning, judicial and institutional practice.
A third category of GPLsFootnote 24 may be those formed within regional or subregional legal systems, which the ILC described in Draft Conclusion 12 as having a limited scope of application ratione personae.Footnote 25 Accordingly, GPLs may arise from domestic, international and regional or subregional legal systems. All three categories will be assessed against the persistent objector rule in Section 3.
These formation methods also highlight a key distinction between custom and GPLs: the former requires State practice and opinio juris, whereas the latter require only the ‘recognition’ of a principle by the community of nations, either through domestic legal systems or within the international legal system itself.Footnote 26 The ‘recognition by the community of nations’ is key for GPLs. Thus, GPLs require only positive ‘recognition’ of a principle in order to exist, rather than ‘acceptance’ of a ‘general practice as law’. By contrast, the Military and Paramilitary Activities in and against Nicaragua judgment stated that ‘the mere fact that States declare their recognition of certain rules is not sufficient for the Court to consider these as being part of customary international law’.Footnote 27 This suggests that mere recognition may be sufficient to indicate the existence of a GPL, but not of a rule of customary international law. Hence, arguably GPLs have a lower threshold to be identified than custom.
The purpose of GPLs is to reflect the systemic importance of protecting community interests, underpinning rulesFootnote 28 and addressing specific gaps in the international legal system.Footnote 29 In other words, they serve to complete the law, facilitate legal reasoning,Footnote 30 promote coherenceFootnote 31 and, in some instances, provide a basis for primary obligations.Footnote 32 In practice their purpose is mainly as subsidiary sources to interpret treaties and custom, which arguably explains their lower threshold for identification.Footnote 33
Relatedly, GPLs are a formal source of international law,Footnote 34 comparable to treaties and customary international law. All three sources possess legal authority. The conceptual approach adopted in this article does not reduce them to material or interpretative sources of international law, as this would place them on a par with the subsidiary means listed in Article 38(1)(d) ICJ Statute, such as the writings of leading scholars and judicial decisions. Scholarly writings and judicial decisions are material sources through which the law may be identified, but they do not themselves confer legal authority. Rather, material sources serve evidentiary and interpretative functions in relation to formal sources of international law. Accordingly, this article disagrees with Weil, who concluded that GPLs constitute only material sources and not formal sources of international law.Footnote 35
Regarding their nature, there was a historically a schism during the deliberations of the Advisory Committee of Jurists in 1920 between competing conceptions of GPLs: Elihu Root’s positivist approach and Baron Descamps’ natural law approach.Footnote 36 The current formulation of Article 38(1)(c) ICJ Statute represents a compromise between these two perspectives. As a result, the foundation of GPLs lies at the boundary between positivism and natural law, precisely because they were designed to enable the legal system to reach beyond existing rules when those rules prove insufficient.
The natural law dimension of GPLs has at times been criticised as overly open-ended and susceptible to judicial activism.Footnote 37 While this article acknowledges those concerns, it argues that the delicate balance embodied in Article 38(1)(c) should not be displaced. The relative weight of positivist and natural law elements depends on the type of GPL under consideration. Some principles, particularly those that are newly formed, may be more firmly grounded in positive law if actively created by the community of nations, whereas others, especially those inherent in the very concept of law, may reflect a stronger natural law foundation.Footnote 38
2.2. ILC discussion on the persistent objector rule in relation to GPLs
The debate on whether the persistent objector rule can be applied to GPLs started with the comments and observations submitted to the ILC in early 2025, where the US argued that ‘the Commission should also consider that a State might maintain a persistent objection to the recognition of a general principle of law similar to the way it might do so with respect to a rule of customary international law’.Footnote 39 The US attempted to interpret the ‘recognition’ criterion for the existence of GPLs under Article 38(1)(c) ICJ Statute as equivalent to the ‘acceptance’ necessary for the establishment of customary international law. In other words, this would raise the threshold for the formation of GPLs. Given the US’ long-standing scepticism towards GPLs,Footnote 40 such a position is unsurprising.
As a result of these comments by the US, the Special Rapporteur on General Principles of Law, Marcelo Vázquez-Bermúdez, addressed the issue of persistent objection in his Fourth Report, which was discussed during the ILC’s seventy-sixth session in May 2025.Footnote 41 The Fourth Report sought to address governments’ comments and observations on the Draft Conclusions and Commentaries, adopted at the first reading at the seventy-fourth session in 2023, by proposing responses and amendments to the Draft Conclusions.Footnote 42 He noted that there is neither State practice nor scholarly literature to support the proposition that the persistent objector rule applies to GPLs.Footnote 43 He further observed that the formation of GPLs is more diffuse than that of custom, making it difficult for a State to maintain a persistent objection.Footnote 44 He emphasised that, with respect to domestic GPLs transposed onto the international plane, the process of transposition itself acts as a strong filter, rendering the application of a persistent objector rule unnecessary.Footnote 45 In this context, the filtering mechanism refers to the requirement that principles must not conflict with existing international law in order to be transposed, meaning that only compatible principles may become part of international law. Curiously, however, the Report did not specifically address GPLs formed within the international legal system itself, the reason for which remains unclear.
In light of the State comments and the Special Rapporteur’s engagement with them in the Fourth Report, the issue emerged as a point of discussion in both the Plenary and the Drafting Committee at the ILC’s seventy-sixth session in May 2025. Two distinct camps could be identified in the plenary session. The first camp comprised five members who supported further consideration of whether the persistent objector rule applies to GPLs. Patel (India) argued that the topic warranted deeper analysis in relation to GPLs formed within the international legal system. He referred to the ILC’s work on Immunities of Foreign State Officials in Criminal Jurisdictions,Footnote 46 where the ‘principle’ of universal jurisdiction, though not framed as a ‘general principle’, was contested by States in the Sixth Committee (Legal). Citing the Arrest Warrant case, in which Judges Higgins, Kooijmans and Buergenthal highlighted the divisions over universal jurisdiction,Footnote 47 Patel contended that the matter has ‘real practical importance’.Footnote 48 He also referenced the United Kingdom’s (UK) statement noting a ‘lack of international consensus’ on universal jurisdiction,Footnote 49 which again conflates custom with GPLs and treats GPLs as purely voluntary.Footnote 50
Zagaynov (Russia) characterised the issue as ‘unresolved’, given the absence of practice or doctrine.Footnote 51 He recalled Fernandes’ remarks at the Permanent Court of International Justice (PCIJ) Advisory Committee of Jurists that principles applied when ‘before the dispute, [they] were not rejected by the legal traditions of one of the States concerned’.Footnote 52 While he wondered whether this implied a form of persistent objection,Footnote 53 it may be better to interpret Fernandes’ statement as indicating that principles play a residual role when treaties and custom are silent. Zagaynov also offered a hypothetical scenario: if the principle of the common heritage of mankind (a GPL of the second category, recently embedded in the Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (BBNJ Agreement)) were to crystallise into custom, a State objecting to the customary rule might nonetheless be bound by the GPL.Footnote 54 This, he suggested, would create a tension between sources, but he conceded that such concerns remain largely theoretical.
Akande (UK) also supported applying the persistent objector rule to GPLs, particularly those of the second category. He invoked the principle of State consent as a foundational GPL of the international legal system and argued that States should be able to withhold consent to the recognition of such principles.Footnote 55 In his view, the persistent objector rule would therefore apply to GPLs of the second category, but not to domestic GPLs, which are already being filtered out during their transposition to the international level.Footnote 56
Paparinskis (Latvia) focused on international investment law. He referred to the principle of proportionality, sometimes characterised as a ‘regional’ GPL, particularly in the European context, and its incorporation into Occidental v Ecuador (II) under the fair and equitable treatment standard.Footnote 57 In that case, the tribunal noted proportionality’s origins but did not confront any State objections.Footnote 58 Paparinskis further observed that the US has repeatedly resisted the incorporation of proportionality into fair and equitable treatment in Investor-State Dispute Settlement (ISDS) cases, such as Adel A Hamadi Al Tamimi v Oman, where it argued that State practice and opinio juris do not support such an obligation.Footnote 59 This opposition, however, appears to be directed at a proposed interpretation of a treaty or customary international law, rather than at a GPL itself.Footnote 60
Asada (Japan) noted the difficulty of envisioning a situation in which the persistent objector rule would not apply to GPLs but would apply once the same principle crystallised into custom.Footnote 61 He therefore suggested that the persistent objector rule could also apply to GPLs.
