Chapter 4 The Legal Effect of Domestic Rulings in International Law

In: Domestic Courts and the Interpretation of International Law
Author: Odile Ammann
Open Access

In this chapter, I examine the legal effect of domestic rulings in international law. I argue that this effect has both static and dynamic elements. On the one hand, and this is what I refer to as the static effect, domestic courts enable States to respect their international obligations. On the other hand, from the angle of the sources of international law, domestic judicial decisions also have what I call a dynamic effect on international law. First, and as becomes apparent when analyzing art. 38(1)(a)–(c) of the Statute of the International Court of Justice (icj), domestic rulings can collectively contribute to the formation and modification of international law. Second, from the vantage point of any domestic or international interpreter of international law, domestic judicial decisions are what I refer to as auxiliary means (or ‘subsidiary means’, pursuant to art. 38(1)(d) icj Statute) that assist her in her interpretative task.

Theories which emphasize the incompleteness of the law usually argue that courts have a dual function: to apply law and to create new or revise old law. The prevalence of interpretation, however, seems to belie this view. Interpretation straddles the divide between the identification of existing law and the creation of a new one.816

1 Introduction

In this chapter, I examine the legal effect of domestic rulings in international law. I argue that this effect is both static and dynamic.817 First, domestic courts enable States to respect their international obligations. They do so by enforcing international law domestically (infra, section 2). Second, from the perspective of the sources of international law, domestic judicial decisions also have a dynamic effect on international law, as they contribute to shaping it, on the one hand, and help interpreters ascertain it, on the other hand (infra, section 3).818 I explain my reasons for focusing on art. 38 icj Statute in Chapter 2, section 5 (supra).

Why highlight the legal effect of domestic rulings in international law? Simply put, because a normative argument about how domestic courts must interpret international law requires understanding the essence and characteristics of their activity, and its relevance and stakes. Joseph Raz has observed that answering the question of how interpretation must be conducted (with regard to both legal acts and other interpretative objects) must start with an account of what interpretation is, and of why it is necessary and important (supra, Introduction, section 2).

Part 1 of this book revolved around the question ‘What is interpretation?’, and more precisely around the question: what is the nature and essence of domestic (especially Swiss) courts’ interpretation of international law? To answer this question, I have defined the scope of my inquiry (Chapter 1), laid its conceptual groundwork (Chapter 2), and provided context on the Swiss legal order (Chapter 3).

In Part 2, my goal is to address Joseph Raz’s second question – why interpret? In other terms, why is legal (and, more specifically, judicial) interpretation ‘central to legal practices’?819 As Raquel Barradas de Freitas notes, the word ‘central’ can designate the predominance of legal interpretation in legal practice, but also (and more convincingly) its instrumental role (ie, ‘its relevance to the pursuit of a series of ends’).820 The ‘why’ question is distinct from, and prior to, the question of how to interpret.821

While I adopt Raz’s three-pronged structure of inquiry, my endeavor differs from his legal philosophical analysis of interpretation (supra, Introduction, section 2), and from his approach to the ‘why’ question. Instead of taking the perspective of an observer of the practice, as Raz does, I answer the ‘why’ question by analyzing the law as a participant in the practice. Unlike Raz, who looks at domestic law, my focus lies on international law.

As much of international legal scholarship confirms,822 it is tempting to understand Raz’s ‘why’ question as one that is about the ‘role’ of domestic courts when they interpret international law.823 The term ‘role’, however, is multifaceted and ambiguous. A role can be captured from a descriptive or from a normative angle.824 It can be analyzed through the lens of domestic or international law. It can be defined from a legal perspective (ie, by highlighting courts’ or States’ legal duties and authority), but also from a psychological or sociological perspective, etc. This role may differ depending on the source, norm, and substantive area of international law under scrutiny.825 Accordingly, scholarship addressing the ‘role’ of domestic courts in the interpretation of international legal acts is a thicket that is hard to penetrate.826