The second camp comprised other members of the Commission who disagreed with the inclusion of the persistent objector rule in relation to GPLs in the draft conclusions. Galindo (Brazil) stressed the absence of any supporting practice.Footnote 62 Ridings (New Zealand) considered the rule applicable only to the formation of customary international law and thus irrelevant to GPLs.Footnote 63 Grossman Guilloff (Chile) argued that the matter should be addressed in the commentaries rather than the draft conclusions themselves. Oyarzábal (Argentina) raised a query regarding the relationship between GPLs and customary international law, noting that certain concepts were applicable to both, yet the persistent objector rule appears not to encompass GPLs.Footnote 64
As these debates reveal, there remains division within the ILC on this issue. Notably, members from powerful States have been most active in advocating for the extension of the persistent objector rule to GPLs, a move that risks distorting the delicate balance between the sources of international law. A possible explanation for this point, viewed from a realist perspective, is that powerful States seek to preserve maximum control over the legal obligations by which they are bound, which the persistent objector rule provides for.
2.3. UN Sixth Committee consideration
In the most recent eightieth session of the UN Sixth Committee (Legal) in October 2025, only a limited number of States commented on the ILC’s decision not to include a conclusion on the persistent objector rule in the work on GPLs. Some States agreed with the Commission’s approach,Footnote 65 others disagreedFootnote 66 and some requested clarification as to what happens when a State opposes the formation of a GPL.Footnote 67 It is thus clear that the ILC and States are divided on this issue. The following sections will therefore examine more closely whether the persistent objector rule can, or should, apply to GPLs, and will seek to offer some tentative answers to this unresolved question.
3. Can the persistent objector rule apply to GPLs?
The central question apparent from the discussions within the ILC is whether the persistent objector rule is applicable to GPLs. To examine this issue, the analysis is divided into five sections. Section 3.1 highlights that the role of consent in the formation and application of GPLs may be limited. The aim of this section is to provide the conceptual and theoretical foundation on which this article is built. The article then tests the main research question through three case studies. Section 3.2 argues that the persistent objector rule is inapplicable to GPLs derived from domestic legal systems, emphasising that they will not emerge without broad recognition across various legal systems. Section 3.3 similarly contends that the persistent objector rule does not apply to GPLs formed within the international legal system and advances four arguments in support of this conclusion. Section 3.4 further argues that, in relation to the ILC’s new category of GPLs with a limited scope of application, i.e. regional or subregional GPLs under Draft Conclusion 12, the persistent objector rule is irrelevant. These principles already exist when they are applied in another regional legal system; the issue is therefore one of the reception of foreign legal principles rather than of persistent objection. Following these case studies, Section 3.5 turns to practical considerations, using Green’s analytical framework to assess whether the rule has any utility with respect to GPLs. It concludes that the rule, which safeguards positive law—namely custom—is of limited practical use in this context. It is incapable of influencing the formation or application of GPLs, and there is no evidence to support its application to them.
3.1. The role of State consent may be limited
Before turning to the three case studies that test the applicability of the persistent objector rule, this section first introduces the author’s conceptual and theoretical framework. It argues that State consent plays only a limited role in relation to GPLs, which occupy a position at the intersection of positive and natural law. Because of this hybrid nature, GPLs are difficult to reconcile with the persistent objector rule, which was developed to safeguard a source of international law—custom—that is grounded in a more strongly voluntarist conception of State consent. This section is divided into two parts: first, it examines the argument that unanimity or near-unanimity leaves no room for objection; second, it addresses more specifically the relationship between State consent and GPLs.
3.1.1. Requirement of unanimity or near-unanimity leaves no room for objection
From a historical perspective, GPLs were thought to require unanimous or quasi-unanimous support, thus leaving no scope for objection. The procès-verbaux of the PCIJ Advisory Committee of Jurists indicates that the committee members discussed the view expressed by de Lapradelle, who noted that ‘the only generally recognised principles which exist, however, are those which have obtained unanimous or quasi-unanimous support’.Footnote 68 The underlying logic for accepting quasi-unanimous support is that, otherwise, a tiny handful of States (or even a single State) could veto the emergence of a GPL. Given the diversity of domestic legal systems, it would be nearly impossible to find the exact same GPL in every single jurisdiction. This would make the recognition of GPLs derived from domestic legal systems extremely restrictive. Similarly, in its Advisory Opinion on Reservations to the Genocide Convention, the International Court of Justice (ICJ), referring to the plural language of Article 38(1)(c) ICJ Statute, stated that the Genocide Convention contained ‘principles which are recognised by civilised nations as binding on States, even without any conventional obligation’,Footnote 69 not ‘a civilised nation’ in the singular. The emphasis, therefore, is on recognition by a plurality of nations rather than by a single State.
This is also acknowledged by the ILC in Commentary 4 to Draft Conclusion 5, which states that GPLs must be ‘sufficiently’ widespread but need not be universal.Footnote 70 A restrictive approach, where a GPL would only be recognised if it were unanimous, has been criticised, notably by Jain, who highlighted that judges at the International Criminal Tribunal for the former Yugoslavia (ICTY) struggled to identify principles universally recognised by States.Footnote 71 For example, the ICTY faced difficulties determining the defence of duress and whether sexual oral penetration constituted rape or sexual assault, as each domestic legal system had its own approach.
3.1.2. The limited role of State consent in GPL formation
As noted in Section 1, the persistent objector rule exists in part to preserve voluntarism and the consensual framework of customary international law. Interestingly, at the eightieth session of the UN Sixth Committee (Legal), several States called on the ILC to ensure that GPLs are grounded in State consent.Footnote 72 This raises the question whether GPLs are consensual in nature, which is yet another question unresolved by the ILC. This section aims to answer it. If GPLs are consensual, the persistent objector rule may apply; if they are not, then the rule cannot apply. As the title of this section suggests, it is argued that GPLs are not dependent on States’ consent for their formation.
Three possible submissions might be advanced in relation to consent and GPLs. First, the voluntarist theory that rules are binding only if States have agreed to them is flawed, and GPLs create binding law without express consent.Footnote 73 Second, GPLs are only a material or interpretive source of law and therefore do not require consent, being equivalent to the sources in Article 38(1)(d). Third, the voluntarist theory is correct and GPLs create law, meaning that consent is required and therefore either the persistent objector rule must apply or GPLs can only be created unanimously.
This section argues that the first option is the correct one, namely, that GPLs can create binding law without the express consent of States, and that the other two options must therefore be rejected. The eminent judge Cançado Trindade supports the first proposition, arguing that consent is not needed for GPLs as they are ‘guarantors of the legal order itself, of its unity, integrity and cohesion’.Footnote 74 It is also clear that the second proposition is incorrect because GPLs are not merely material or interpretative tools but, rather, ‘a source of international law’, as stated in Draft Conclusion 1.Footnote 75 Draft Conclusion 10(1)(a) further clarifies that GPLs may serve as the basis of primary rights and obligations.Footnote 76 The third proposition clearly does not reflect reality, as GPLs are not consent-based, and do not require unanimity, as Section 3.1.1 has clarified, noting that near-unanimity suffices. There is support among scholars for this approach. Heller posited that:
Like all law, international law is the product of a community of culture and interests … it depends on the intensity of this community whether it succeeds at all in objectifying … fundamental legal principles, and whether … the fundamental legal principles prove to be sufficiently effective to be positivized by states’ act of will into rules of international law.Footnote 77
He goes on to state that ‘the only thing standing above the sovereign unit of will is, necessarily, fundamental legal principles’,Footnote 78 suggesting that certain principles may exist independently of State consent. Arguably, he also implies that principles may crystalise into rules. O’Connell and Day similarly assert that GPLs transcend State will, because their nature is not fully voluntaristic.Footnote 79 Shao submits that recognition in the GPL sense is implied consent, asking ‘what States may have intended’.Footnote 80 Whether ‘implied consent’ involves actual consent is, however, controversial. It may be possible to identify the point at which a State acknowledges a principle, but this could be said of virtually any form of State conduct and is therefore not particularly persuasive. Describing recognition as ‘implied consent’ may stretch the concept too far, particularly since scholars generally characterise custom as being based on ‘implied consent’.Footnote 81 Employing the same concept for GPLs as for custom would blur the distinction between these sources of law and still suggest an element of actual consent. A more convincing view is that recognition denotes some form of acquiescence to GPLs or that the mere articulation of a principle by States, as members of the international legal community, is sufficient to shape their understanding of the contours of that principle. This supports the view that GPLs contain both natural and positive elements.
This view that GPLs—whether extrapolated from domestic or international legal systems—constitute a mixture of positive and natural law was articulated by Judge Tanaka in his dissenting opinion in the South West African (Second Phase) case. He argued forcefully that GPLs extend beyond State consent:
States which do not recognize this principle or even deny its validity are nevertheless subject to its rule. From this kind of source international law could have the foundation of its validity extended beyond the will of States, that is to say, into the sphere of natural law and assume an aspect of its supra-national and supra- positive character.Footnote 82
Using this approach, Alston and Simma have argued that human rights and GPLs ‘conform more closely than the concept of custom to the situation where a norm invested with strong inherent authority is widely accepted even though widely violated’, thereby echoing Judge Tanaka’s position.Footnote 83
In the end, it may be concluded that, because of their hybrid nature at the intersection of natural and positive law, GPLs do not require State consent in the strict sense. Accordingly, State consent plays only a limited role in the existence and formation of GPLs.
3.2. The persistent objector rule is inapplicable to GPLs derived from domestic legal systems
This section addresses the first case study, namely whether the persistent objector rule is applicable to GPLs derived in foro domestico. The central issue concerns the critical number of States that must recognise a principle before it can qualify as a GPL. GPLs will not arise in the absence of broad recognition, thus a principle must be common to a sufficient number of States in order to qualify as a GPL.Footnote 84 The analysis demonstrates that the persistent objector rule has no meaningful role to play, because there is no temporal space in which it can operate. As a preliminary point, the persistent objector rule applies only during the formation of a norm. Once the norm has crystallised, the rule no longer applies. At that stage, a State’s refusal to accept the norm amounts not to an objection to its formation but, rather, to a denial of a preexisting legal norm.
The discussion begins by setting out several basic propositions. It then examines two scenarios in order to test the applicability of the persistent objector rule, drawing comparisons with custom where appropriate to highlight the distinctions between these two sources of law.
Several preliminary propositions should be restated. Most obviously, if a principle is only recognised in one State, it cannot be a GPL, as a single State cannot create a GPL that is binding on all States.Footnote 85 The same is true for custom. However, the absence of a principle in the municipal law of a State does not necessarily indicate that the State objects to it; they may simply see no need for the particular rule, either because a different principle applies or because the legal issue has not arisen.Footnote 86 Thus, a principle does not need to exist in every legal system for it to become a GPL.Footnote 87 This holds true in adjudication where judges do not require principles to exist in every domestic legal system to consider them GPLs.Footnote 88
Having set out some basic propositions concerning the creation of GPLs in foro domestico, scenario 1 illustrates that where a principle is recognised in many States but absent from many others, it cannot be regarded as a GPL.Footnote 89 This point equally applies to custom: the formation of custom does not require every State to engage in the relevant practice or to express opinio juris in its favour, but once the rule emerges it binds all States, subject only to the persistent objector rule. However, it is not deemed persistent objection if a large number of States reject an emerging custom: it will simply not become a rule of customary law. By way of example, if civil law does not accept a principle that common law does, then it cannot qualify as a GPL (though it may be regional) because of lack of recognition of the principle, rather than any persistent objection.Footnote 90
In scenario 2, where a GPL is recognised by many States but absent in a few, the situation becomes more complex. For instance, in his dissenting opinion in the Mexico City Bombardment claims commission—which addressed damage claims caused by the Felicistas Rebels in 1913—Sir John Percival noted that certain maxims were neither part of English nor US law, implicitly suggesting that principles applied by other States cannot qualify as GPLs.Footnote 91 However, if only a minimal number of States are indifferent to a particular rule, a GPL may still be established. It is contextual. The key is to return to the nature of GPLs: they are abstract legal principles derived from the basic structures of legal systems, not specific State conduct. Because GPLs function as structural norms of the international legal order, rather than optional behavioural norms as customary rules do, the persistent objector rule has no application.
As these two scenarios demonstrate, the absence of a principle in domestic legal systems should not be equated with a rejection of that principle. Some scholars may arguably conflate the two. For example, Akehurst suggests that a State may reject a GPL domestically and, as a result, not be bound by it.Footnote 92 He does not explain this assertion. As a counterargument, it is important to underscore that a State cannot reject a principle in its domestic legal system in the same way that it may object to an emerging rule of custom. A principle is either present in the domestic legal system, whether in legislation, case law or local custom, or it is absent. Moreover, it is difficult to see how a State could object domestically to a GPL when it may not know that the principle will, or even might, be transposed to the international level. This is one of the features that renders the persistent objector rule incompatible with domestic GPLs. Presumably, a principle reaches a critical threshold at which it becomes a GPL. Before that point, there is no GPL to which a State could object; after that point, all States are bound by it. Accordingly, there is only a single moment at which a State’s position toward the principle can affect its development, namely, at the point at which the threshold is reached. Objection cannot therefore be persistent in the sense of an ongoing and continuous opposition.
A further question arises: to what extent should States’ negative positions, including all situations in which a State does not actively recognise a GPL, be taken into account in the formation of GPLs? Three brief points may be mentioned. First, GPLs are not dependant on State consent; the negation or absence of a principle in a particular State does not preclude its recognition, since the inquiry seeks to identify principles objectively across legal systems. The same is true of custom. Second, although GPLs are not dependant on State consent, States’ views may influence whether international courts and tribunals are willing to identify them, and pursuant to Draft Conclusion 8 recognition of a principle by international courts and tribunals can play a crucial role in their recognition as a GPL. A good example is provided by the precautionary principle, one of the most controversial environmental law principles. The divergence of State views has left the ICJ unwilling to define its nature, referring to it as both a ‘precautionary principle’ and an ‘approach’, without clarifying its precise legal character.Footnote 93 In short, recognition in adjudication can help to determine the existence of a GPL under Draft Conclusion 8. Where courts are unable to do so as a result of States arguing against the principle, this may undermine the establishment of a GPL. Third, a lack of commonality can undermine the empirical basis for recognition as suggested. On this point, Akehurst observes that even a few statements by States may suggest that principles not universally applied do not qualify as GPLs.Footnote 94
A recent example of how negation of a principle by States may impact recognition of a GPL may be seen in the ICJ Advisory Opinion on the Obligations of States in respect of Climate Change (Climate Change AO), where the US objected to three GPLs: the principle of common but differentiated responsibilities (CBDR), the precautionary principle and the polluter-pays principle.Footnote 95 These three were among the most invoked principles in the proceedings. The US argued that the polluter-pays principle does not constitute an international GPL but, rather, an emerging concept applicable at the national and sub-national levels.Footnote 96 Its main contention was that the principle is economic in nature rather than legal and, therefore, does not satisfy the criterion of being a principle ‘of law’. Nevertheless, it acknowledged that the principle is reflected in numerous environmental treaties as well as in the Rio Declaration.Footnote 97 The US explicitly stated that there is no ‘indication that States have recognized that such a concept has been transposed to the international legal system as a general principle of law’.Footnote 98 This was the only instance in which the US addressed the method of emergence of a GPL. By implication, since no such objection was raised by the US with respect to CBDR or the precautionary principle, it suggests that those two principles may be regarded as GPLs formed within the international legal system. Upholding the US assertion that the polluter-pays principle is not a GPL, the ICJ held that it did not form part of the applicable law, even though it has been implemented at the national level.Footnote 99 The main point is that the ICJ did not deny that the polluter-pays principle is widely recognised, as it states that it is reflected in ‘certain sector-specific treaties and various types of national legislation’.Footnote 100 Hence, the requirement under Draft Conclusion 5 has been fulfilled. However, the polluter-pays principle fails to satisfy Draft Conclusion 6, namely the transposition of the principle into general international law. The Court noted that the principle is absent from climate change treaties and does not apply ‘directly in the relations between States without having been specified in a treaty’,Footnote 101 even citing the Rhine Chlorides case relied upon by the US.Footnote 102 This was not an example of the Court endorsing the persistent objector rule. Rather, it concluded that there was insufficient evidence to recognise the polluter-pays principle as a GPL that has been transposed onto the international level, thus arguably confining it to a regional, rather than universal, principle. Thus, State positions, including the negation of a principle, are not formally determinative of the existence of a GPL and are therefore not relevant to the operation of the persistent objector rule. The case merely showed that a principle which exists in specialised fields raises questions about the appropriateness or compatibility of its application between States at the universal level. However, in practice, widespread or strong opposition by States can undermine claims of ‘generality’ in the sense of reflecting principles recognised across legal systems, or it may discourage international courts or tribunals from endorsing them. Thus, while negation is not decisive, it remains influential in practice.