A closely related point, and a distinctive feature of recent scholarly analyses, is that many authors adopt functionalist approaches. This should not surprise us in light of the aforementioned comments, since functionalism is an epistemic method that focuses on the role (or purpose) a given object serves – this role is deemed to have explanatory value. To illustrate, scholars have enumerated domestic courts’ modes of ‘engagement’827 with international law, or the range of ‘functions’ these courts fulfill when interpreting it.828 Functionalist approaches have often been used by international lawyers,829 eg with regard to international courts,830 and they have also been popular in domestic law.831

At first sight, functionalism is attractive because it allows us to draw a range of distinctions and to think analytically. Yet one important drawback of functionalism is its indeterminacy. How should we select among the myriad ‘functions’ courts perform? Why is one function deemed more important than others? Functionalism invites disagreement, as different functions are likely to be emphasized depending on the set of beliefs the scholar endorses. While purporting to be descriptive and analytically precise, functionalism substantially hinges on more fundamental value judgments.832

Rather than examining the ‘functions’ or causal ‘impact’ of domestic judicial decisions in international law, my aim, in this chapter, is to clarify why domestic courts’ interpretations of international law are central (ie, important, instrumentally relevant) to the practice of international law. In other terms, I examine the legal effect of these rulings in international law.

As usual, caveats apply. First, the two aforementioned aspects (ie, the law-applying, ‘static’ facet of domestic courts’ activity, versus its jurisgenerative, ‘dynamic’ effect)833 are two sides of the same coin.834 By enforcing international law domestically as international law requires States to do, domestic courts inevitably make law. Courts do so with respect to the relationship between domestic and international law, but also regarding the content of international law, subject to the framework established by art. 38 icj Statute. Second, in this chapter I am not yet evaluating domestic courts’ activity. My goal, at this stage, is to clarify the legal consequences of their rulings in international law. Third, I analyze this effect in general terms, without focusing on particular norms and domains of international law. However, the effect of domestic rulings varies depending on the norm and substantive area of international law at stake.835 Fourth, I focus on the effect of domestic rulings in international law. The effect of Swiss courts’ rulings in domestic law is addressed in Chapter 3 (supra). Fifth, the way international law is received in domestic legal orders is contingent on domestic law (Chapter 3, supra). These features may limit domestic courts’ contribution to the sources of international law.

I now turn to the two legal effects of domestic rulings in international law, namely to their connecting (infra, section 2) and dynamic effect (infra, section 3).

2 Domestic Rulings as Means of Enforcement of International Law

A first legal effect of domestic judicial decisions on international law is that they facilitate the reception of international law in the domestic legal order. By enforcing international law domestically, they allow States to respect their international obligations (subject, of course, to the constraints established by domestic law in this respect, Chapter 3, supra).

International law, qua law, aims at being obeyed. This claim is implicit in all international legal norms, and explicit in some of them. For instance, the customary principle pacta sunt servanda codified in art. 26 vclt provides that States must honor their treaty obligations. States cannot in principle rely on domestic law to justify a violation of these treaty obligations (art. 27 vclt).836 States must also respect cil and general principles of international law qua sources of international law (art. 38 icj Statute), unless these States are excluded from the scope of their legal authority.837

A State’s violation of its international obligations triggers its international responsibility. The conditions of this responsibility are exclusively defined by international law.838 The ilc’s Draft Articles on State Responsibility for Internationally Wrongful Acts (arsiwa), most of which are customary,839 provide that State responsibility arises whenever the State commits an internationally wrongful act,840 ie, an act incompatible with its international obligations.841 The decision of a domestic court is always attributable to the State, even when it exceeds the court’s competence under domestic law.842 Thus, if domestic rulings fail to respect the State’s international obligations, they trigger their State’s international responsibility and its duty to provide reparation.843

One corollary of States’ duty to obey international law is their duty to apply and enforce international law domestically through their organs, so that international law can rule.844 International law is weakly institutionalized and lacks an international police force. Therefore, it must primarily rely on the State for its domestic enforcement.845 Exceptionally, international law defines the modalities of its enforcement, eg in ihrl,846 or in the context of remedies for breaches of international law.847