This section has shown that, for a domestically-derived GPL, the persistent objector rule does not apply. It demonstrated this through two scenarios: in scenario 1, if a GPL is recognised in many States but also absent in many others, it cannot be considered to exist as a GPL. In scenario 2, where a GPL is recognised by many States but absent in a few, the GPL will exist. This is because of the key requirement that recognition must be sufficiently widespread. The analysis further showed that there is a critical point at which a principle becomes a GPL, and before that point it cannot be objected to, since it is not yet known whether it will crystallise as a GPL on the international plane. Lastly, the example involving the US does not reflect a persistent objection to the polluter-pays principle, given that the principle is already established. Rather, it concerns objections to its appropriateness for transposition into general international law.
3.3. The persistent objector rule is inapplicable to GPLs formed within the international legal system
All of the points made in relation to domestically-derived GPLs apply equally to GPLs derived from the international legal order. However, it must be recalled that, according to Draft Conclusion 7 of the ILC’s work on GPLs, such principles must be intrinsic to the international legal system as such, which is more communitarian in nature than those emerging at the domestic level. Unlike domestic GPLs, the comparativist method operates differently:Footnote 103 to determine whether a principle is intrinsic to the international legal system, all available evidence must be assessed, including principles underlying treaties, resolutions or declarations. As such, the formation process is more homogenous, rather than a patchwork of development across various States.
The following four main arguments are advanced to show that the persistent objector rule does not apply to international GPLs. First, the analysis considers the ILC’s previous work on sources of international law, in particular its work on the Identification of Customary International LawFootnote 104 and on Peremptory Norms of General International Law,Footnote 105 both of which explicitly addressed the persistent objector rule in separate draft conclusions.Footnote 106 In this context, the treatment of the rule in relation to customary international law is relatively uncontroversial,Footnote 107 as it has long been recognised in State practice and invoked in pleadings before the ICJ.Footnote 108 Draft Conclusion 15(1) on the Identification of Customary International LawFootnote 109 explicitly mentions the persistent objector rule and sets out the criteria for its invocation.Footnote 110 Given the settled nature of the rule in the context of custom, the analysis focuses primarily on the ILC’s work on peremptory norms, whose communitarian character closely resembles that of GPLs and, therefore, offers a more relevant point of comparison (Section 3.3.1). Second, it argues that there can be no derogation from fundamental norms, as this would contradict their intrinsic nature within the formation process (Section 3.3.2). Third, it submits that the application of the persistent objector rule to international GPLs would undermine the international legal system as a whole (Section 3.3.3). Finally, it notes that only the US has arguably invoked the persistent objector rule, which it did in its pleadings in the Climate Change AO, an argument with which the ICJ did not engage (Section 3.3.4).
3.3.1. Similarity to jus cogens as communitarian norms?
As touched upon above, GPLs are communitarian in nature, which suggests a similarity with the ILC’s work on peremptory norms, a communitarian category of norms recognised by the international community from which no derogation is permitted. The ILC stated explicitly in Draft Conclusion 14(3) that ‘the persistent objector rule does not apply to peremptory norms of general international law (jus cogens)’.Footnote 111 The reason for this approach is straightforward as the status of a peremptory norm ‘flows from both the universal application and hierarchical superiority’, leaving no room for the persistent objector rule.Footnote 112 Therefore, one might argue that because both GPLs and jus cogens are communitarian in nature, they should be treated in the same way with respect to the persistent objector rule. Jus cogens norms possess a higher normative force and therefore override persistent objection.Footnote 113 Although it has been argued that France was an ‘objecteur persistant’ in the 1960s with respect to jus cogens norms, based on its comments at the 1968–1969 Vienna Conference on the Law of Treaties,Footnote 114 this view is misleading. France was not objecting to the existence of jus cogens norms but, rather, to the lack of a clear process for determining them. It indicated that it would have no objection to the ILC’s approach in its work on the law of treaties, including the limited examples provided, which recognise that treaties conflicting with jus cogens are void.Footnote 115 However, France did object to the way in which jus cogens was reflected in Article 53 of the Vienna Convention on the Law of Treaties (VCLT),Footnote 116 which defines jus cogens and sets out a method for the identification and formation of such norms. In particular, France feared that jus cogens norms could be created without State consent, for example, through treaties or UN General Assembly resolutions.Footnote 117 Greater weight should, therefore, be afforded to France’s contemporary position, which does not object to jus cogens.Footnote 118 Furthermore, from a natural law perspective, jus cogens are also value-based in an ethical sense. By contrast, GPLs are not hierarchically superior in the way jus cogens norms are and they are not inherently value-based (at least not in an ethical sense). Hence, the argument that GPLs share communitarian features with jus cogens and, therefore, the persistent objector rule should automatically not apply to them, may be too much of a stretch. Nonetheless, this similarity does indicate that norms recognised within the community of nations have a more diffuse character, meaning that the persistent objector rule cannot apply. Such norms are not based on the consent or conduct of any State, or even a particular group of States, but are instead rooted in a recognised legal conviction of the international community as a whole. They possess a collective foundation that cannot be traced to the practice or agreement of any particular State. International GPLs emerge through a broad and decentralised process of recognition across the international community. Their legal authority is, therefore, diffuse in the sense that it is dispersed throughout the legal order rather than concentrated in the express consent of individual States. For this reason, the persistent objector rule is inapplicable to international GPLs.
3.3.2. No derogation from fundamental principles?
A second argument that may be advanced is that there are statements made by States asserting that the persistent objector rule cannot apply to fundamental principles of law or general principles of international law—that is, GPLs formed within the international legal system. For instance, in 2016 Greece stated in the UN Sixth Committee (Legal), when discussing custom, that its delegation doubted the applicability of the persistent objector rule not only to jus cogens ‘but also to the broader category of the general principles of international law whose applicability did not seem to depend on States’ consent’.Footnote 119 Elaborating further on the non-applicability of the persistent objector rule to internationally-derived GPLs in 2018, the delegation stated:
The specific character of those general principles justified their exclusion from the scope of application of the persistent objector rule, as it would indeed be odd to argue that a State would not be bound by rules having a fundamental character for the international community; there appeared to be no evidence of such an extended application of that rule even in the decisions of international courts. It was hard to imagine how a State could qualify as a persistent objector to such uncontested general principles of international law as the right of innocent passage, the objective legal personality of international organizations or the principle of sustainable development, even if those rules did not qualify as jus cogens.Footnote 120
This position has also been endorsed by other States in the UN Sixth Committee (Legal). For instance, in 2016 Cyprus, referring to the ILC topic on custom, argued that the persistent objector rule would be inapplicable to ‘other types of rules of fundamental importance’,Footnote 121 which could be read to mean internationally-derived GPLs.
These statements by States that the persistent objector rule does not apply to fundamental principles of law also find support in judicial pleadings before the ICJ. For example, the UK’s pleadings in the Anglo-Norwegian Fisheries case took the position that the persistent objector rule cannot apply ‘where a fundamental principle is concerned’, adding that ‘the international community does not recognize the right of any state to isolate itself from the impact of the principle’Footnote 122 (in that case, the principle of the freedom of the high seasFootnote 123 and the right to coastal watersFootnote 124). Certain international GPLs may indeed have this fundamental character—for instance, the principle of State consent referred to by Akande—such that no objection could be made against them. Yet, it must be noted that the ICJ in its judgment referred to the norm to which Norway was found to have persistently objected as ‘general international law’, a term that encompasses both customary international law and GPLs.Footnote 125 Importantly, the ICJ was not specifically addressing GPLs as distinct from customary international law. Rather, on the merits the Court was not terminologically precise in its discussion of the persistent objector rule, referring broadly to ‘general international law’ in a way that could potentially include both custom and GPLs.
As such, the above shows that there is State practice and conduct, indicating that the persistent objector rule does not apply to fundamental GPLs. State practice is here being shown not to establish custom, but rather as evidence of how States understand the nature of a GPL obligation and the non-applicability of the persistent objector rule. The relevance of practice is thus interpretative and classificatory rather than constitutive.
3.3.3. The persistent objector rule would undermine the international legal system as a whole
The third argument for why the persistent objector rule cannot apply to GPLs formed within the international legal system is that its application would undermine the international legal system itself. Under Draft Conclusion 10(2) of the ILC’s draft conclusions on GPLs, such principles ‘may be resorted to when other rules of international law do not address or resolve a particular issue in whole or in part’.Footnote 126 Their principal function is therefore to fill gaps in the law and to ensure the coherence and completeness of the international legal system. If States were permitted to invoke the persistent objector rule to exclude the application of such a principle as it is being developed, this gap-filling function would be compromised. Rather than resolving lacunae, the rule would create new gaps and increase the likelihood of non liquet. Such a result would run directly counter to the intentions of the PCIJ Advisory Committee of Jurists, which sought to ensure that international adjudicators would not be left without applicable law.Footnote 127 More broadly, it would undermine fundamental structural features of public international law and frustrate one of the core purposes of GPLs.
A hypothetical example illustrates the point. The general principle of the freedom of the high seas has, over time, been qualified and supplemented by a range of environmental principles designed to reconcile competing interests and to address gaps in the law. These principles help to ensure that the high seas are used consistently with contemporary environmental obligations and concerns. One example is the principle of common heritage of humankind as it applies to the deep seabed, which fills an important gap in the regulation of the oceans.
To illustrate the point further, even if one were to assume hypothetically that the US objectedFootnote 128 to the principle of common heritage of humankind which formed within the international legal system itself,Footnote 129 this would not affect the validity of the principle as a GPL, since it only needs to meet the minimum threshold of being recognised unanimously or near-unanimously by the international community.Footnote 130 As Willaert notes, the US has not been persistent enough for the rule to apply in any case.Footnote 131 More importantly, near-universality itself suffices, implicitly accommodating States that do not share the principle or fail to recognise it. This goes back to the previous point on the nature of GPLs as they transcend the will of individual States.
Allowing States to opt out of such principles through persistent objection would weaken the legal framework governing the high seas and impair the coherence and completeness of the international legal system. Had the ILC endorsed such an approach, it would have risked serious damage to the international legal system by undermining its fundamental principles and, more generally, the literature on legal systems.Footnote 132
This view finds some support in the Written Comments of Belarus on the identification of customary international law, emphasised that the persistent objector rule should not harm the ‘international community [or] the integrity of the international legal system as a whole’.Footnote 133 This reinforces the idea that applying the persistent objector rule to international GPLs could undermine the consistency and coherence of international law, effectively allowing States to create their own patchwork of ‘international law’ and thereby weakening the rule of law.
For these reasons, permitting the persistent objector rule to apply to GPLs formed within the international legal system would be contrary both to the nature of GPLs and the concept of an international legal system as such.
3.3.4. The Climate Change AO as a recent example of an arguable invocation of the persistent objector rule
As noted in Section 3.3.3, the US also objected in its Written Comments in the Climate Change AO to the precautionary and the CBDR principles, arguing that neither constitutes customary law nor a GPL.Footnote 134 This represents one of the most recent examples where the persistent objector rule was raised in pleadings. Each principle will be discussed in turn.
The US opined in its Written Comments in the Climate Change AO that the precautionary principle is not a GPL,Footnote 135 reiterating its long-standing position from the World Trade Organization (WTO) case EC–Measures Affecting the Approval and Marketing of Biotech Products,Footnote 136 where the panel declined to engage with it as ‘unsettled’ law.Footnote 137 The US argued that the principle’s content varies from treaty to treaty,Footnote 138 and lacks a clear, generally accepted function, preventing recognition by States.Footnote 139 The ICJ’s position, as expressed in its Climate Change AO, is somewhat opaque: it consistently refers to a ‘precautionary approach or principle’, notes its inclusion in the UN Framework Convention on Climate Change (UNFCCC) and describes it as a guiding principle for interpreting climate change treaties,Footnote 140 functions comparable to those identified in Draft Conclusion 10 of the ILC’s work on GPLs. The issue with the precautionary principle is that, given the widespread disagreement among States regarding its normative character, it cannot be said to reflect universal recognition sufficient to affirm its status as a GPL. This is evident in the ICJ’s indeterminate position on whether precaution constitutes a principle or merely an approach. Therefore, it can be argued that it does not yet qualify as a GPL, notwithstanding its inclusion alongside other GPLs in the Climate Change AO.Footnote 141
A similar objection was raised against CBDR,Footnote 142 another international GPL, with the US asserting that ‘there is no generally accepted formulation of CBDR, much less a generally shared understanding of what it means’.Footnote 143 It pointed to variations between Principle 7 of the Rio Declaration (‘states have common but differentiated responsibilities’),Footnote 144 Article 3(1) UNFCCC (CBDR with ‘respective capabilities’ (CBDR-RC)),Footnote 145 and Article 2(2) of the Paris Agreement (‘CBDR-RC … in light of different national circumstances’).Footnote 146 From this, the US concluded that the Rio Declaration states ‘political’ rather than legal principles. Yet, such variations may simply reflect the principle’s evolution. Its core—that all States share common responsibilities, but their implementation is differentiated by national capabilities—has been widely acknowledged.Footnote 147 Being abstract, principles are capable of evolutive interpretation and function.
Strikingly, the US explicitly declared at Rio, and has continued to reiterate, that it ‘does not accept any interpretation of Principle 7 that would imply a recognition or acceptance by the United States of any international obligations or liabilities, or any diminution in the responsibilities of developing countries’.Footnote 148 However, this concerns interpretation rather than recognition of the principle itself.Footnote 149 Indeed, the US-China Joint Glasgow Declaration on Enhancing Climate Action in the 2020sFootnote 150 emphasised the CBDR principle in enhancing climate action as it constitutes the foundation of the international climate change regime. Impliedly, this shows US recognition of the CBDR principle. The objection, therefore, targets historical responsibilities rather than CBDR as such.Footnote 151 In any case, it cannot amount to a persistent objection: the US has not consistently opposed the principle despite using the language of ‘opposition’.Footnote 152
By contrast, the ICJ affirmed that CDBR is a ‘core guiding principle for the implementation of the climate change treaties’Footnote 153 encompassing historical responsibilities and, therefore, cannot be excluded by unilateral objection.Footnote 154 Arguably, the language of the Court reflects that the CBDR is a fundamental or even intrinsic principle to the climate change regime and, therefore, cannot be objected to.Footnote 155 The Court stated that CBDR is a ‘manifestation of the principle of equity’.Footnote 156 The Court’s approach demonstrates that these principles reflect a common understanding at the international level.
Besides these two recent examples, as Bjorge highlighted in a previous article in this journal, the principle of res judicata is a general principle formed within the international legal system.Footnote 157 As a structural principle necessary for the functioning of international courts and tribunals, it would be illogical to accept the possibility that such objection could be made, as this would undermine legal certainty—a fundamental feature of adjudication. On a related point, Đorđeska points out that even if a State objects to an emerging customary norm, that State may still be bound by the same norm if it also exists as a GPL, because international GPLs are intrinsic to the international legal system.Footnote 158 Though this may be unlikely, it is conceptually possible. As the main criterion, Draft Conclusion 7 of the ILC work on GPLs, adopted at second reading, provides that the identification of international GPLs requires recognition by ‘the community of nations’ that the principle is intrinsic to the international legal system.Footnote 159 This phrasing suggests the need for a plurality that excludes the possibility of individualistic objections. The main point is that GPLs emerge from the community of nations as a whole, as demonstrated by near-universal recognition, meaning that consent is not needed from States. Thus, GPLs do not allow for opt-outs in the same way as custom. Even the argument that GPLs formed within the international legal system itself are similar in nature to rules and principles of customary international law, and that the same position should, therefore, apply to them, fails to take into account the four points discussed in this section.