States’ duty to obey international law may be expressed or reinforced by more specific positive international legal duties, rights, or powers.848 The terminology used in international law to characterize these duties or competences is diverse and often inconsistent (eg the duty or competence to ‘enforce’, ‘apply’, ‘interpret’, ‘implement’, or ‘give effect’ to international law, to ‘monitor’ its application, etc.), which makes it necessary to interpret each provision to determine its legal implications. In some cases, international law explicitly requires or empowers States not only to give effect to their international obligations domestically, but also to interpret them.849

The domestic judicial application and enforcement of international law is sometimes explicitly mandated by international law. ihl for instance tasks domestic institutions, including courts,850 with its enforcement. Other examples include icl851 or ihrl.852 In international environmental law, access to courts is sometimes explicitly mandated.853 The icj has occasionally required that specific measures be taken by domestic courts to guarantee domestic compliance with international law,854 although domestic judges have sometimes shown resistance.855

While some authors argue that international law increasingly imposes duties upon domestic organs,856 conceptually, it is the State’s (and not domestic courts’) international legal duty to respect international law.857 States are free to choose the means by which to give effect to their international obligations. However, the nature and content of some obligations may require that States take certain measures to ensure that their courts will give effect to international law.

States’ duty to abide by international law, and thus to implement it domestically and to act as ‘officials of international law’,858 explains why scholars highlight that domestic courts can, do, and/or should act as ‘enforcers’,859 ‘agents’,860 or ‘faithful trustees’861 of international law. Scholars describe domestic courts as the ‘first port of call’862 to adjudicate international legal issues and, when international adjudication is unavailable, as the first and only locus of international legal interpretation.863

Of course, the State’s duty to enforce international law via its organs may conflict with other duties under domestic and especially constitutional law. From the perspective of international law, domestic law is no valid justification for disregarding international law, including its interpretative methods.864 In such cases, courts experience a ‘double bind’,865 as they must respect two irreconcilable legal duties of the State. These conflicts faced by domestic courts have spilt a lot of ink, although it is important to highlight that in many instances, the conflict exists not only between international and domestic law, but also within domestic law.866 Scholars have highlighted ‘patterns of national contestation’ of international law, patterns which domestic courts contribute to tracing.867 Yet domestic courts also resolve conflicts by giving preference to what international law requires. In most areas of international law, contestation is the exception rather than the rule.868

Existing scholarship on conflicts between domestic and international law is chiefly descriptive, in the sense that it primarily maps the existing practice and rarely examines how domestic courts must (or should) resolve conflicts. This question is complex, because the answer to it depends on the provisions at stake and, importantly, hinges on considerations of moral and political philosophy. The issue of how conflicts must (or should) be resolved is beyond the scope of my study, but my account has implications for how courts must handle such conflicts. The thesis I defend is that courts must use specific methods to ascertain international law (ie, textual, systematic, purposive and, if applicable, historical interpretation), and that they should strive to reason predictably, clearly, and consistently. They must do so regardless of how they resolve clashes between domestic and international law.

3 Domestic Rulings as Contributors to the Sources and Interpretation of International Law

States’ duty to apply and enforce international law domestically, including via their courts, is not the only reason why domestic courts’ interpretations are central to international law. First, from the perspective of the sources of international law, domestic rulings can collectively contribute to the formation and modification of international law (infra, 3.1). Second, from the perspective of any domestic or international interpreter of international law, domestic judicial decisions are auxiliary means (or ‘subsidiary means’, as per art. 38(1)(d) icj Statute) that assist her in her interpretative task (infra, 3.2). Of course, domestic rulings have an analogous effect in domestic legal orders (supra, Chapter 3, 4.2.7). They can even, under certain conditions and in some States, exercise domestic legal authority beyond the particular case. Yet in this section, I focus on the place of domestic rulings in international law.

While domestic and international law increasingly overlap in terms of their respective subject matters and of the authorities that apply them, international and domestic lawmaking processes remain distinct (supra, Chapter 1, section 6). Even this distinction is not as sharp as it might seem, however. The sources of domestic and international law are intertwined due to the fact that States have the power to collectively create international law. When two or more States conclude a treaty, for instance, they make international law.869 States also collectively provide evidence of the two constitutive elements of cil, State practice and opinio juris. Furthermore, their acts can be a manifestation of the domestic recognition of at least some general principles of international law, ie, those applied in foro domestico. What differs between domestic and international lawmaking processes is that the latter involve States qua primary lawmakers.

The place of domestic rulings in the sources of international law is ambiguous in practice and in scholarship. While there is agreement (and rightly so) that domestic rulings are not a source of international law (infra, 3.1.13.1.3),870 their precise categorization is often left open (see also supra, Chapter 1, 2.3). Legal scholars and practitioners often mention that domestic courts ‘contribute’ to the ‘development’ of international law,871 or that they may ‘facilitate the determination of the contents of [international] obligations’.872 They consider that their rulings ‘may be relevant’ from the perspective of the identification of international law.873 The ila Study Group on Domestic Courts notes that domestic courts, ‘as organs of the State, necessarily affect the content of norms of international law whenever they engage with them. They serve as agents of development (or corrosion and decay) of international law norms’.874 The role of domestic courts as ‘agents of development’875 of international law has been highlighted with regard to general international law (eg the law of international responsibility876 or the international law of jurisdiction),877 ihl,878 icl,879 and ihrl.880 Scholars have also discussed the role domestic courts can play in ‘closing gaps’ in international law, for instance in the law of immunities.881

Although most international lawyers acknowledge a de facto ‘influence’ of domestic rulings on international law, domestic judicial lawmaking is often obfuscated or presented as an oblique phenomenon. Hersch Lauterpacht has probably endorsed the boldest position in this respect, suggesting that their decisions are a ‘source’ of international law.882 Only few scholars use such forceful terminology.883 Apart from these exceptions, the reluctance to deem domestic rulings authoritative on the international plane likely goes back to the controversial nature of judicial lawmaking in domestic law (infra, Chapter 5, 4.2). Moreover, as previously mentioned, the entrenchment of domestic rulings in art. 38 icj Statute is equivocal. Finally, the effect of domestic courts’ interpretation on the formation and evolution of international law is not monolithic. It depends on the source of international law at stake, on whether the scope of a given norm is inter- or intrastate, on whether mechanisms of international adjudication restrict domestic courts’ interpretative freedom and, of course, on courts’ rights, duties, and authority in domestic law.884 Therefore, the effect of these rulings must be assessed carefully.

In this section, my goal is to show that domestic rulings, despite States’ and international lawyers’ reluctance to acknowledge it, contribute to the formation, modification, and ascertainment of international law. I analyze the legal effect of these rulings with regard to treaty law (3.1.1), cil (3.1.2), and general principles of international law (3.1.3). I also highlight the assistance domestic rulings provide to other interpreters in future interpretations of international law, pursuant to art. 38(1)(d) icj Statute (3.2).885

Of course, domestic rulings also constitute State practice in a different respect, on which I do not focus here: like every act of a State organ, they are attributable to the State for the purposes of international responsibility.886

3.1 Domestic Rulings in the Sources of International Law (Art. 38(1)(a)–(c) icj Statute)

3.1.1 Treaties

Art. 31–33 vclt are widely held to codify the cil of treaty interpretation (on this issue, see infra, Chapter 6). Of particular interest for the purposes of this study is art. 31(3)(b) vclt, which states that ‘There shall be taken into account, together with the context [of the treaty]: […] b. Any subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation’.