To conclude, this section has shown that the persistent objector rule cannot apply to GPLs formed within the international legal system. Four reasons have been given to justify this conclusion. First, there is an arguably similar character between GPLs and jus cogens, in that both have a communitarian nature. Second, and relatedly, there can be no derogation from fundamental principles, a point supported by State practice and pleadings before the ICJ. Third, the application of the persistent objector rule would undermine the international legal system as a whole. Finally, the section has analysed the pleadings of the US in the Climate Change AO, which may be seen as an outlier; however, the ICJ did not engage with these arguments. Taken together, these four arguments against the applicability of the rule are reinforced by the current wording of Draft Conclusion 7 on GPLs, under which the identification of international GPLs must be intrinsic to the international legal system, making the application of the persistent objector rule conceptually inconceivable.
3.4. The persistent objector rule and regional or subregional GPLs
With the ILC’s introduction of Draft Conclusion 12, which recognises GPLs with a limited scope of application ratione personae, namely principles applicable at the regional, subregional, bilateral or other non-universal levels (excluding subject-specific GPLs such as those relating to international criminal law or international environmental law), the question arises whether the persistent objector rule may apply to such principles. The two preceding case studies have shown that the persistent objector rule is incompatible with universal GPLs.
From the outset, bilateral GPLs are excluded from this analysis. These principles are typically identified by comparing the legal systems of the two States involved in a dispute, either pursuant to the applicable law or after all relevant legal rules have been exhausted.
For the purposes of this article, the term ‘regional GPLs’ encompasses both regional and subregional GPLs. To date, this issue of regional GPLs and the persistent objector rule has not been addressed in literature. It is argued that, in the context of regional GPLs, the crucial issue arising when a State objects to their application is not whether the principle itself is invalid or objectionable. Rather, the issue is whether it is appropriate to refer to a legal principle originating in another legal system. Accordingly, such objections are qualitatively different from the type of objection contemplated by the persistent objector doctrine properly so-called.
As this author has argued elsewhere, there is a distinction between the origins or extrapolation processes of regional GPLs.Footnote 160 Broadly, three pathways can be identified, and the analysis in this section will be divided along the same lines: (i) extrapolation from domestic legal systems of Member States; (ii) extrapolation from international law; and (iii) development within the regional system itself.
3.4.1. GPLs extrapolated from domestic and international legal systems
Similarly to domestic and internationally-derived GPLs, regional courts use a ‘majority approach’ to establish the existence of a GPL, a process that does not permit individual Member States to raise objections.Footnote 161 In relation to general principles of EU law, Akehurst has argued that regional GPLs extrapolated from domestic legal systems do not require recognition by all Member States in order to be recognised and applied by the Court of Justice of the EU.Footnote 162 Instead, it is sufficient that a large majority of States adopt or recognise the principle, with this so-called majority approach justifying recognition as a general principle of EU law.Footnote 163 Even those States that remain silent or are in the minority are bound by such principles.Footnote 164
This position has support in scholarship, with several commentators pointing out that Article 38(1)(c) ICJ Statute does not require recognition by all States but only that the principle should be found in most legal systems.Footnote 165 By analogy, this majority approach can also apply to GPLs extrapolated at the international level, whether from domestic legal systems or from international law.Footnote 166 Thus, the same logic may be extended to situations in which a regional legal system adopts principles borrowed from the international legal system. Since these principles are already universally or near-universally recognised, the persistent objector rule has no application within the regional legal system.
3.4.2. GPLs originating from a regional legal system
Thus far, this article has argued that the persistent objector rule is not applicable in relation to GPLs. However, this assertion may need to be qualified in relation to principles which emerge within a regional legal system (for instance, the EU), insofar as these principles possess a special character confined to that particular regime. Problems could arise if such principles are invoked in other regional or international settings, without bearing in mind their specific limited scope of application. For instance, if the East African Court of Justice attempted to apply a principle unique to EU law, a party could object on the basis that it is culturally and legally inappropriate to transplant a principle from one regional order into another. This hypothetical scenario, however, does not concern the application of the persistent objector rule stricto sensu but, rather, objections that arise in relation to the appropriateness of transposing legal principles from one regional legal system to another.
The main question is thus whether a GPL that exists in one regional legal order can exist in another legal order (either as a general principle of international law or as a particular general principle of that regional order). This point was discussed by Paparinskis at the seventy-sixth session of the ILC, where he referred to ISDS cases in which the US objected to the application of the principle of proportionality on the basis that it originated in European legal traditions and thus had only a limited scope of application.Footnote 167
The principle of proportionality, developed in Germany and France and later incorporated into EU law, is considered a cornerstone of European legal reasoning.Footnote 168 It has also been applied by the European Court of Human Rights,Footnote 169 various national courtsFootnote 170 and in other regimes such as the law of armed conflict,Footnote 171 WTO lawFootnote 172 and in ICJ jurisprudence.Footnote 173 While the US has objected to its application in ISDS cases, this objection does not seem to challenge the existence of proportionality as a principle but, rather, its scope and the way tribunals have expanded obligations on States within the ISDS regime.Footnote 174 Indeed, even US domestic law exhibits traces of proportionality reasoning, thereby weakening the claim that the US has persistently rejected the principle outright or that its statements in ISDS proceedings definitely exclude it, as suggested by Paparinskis.Footnote 175
Critiques of the case relied upon by Paparinskis, Occidental v Ecuador (II), do not mention that the US invoked the persistent objector rule. Rather, they criticise the tribunal for imposing proportionality-based obligations on States despite the absence of any explicit reference to such obligations in the underlying bilateral investment treaties.Footnote 176 This shifts the focus to a comparative inquiry concerning the appropriateness of relying on external legal sources, rather than to a claim of persistent objection. As discussed in Section 1, the persistent objector rule operates in the context of emerging norms, not once a rule has already crystallised. This is distinction was critical in Occidental v Ecuador (II): the issue was not the emergence of new GPL, but whether proportionality, often characterised as a predominantly European principle, could appropriately be applied in the ISDS context. Similarly, in Denis Yevdokimov and Artiom Rezanov v Russian Federation, two European members of the UN Human Rights Committee (Thelin and O’Flaherty) rejected reliance on the proportionality principle under the European Convention on Human Rights, not because they denied its existence, but because they deemed it inappropriate in that specific human rights context.Footnote 177 These cases illustrate the distinction between objection to an existing norm and objecting to the development of a norm, which the persistent objector doctrine is designed to address.
In sum, it can be clearly stated that the persistent objector rule is not applicable to regional GPLs when they are invoked in other regional legal orders and a State objects to their application or a court ultimately rejects that objection. Moreover, there is no evidence that regional GPLs have been rejected wholesale by another regional legal order. At most, regional or specialised judicial bodies may decline to apply a principle originating in another system on grounds of incompatibility or interpret their own regional principles as lex specialis, prevailing over those from elsewhere. This suggests that the issue is better understood as one of the reception of external regional principles, rather than one of persistent objection. Accordingly, there is neither judicial nor State practice to support the claim advanced by Paparinskis in Section 2.2 that the US objected to the principle of proportionality in a manner capable of establishing the applicability of the persistent objector rule to GPLs, including regional GPLs. At best, this argument is indirect. The available examples demonstrate judicial sensitivity to the regional origins of certain principles, but they fall well short of establishing the kind of clear, formal and consistent objection required by the persistent objector doctrine. For the time being, the more persuasive view is that the persistent objector rule remains inapplicable to GPLs, whether universal or regional.
3.5. General observations
Beyond the conceptual and theoretical analysis, some general observations can be made about whether the persistent objector rule has any practical utility when applied to GPLs. Using Green’s analytical framework on the practical utility of the persistent objector rule, four points can be identified:Footnote 178 (i) the theoretical misconceptions of GPLs; (ii) the limited practical utility of the persistent objector rule against GPLs; (iii) the inability of the persistent objector rule to influence the development of GPLs; and (iv) the lack of compelling evidence supporting the application of the rule to GPLs.