The ilc’s Special Rapporteur on ‘subsequent agreements and subsequent practice’, Georg Nolte, addressed the ‘legal significance’ of domestic case law in a report published in 2016.887 Nolte merely observes that domestic rulings qua subsequent practice ‘do not raise specific problems’.888 Indeed, given that such rulings are attributable to the State,889 they can, together with other instances of domestic and foreign State practice, constitute subsequent practice in the sense of art. 31(3)(b) vclt.890 This constitutive aspect is arguably less central for treaty law than what is the case with cil, as custom cannot exist without its constitutive elements, namely State practice and opinio juris. This also explains why domestic judicial decisions are described by the ilc as elements providing evidence of State practice of opinio juris,891 contrary to the terminology that is typically used to describe the contribution of domestic rulings to the identification of treaty law and general principles of international law. Still, subsequent practice, when it exists, forms an integral, constitutive part of treaty law too.

This link between domestic rulings and subsequent practice is also reflected in the practice of international law. International criminal tribunals in particular have referred to domestic rulings qua subsequent practice,892 albeit not always explicitly. Two examples of implicit versus explicit references to subsequent treaty practice mentioned by André Nollkaemper are the rulings of the icty Trial Chamber in Krstić and Jelisić.893 In Krstić, the Chamber referred to art. 31 f vclt when ‘look[ing] for guidance in the practice of States, especially their judicial interpretations and decisions’.894 In Jelisić, it mentioned that it had ‘taken into account’ ‘[t]he practice of States, notably through their national courts’ after citing the vclt’s treaty interpretation provisions.895 It referred (without providing any details) to the Eichmann ruling of the Supreme Court of Israel, as well as to judgments of Equatorial Guinean, Vietnamese, Ethiopian, and German courts.896 While the Chamber did not mention art. 31(3)(b) vclt in Krstić, it did note the relevance of domestic courts qua ‘subsequent practice’ in Jelisić.897

The ilc commentary to the vclt does not specify how subsequent practice is to be ascertained. However, art. 31(3)(b) vclt makes it clear that domestic rulings reflect subsequent treaty practice if they establish the understanding of the parties. Hence, they cannot merely be a manifestation of the unilateral (auto-)interpretation of the treaty by one State. It is not necessary for the practice to express the understanding of all the parties, however, as the word ‘all’ was deliberately omitted by the ilc in the drafting process.898

International lawyers often limit themselves to general remarks as to the requirements this practice must fulfill to be relevant from the perspective of the vclt, eg that it must reflect ‘a certain constant pattern of state conduct’.899 To ensure predictability, clarity, and consistency in the way subsequent practice is ascertained, it seems helpful to interpret the notion of practice of art. 31(3)(b) vclt in light of the notion of State practice in cil. Like State practice in cil (see also infra, 3.1.2), subsequent treaty practice must reach a minimal threshold of coherence (or uniformity), constancy (or regularity), and generality (or representativeness).900 Otherwise, it cannot express the parties’ understanding. These requirements (coherence, constancy, generality) entail that domestic rulings, to constitute subsequent practice, must (i) not contradict the practice of other State organs (so that the practice is coherent), (ii) not be isolated rulings, but belong to an established practice, and (iii) emanate from the courts of a sufficiently large number of States. The requirements are even stricter for multilateral treaties.901 Of course, some differences with State practice in cil do exist. Subsequent treaty practice pertains to the interpretation of written norms upon which the parties have previously agreed, and it must establish ‘the agreement of the parties’ (art. 31(3)(b) vclt).

Assessing whether the aforementioned conditions are fulfilled indisputably involves discretion. International courts have not always been careful when ascertaining subsequent practice on the basis of domestic rulings.902 It is also important to note, along with Samantha Besson, that ‘the effects of domestic courts’ judicial interpretation on the interpreted norm [ie, on customary international legal norms and general principles] are greater than they are in the case of treaties’903 because of the process through which these norms are created and changed. This explains why domestic courts have been relatively neglected in the ascertainment of subsequent treaty practice. Nonetheless, domestic rulings can be constitutive of this practice and must be examined carefully.

3.1.2 Customary International Law

Besides reflecting subsequent treaty practice (supra, 3.1.1), domestic rulings can help determine (or, to use the ilc’s terminology,904 provide evidence of) State practice and/or opinio juris, the two constitutive elements of cil.905

As previously pointed out, the contribution of domestic judicial decisions to the formation and evolution of cil is more central than with respect to treaties (supra, 3.1.1) and general principles (infra, 3.1.3). Indeed, the very existence of custom depends on the presence of its constitutive elements. Treaties, by contrast, exist before a subsequent treaty practice develops. The absence of such a practice does not yield the conclusion that there is no treaty norm. As regards general principles, their domestic recognition does not suffice to establish their existence in international law, which must be determined through analogical reasoning. Moreover, some general principles of international law exist regardless of their recognition in foro domestico (on these two types of general principles, see infra, 3.1.3).

When do domestic rulings provide evidence of State practice and/or opinio juris in the context of cil? The ilc’s recent work on custom shows that many aspects of the identification of cil remain unsettled. Still, some are widely established. State practice and opinio juris must satisfy the requirements of coherence (or uniformity), constancy (or regularity), and generality (or representativeness).906 The terminology used to refer to these different requirements is highly inconsistent,907 however, and the practice (both domestic and international) tends not to take them seriously enough (infra, Chapters 6 and 8).908

The ilc cites domestic rulings among the forms of evidence of both State practice and opinio juris.909 The Special Rapporteur’s analysis of the authority of domestic rulings from the perspective of cil is very brief, and he only mentions their relevance qua State practice.910 In 2016, the ilc’s Secretariat conducted a comprehensive survey of international courts’ reliance on domestic rulings to identify custom.911 Indeed, international courts such as the pcij and its successor, the icj,912 the ictr,913 and especially the icty,914 have referred to domestic rulings qua State practice and/or opinio juris. Courts seldom distinguish between the two constitutive elements of cil in this context.915 As the ilc Secretariat notes, some never refer to domestic rulings when identifying cil, eg the itlos916 or the wto Appellate Body.917 Domestic rulings are typically one piece of evidence among others which courts use to determine the existence of cil.918 The domestic practice also occasionally uses domestic rulings qua evidence of the constitutive elements of cil, ie, State practice and opinio juris.919 Scholars accept this as well,920 although some emphasize State practice only.921

Domestic case law is, of course, not the only basis for ascertaining cil.922 When it is inconsistent, scarce, or not representative of a longa consuetudo, other instances of domestic (legislative or executive) practice and/or opinio juris may be used. The lack of domestic ‘judicial custom’923 is thus not necessarily the end of the matter with regard to cil.

Should rulings that conflict with the position of the other branches of government be deemed an expression of State practice and/or opinio? While some consider that what is decisive is whether the body at stake has the final authority on a given issue under domestic law924 (which is not always clear,925 see eg Chapter 3, 2.1.2 and 4.2.2, supra), others give preference to the executive’s view.926 The ila Study Group on Domestic Courts considers that domestic rulings, to constitute State practice and/or opinio, must be accepted (or ‘not “rejected”’,927 as the Study Group puts it) by the executive. The ilc, on the other hand, states that domestic judgments ‘will count less if they are reversed by the legislature or remain unenforced because of concerns about their compatibility with international law’.928 Yet it seems that especially when it comes to ascertaining opinio juris,929 ie, the fact that an act is performed out of a sense of legal obligation, judicial decisions should carry more weight than the acts of other State organs.930 Indeed, courts’ institutional position requires them to base their rulings on legally relevant (as opposed to strategic)931 reasons. It is worth stressing that this question arises if courts contradict the executive or the legislature, and vice versa, which is atypical in Switzerland (supra, Chapter 3, 4.2.2).

3.1.3 General Principles of International Law

Besides treaties and cil, another source of international law consists in the ‘general principles of law recognized by civilized nations’ (art. 38(1)(c) icj Statute).932 The German translation of the icj Statute uses the term ‘Kulturvölker’. The term ‘civilized’ reflects an imperialistic view of international law.933 It needs to be deleted given the commitment of international law to sovereign equality. However, proposals to amend the Statute in this sense have been unsuccessful.934

Unlike the ‘subsidiary means’ of art. 38(1)(d) icj Statute, general principles are a source of international law, but they are often considered of secondary importance compared to treaties and custom. They are deemed ‘gap-fillers’ that come into play when an issue is left open by other sources.935 General principles are of two types: some are idiosyncratic to international law (like sovereign equality), while others originate from domestic practices (like good faith).936 In the present study, the latter type of general principles, identified in foro domestico, is of particular interest.