3.5.1. Theoretical misconceptions of GPLs
It may be observed that there are several theoretical misconceptions: first, that GPLs are fully voluntaristic; second, that there is no communitarian element; and third, that GPLs can be subject to consent. As Green’s influential work on the persistent objector rule shows, the rule is applicable to custom and is grounded in the predominant justification of preserving a voluntarist approach to international law.Footnote 179 In other words, the persistent objector rule functions to affirm voluntarism in customary international law (although some may also argue that custom is not voluntaristic). This already suggests that the persistent objector rule is inapplicable to GPLs, whose theoretical foundation is different. GPLs are not rooted exclusively in voluntarism but in a blend of natural law and positive law.Footnote 180 It must be acknowledged that there has long been disagreement over whether GPLs are positive or natural, but the majority of scholarship appears to agree that they are hybrid creatures, reflecting a mixture of positive and natural law.Footnote 181 This proposition is supported by the Judge Tanaka, who argued that the drafting of Article 38(1)(c) ICJ Statute represents a harmonisation between common law proponents of positive law and civil law proponents of natural law, i.e. the ‘compromise between the two schools’.Footnote 182
The misconception of GPLs as a voluntaristic source of law, linking them to State consent and thereby creating a form of ‘custom-lite’, though long-standing, has been reignited by past ILC members.Footnote 183 Although the distinction between GPLs and custom has a longer historical pedigree, as Cheng has observed, the demarcation line between them ‘is not often very clear’.Footnote 184 Owing to this conceptual uncertainty surrounding GPLs, some scholars, such as Pellet, have argued that custom and GPLs are not fundamentally distinct, suggesting that both sources ‘provide general guidelines which then have to be applied by the Court in the particular case’.Footnote 185 On this view, both operate as frameworks, functioning in a structurally similar manner as abstract guidelines rather than as detailed rulebooks. While this assertion that they are not fundamentally distinct may hold true in terms of legal practice, there remains a plausible theoretical argument for maintaining a fine-grained distinction between these two sources of law. Thus, the misconception that GPLs are voluntaristic in nature has been rebutted, as they occupy a middle ground between positive and natural law.
Second, there is a misconception that GPLs do not have a communitarian nature. This misconception stems from an unduly restrictive reading of Article 38(1)(c) ICJ Statute, which treats general principles merely as interpretative tools or material sources of international law.Footnote 186 This misconception of GPLs is not accurate, because it overlooks the role of the interests of the international community in their formation and because recognition of GPLs requires recognition by the ‘community of nations’ as stated in Draft Conclusion 2. Voigt argues that GPLs (whether derived from domestic systems or internationally) should be treated as emerging from the opinio juris communis of the international legal order,Footnote 187 thus embodying the reality of the communitarian nature of GPLs. In custom, the persistent objector rule is premised on its use as a bargaining tool by individual States during the formation of custom; this logic is not transferable to GPLs. As such, the communitarian school of thought weakens the case for the persistent objector rule. For communitarians, GPLs express the shared legal reasoning of the international community, not bargains between individual States.Footnote 188 Thus, it rebuts the premise that GPLs are not communitarian.
The third and final misconception is that GPLs cannot be explicitly ‘recognised’ or ‘consented to’ by States in the same way treaties can.Footnote 189 Although custom cannot be either, there is a sense of ‘implied consent’.Footnote 190 Their nature makes such explicit expressions of consent impossible. As Greig observed, even in the limited instances where the ICJ has applied GPLs, the Court never examined whether States had ‘recognised’ them, nor did it look for a consent requirement.Footnote 191
Given that the purpose of the persistent objector rule according to Green is to preserve voluntarism, the lack of the need for consent in the formation of GPLs renders it redundant in relation to them.Footnote 192 GPLs are designed to reflect the commonality of legal reasoning across States, not the will of individual States. They function as fundamental tools of legal reasoning, infused with elements of natural law,Footnote 193 with some but not all of them possessing inherent moral values similar to jus cogens norms.Footnote 194 States do not have full control over them as their formation transcends State consent. This extra-consensual nature rests on the ‘good and the just’.Footnote 195 This is particularly evident in dispute settlement, where principles such as pacta sunt servanda operate independently of States’ immediate will.Footnote 196 This is partly because principles, unlike rules, are merely recognised, whereas in custom opinio juris denotes a legal conviction that they are bound by that rule, so there is already an internal thinking about a legal duty.Footnote 197 According to Draft Conclusion 2, recognition must be by the community of nations ascertained in an objective fashion, taking into account all the available evidence.Footnote 198
In sum, these three misconceptions have been rebutted: first, GPLs are not purely voluntaristic.Footnote 199 Hence, GPLs should not be reduced to ‘custom-lite’,Footnote 200 as this would blur the distinction between custom and GPLs. Second, they reflect what the community of nations recognises as GPLs, leaving no room for unilateral carve-outs by powerful States. Third, they cannot be expressly consented to in the same way as treaties. Thus, it can be stated that Green’s justification for the persistent objector rule is not relevant to GPLs because it rests on a theoretical misconception about their nature as voluntaristic sources of law.
3.5.2. Limited practical utility of the persistent objector rule in relation to GPLs
Green highlighted the practical role of the persistent objector rule as a ‘safety valve’ mitigating the risk of non-compliance with custom by allowing States to opt out of rules which they have persistently opposed.Footnote 201 This logic does not apply to GPLs, further demonstrating the rule’s incompatibility with GPLs. Three reasons are offered.
First, the threshold for recognising GPLs is arguably higher than for custom: GPLs must be recognised universally or near-universally. Whereas a rule of custom can be created by the practice of a single State, as the ICJ noted in relation to Norway in the Anglo-Norwegian Fisheries case, this is only the case as long as it has been accepted as such by the majority of other States and the conditions for the persistent objector rule have been fulfilled. GPLs are by their nature communitarian rather than dependant on the approach of individual States. However, the same may also be said of custom, as individual States cannot simply veto the formation of customary international law, though they can prevent it from becoming binding on them via the persistent objector rule.
Second, the cost-benefit analysisFootnote 202 of objecting to abstract principles yields an unfavourable result. GPLs are often codified in treaties’ texts or their preambles, resolutions, declarations, soft-law instruments, expressed in judicial reasoning or underpin other legal rules such as custom or fields of international law, such as international environmental, humanitarian or human rights law, but conceptually they are not ‘rules’ in the strict sense.Footnote 203 The main point is that the character of a GPL is more abstract and general than other sources of law.Footnote 204 Objecting to such abstract principles may be costlier and less effective than objecting to precise customary norms, where there is the possibility for a short-term adjustment rather than a need to rebut the rule as a whole. The cost is higher for States because, for example, with respect to a principle in foro domestico, they would need to monitor the development of principles across numerous domestic legal systems and begin objecting to them. It is difficult to imagine that any State would have the capacity to undertake such a task.Footnote 205 Also, it would be a breach of the prohibition to intervene in the domestic affairs of another State under Article 2(7) of the UN Charter.Footnote 206 The same applies to international GPLs: States would become extremely cautious about using the terms ‘GPL’ or ‘principle’. The costliness argument may be supported from a judicial perspective by the fact that, although there is no hierarchy between sources of law,Footnote 207 the ordinary method of international courts and tribunals is to only resort to GPLs after treaties or custom.Footnote 208 It therefore appears to be of limited benefit for a State to object to an abstract principle, which, due to its general character, is more flexible and open to interpretation from the start.