How to identify general principles of domestic origin (ie, ‘general principles of law’, as opposed to ‘general principles of international law stricto sensu’)937? While general principles of this kind are ‘traced to state practice’,938 including to ‘judicial law’,939 it is important to note that this requirement of a practice of recognition is looser than the test applied to identify State practice and opinio juris in cil. The existence of general principles of law primarily hinges on their recognition by States.

International courts (eg in icl or ihrl) have identified general principles of law on the basis of national practices through analogical and/or comparative legal reasoning, although the methods they employ are not always transparent and comprehensive.940 Sometimes, they have used domestic court decisions.941 In general, however, the pcij and icj rarely apply general principles as a source of international law.942 The icty has been cautious in using domestic case law to ascertain general principles of international law. In Tadić, it deemed reliance on ‘national legislation and case law’ justified only if ‘most, if not all, countries adopt the same notion of common purpose’. The court added that ‘it would be necessary to show that, in any case, the major legal systems of the world take the same approach’ to the issue at stake.943 Yet referring to so-called ‘major legal systems’ is problematic, as more weight is given to some States based on opaque criteria. As a matter of fact, Nollkaemper notes that the icty uses domestic case law selectively to identify general principles of international law.944

To conclude, domestic rulings help determine States’ recognition of general principles of law. The weight of these rulings depends on how they fit with other domestic legislative and executive practices, analogously to what applies to cil (supra, 3.1.2). The two-tiered test of State practice and opinio juris used for cil does not need to be satisfied for general principles, which merely have to be ‘general’ and ‘recognized’ domestically.945 This does not mean that such principles can be invoked to circumvent the two-tiered test of cil.946

3.2 Domestic Rulings as Auxiliary Means (Art. 38(1)(d) icj Statute)

If in a given case, domestic rulings do not fulfill the criteria of subsequent treaty practice, State practice, and/or opinio juris in the context of cil, or the domestic practice of recognition that generates some general principles of international law (supra, 3.1), domestic case law may still be used qua ‘subsidiary means for the determination of rules of [international] law’ (art. 38(1)(d) icj Statute).947 I prefer to call them auxiliary means, for reasons I set out below. The use of domestic rulings qua auxiliary means pursuant to art. 38(1)(d) icj Statute by interpreters of international law stands on a different level than these rulings’ contribution to the sources of international law of art. 38(1)(a)–(c) icj Statute (supra, 3.1).948 While the difference is frequently blurred in practice,949 distinctive tests apply in these two contexts.

The uncertainties surrounding art. 38(1)(d) icj Statute and, more generally, the place of judicial decisions in the sources of international law, reflect the amour impossible950 between the orthodox doctrine of the sources of international law and the effect judicial decisions (both domestic and international) have in practice (supra, Chapter 1, 2.3).951 Given the practical significance of judicial decisions in international law, scholarly analyses of art. 38(1)(d) icj Statute are surprisingly scarce.952 International lawyers often mention the provision in passing, without analyzing the legal authority of domestic rulings.

International lawyers generally agree that ‘subsidiary means’ are conceptually distinct from the sources of international law listed in art. 38(1)(a)–(c) icj Statute.953 On the other hand, judicial decisions are sometimes qualified as an ‘indirect source’954 or a ‘subsidiary source’.955 These expressions are misleading: either something is a source of law, or it is not. ‘Subsidiary means’ are not sources, but material that assists decision-makers in ascertaining norms stemming from the sources of international law. The term ‘subsidiary means’ erroneously suggests a hierarchy or chronological priority between sources and ‘subsidiary means’,956 instead of acknowledging that the latter help ‘elucidate’957 the former.958 Because judicial decisions are auxiliary means, they cannot usurp the authority of the ‘antecedent source’ of the law they ‘propound’.959 As noted by the Asian-African Legal Consultative Organization (aalco), they are ‘no more than guideposts on the road to the destination, not the destination itself’.960 In this regard, the French version of the icj Statute is more precise than the English one, as it refers to ‘auxiliary’ means, ie, to means that are ‘offering or providing help’.961 Hence, the term auxiliary means seems more appropriate (see also supra, Chapter 2, 5.4).962