Returning to the point that GPLs are not strictly ‘rules’, it is not suggested that GPLs are not ‘binding’ sources of law, they certainly are. However, some scholars have attempted to reduce them to mere interpretative or material sources of international law.Footnote 209 If this view were adopted it could be argued that the persistent objector rule does not apply because GPLs are not ‘hard’, binding law. This would be a dangerous approach, as it would render all established GPLs non-binding, such as the principle of equality of States, res judicata or the principle that municipal law should not prevail over international law. A further argument that GPLs may be non-binding is rebutted by the clear doctrinal analysis of Saunders, who demonstrates that the ICJ uses GPLs as a binding source of law,Footnote 210 and scholarship more broadly agrees that GPLs constitute a formal source of law.Footnote 211 Draft Conclusion 10(1)(a) likewise confirms that GPLs may serve as a basis for substantive obligations, have substantive effect and contribute to the coherence of international law.Footnote 212
Third, the safety valve function is irrelevant for GPLs.Footnote 213 Similarly to custom, breaches of GPLs may entail State responsibility,Footnote 214 but unlike custom, non-compliance cannot be excused by persistent objection rendering a particular rule non-binding on a State. Nor is there any need for short-term adjustment periods,Footnote 215 as GPLs are inherently abstract, flexible and fluid,Footnote 216 capable of gradual evolution through adjudication.Footnote 217 In contrast, custom is often detailed and precise and may, therefore, require transitional opt-outs.
In sum, the persistent objector rule’s main practical functions—protecting voluntarism, reducing non-compliance and facilitating adjustment—do not translate to GPLs.
3.5.3. The persistent objector rule and the development of GPLs
Finally, Green argued that the persistent objector rule can sometimes act as a ‘lobbying or negotiation tool’ in the formation of custom, nudging rules to develop in different directions.Footnote 218 Could the same by said of GPLs? The answer is no. GPLs, given their abstract and systemic nature, do not require such modification. Their flexibility allows them to be shaped and applied through adjudication without the need for State objections. Moreover, the dialectic processFootnote 219 underpinning the persistent objector rule in custom, where objectors signal their dissent and others respond, has no equivalent in GPLs. States may object to a principle being applied in a given dispute, but this does not constitute persistent objection in the context of its formation.Footnote 220 GPLs reflect shared legal foundations (such as pacta sunt servanda), not iterative bargaining processes among States.
3.5.4. Limited evidence of the rule’s application to GPLs
The final, and by far the most compelling argument against the applicability of the persistent objector rule to GPLs is that no international court or tribunal has endorsed such a possibility. As this article has shown, certain members of the ILC and some States have expressed the view that the rule should apply to GPLs (see Sections 2.2 and 2.3). However, the relevant State practice and scholarship remain limited, and there is no evidence of any sustained attempt to invoke the rule in this context, with the recent US example being the only possible exception. This silence is significant. In fact, it should be emphasised more strongly, as it offers a powerful response, especially for positivists, to the intuitive default to voluntarism that many might adopt in approaching this question.
3.5.5. Conclusions
In sum, from a practical perspective, three misconceptions have been rebutted, demonstrating that the persistent objector rule offers no utility: it cannot serve as a safety valve, a short-term modification tool or a mechanism for shaping the development of principles, and this is reflected in the very limited support for the rule’s application to GPLs.
4. Conclusion
The article answers a question that was not addressed by the ILC at its seventy-sixth session, namely whether the persistent objector rule is applicable in relation to GPLs. This issue has previously not been addressed in legal scholarship, with only one or two scholars noting it in passing. The article has, therefore, sought to close this gap. At the outset, it demonstrates that the persistent objector rule is historically not confined to customary international law, but could prima facie apply across different sources of international law during their formation processes.
The article first sought to explore what GPLs are, noting their status as the third source of international law, as reflected in Article 38(1)(c) ICJ Statute. Two main categories of GPLs and a third, newly-conceived one were identified: (i) GPLs derived from domestic legal systems; (ii) those formed within the international legal system; and (iii) regional GPLs. These three categories were used as case studies in Sections 3.2 to 3.4. Having defined GPLs, the article then provided a brief chronological overview of how the persistent objector rule entered the ILC’s discussions on GPLs, including the US proposal, and categorised the views of ILC members, noting a divided Commission.
Section 3.1 highlighted the conceptual and theoretical nature of GPLs, in particular that consent has little to do with them. GPLs occupy a position at the intersection of positive and natural law. Because of this hybrid nature, they are difficult to reconcile with the persistent objector rule, which is designed to safeguard sources of international law (custom) grounded in a stronger voluntarist conception of State consent.
In the first case study on domestically-derived GPLs, two scenarios were examined in terms of the level of State recognition required. If only some States recognise a principle while others do not, there is arguably no sufficiently widespread recognition, and a GPL cannot be formed. However, where only a few States remain silent, a GPL may still be formed. This highlights that there is nothing to which a State can meaningfully object if it does not yet know whether a principle will crystallise as a GPL. Requiring States to monitor every legal system and object to principles as they emerge in other jurisdictions would be both impractical and unduly burdensome. Even the recent argument made by the US in the Climate Change AO in relation to the polluter-pays principle did not fail on recognition, but on the appropriateness of transposition into international law. The principle was already established, not still in development.
In the second case study on GPLs formed within the international legal system, four main arguments were advanced as to why the persistent objector does not apply. First, GPLs share a communitarian nature similar to jus cogens and are more homogenous in character than custom. Second, State practice indicates that derogation from fundamental principles which define the international legal system is not permissible. Third, and relatedly, allowing the persistent objector rule to operate in relation to international GPLs would undermine the international legal system as a whole, creating a patchwork of fragmented regimes, and would contradict one of the main functions of GPLs, namely, gap-filling where treaties and custom are inapplicable. If international courts and tribunals were unable to apply certain GPLs because a State in the dispute had persistently objected, this would generate multiple lacunae in the law, leaving courts and tribunals without any way to address them. Finally, the article examined the invocation of the persistent objector rule by the US in the Climate Change AO in relation to the precautionary and CBDR principles, with which the ICJ did not engage.
The third case study examined whether the persistent objector rule applies to regional GPLs, a category introduced into the ILC Draft Conclusions at its seventy-sixth session. It also addressed Paparinskis’ suggestion regarding whether regional GPLs, once applied in another regional legal system, could be objected to. The analysis first explained how regional GPLs emerge, showing that they may originate from Member States, international law or the regional legal system itself. However, the question of whether a regional GPL can be objected to when applied in another regional system does not concern the persistent objector rule. Rather, it concerns the appropriateness of applying a norm in a different legal system. It therefore falls outside the scope of the persistent objector doctrine.
In the final part of the article, four general observations were made. First, GPLs are not fully voluntaristic; they are communitarian in nature, and consent plays only a limited role. Second, there is little practical utility of applying the persistent objector rule in relation to GPLs. It is difficult to see why a State would object to an abstract principle, whether domestically derived or internationally formed. From a practical perspective, this would be especially burdensome for small or developing States, whose foreign ministries may lack the capacity to monitor whether domestic principles in other States may evolve into GPLs. Third, the purpose of the persistent objector rule as a tool for influencing the development of emerging customary norms does not translate well to GPLs, which are more abstract and context-dependent. Fourth and finally, although there has been some academic and ILC discussion on the relationship, no international court or tribunal has endorsed the applicability of the rule to GPLs.
Taken together, these arguments show that the persistent objector rule has no role to play in relation to GPLs. From a realist perspective, the implications of this article may attract criticism from positivist legal scholars who are reluctant to dilute the role of custom. For States, it is likely that they would argue that States should retain the full ability to withhold consent from emerging legal principles. Moreover, the article may serve as a wake-up call, making States aware that they should be cautious when referring to GPLs, and potentially leading to the more explicit formulation that they ‘object to it as both custom and a GPL’. Hence, stronger strategic contestation of legal principles may be required. The effect may be the reduced acceptance of GPLs as a source of international law, especially in relation to the second category of internationally-derived GPLs, if States can be bound with no way to opt out. Judicially, States may have heightened concerns about judicial activism where GPLs are employed. Essentially, without the impression that there is a method for avoiding being bound unwittingly in the form of the persistent objector rule (even though that rule in fact cannot play a role in the formation of GPLs), States may perceive GPLs as an overly autonomous source of international law and may respond by resisting, narrowing or disregarded their application. Whether this will materialise remains to be seen.
Acknowledgements
The author serves as Assistant to the ILC Special Rapporteur on General Principles of Law, HE Ambassador Marcelo Vázquez-Bermúdez. All views expressed are the author’s own. Special thanks to Professor James Green, Professor Mads Andenas KC and Professor Harro van Asselt for their valuable feedback on earlier drafts. The author would also like to thank Anna Riddell-Roberts for her feedback. All remaining errors are the author’s own.
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