While there are exceptions,963 most international lawyers consider domestic rulings to fall under the ‘subsidiary means’ of art. 38.964 This view is reflected in the ilc’s draft conclusions on cil.965 It is supported by the fact that in the drafting process of the pcij Statute, the initial reference to international judicial decisions was changed to ‘judicial decisions’.966 Moreover, especially in the context of cil, international courts967 and arbitral tribunals968 seem to use domestic rulings qua auxiliary means, even if they do not always explicitly say so.969 As mentioned, it is often unclear in practice whether such rulings are cited based on art. 38(1)(d) icj Statute, or qua element of determination of international law.970

The word ‘subsidiary’, according to André Nollkaemper, ‘reflects the fact that no formal system of precedents exists [in international law], let alone a principle of stare decisis’.971 Absent such doctrines, however, interpreters are left with little guidance as to the weight of domestic rulings. Yet relying on domestic rulings in an erratic way stands in a tension with lawful, predictable, clear, and consistent judicial reasoning.972 Domestic judicial decisions are not a convenient ‘shortcut’ or ‘a “quick fix” solution’.973 They are interpretative aids that should be used with ‘intellectual discipline’,974 not based on convenience or result-oriented cherry-picking.

International lawyers explain that in practice, judicial decisions are usually relied on ‘for their persuasive value’.975 Alain Pellet and Daniel Müller for instance write:

[P]recisely as ‘there are awards and awards, some destined to become ever brighter beacons, others to flicker and die near-instant deaths’, there are judgments and judgments. Central to the question is the persuasiveness of the legal reasoning.976

The notion of persuasive authority is frequently used in common law countries. Grant Lamond defines it as ‘non-binding but legally relevant considerations’.977 As Lamond explains, persuasive authority is a theoretical type of authority. It provides reasons to believe X, as opposed to reasons to do X, which is characteristic of practical authority.978

The notion of persuasiveness can be misleading. It can for example suggest that a decision is cited and followed in later cases simply because of its rhetorical force. Persuasiveness does not capture the fact that some judgments are cited in later cases (and hence have a legal effect beyond the particular case) because they are considered to offer lawful, high-quality reasoning. In this context, Samantha Besson’s distinction between decisional and interpretive authority is helpful. According to Besson, judicial decisions have ‘decisional authority’ for the parties to the dispute, but also, in some cases, ‘interpretive authority’ by guiding future interpretations of the law.979

In relation to this issue, it is important to note that the question of other interpreters’ (subjective) reliance on a given judgment (as authorized by art. 38(1)(d) icj Statute) is distinct from the question of the place of this judgment in the sources of international law (eg in international law, with respect to art. 38(1)(a)–(c) icj Statute, supra, 3.1). It also differs from the question of the (objective) legal authority of this ruling, be it vis-à-vis its addressees, in the legal order, or for a given court (qua precedent).

When should domestic rulings be used as auxiliary means pursuant to art. 38(1)(d) icj Statute? The answer partly follows from the two criteria I use to evaluate the practice of domestic courts (supra, Introduction, section 3). One criterion is courts’ use of the interpretative methods of international law, as it indicates that a decision was made in conformity with what the law requires. A second one is the quality of the court’s reasoning.980 As mentioned, the predictability, clarity, and consistency of judicial decisions are indicators of high-quality legal reasoning. They suggest – but do not guarantee – that the interpretation was not reached on a whim, but after a careful, thorough examination. Third, domestic case law that is not well established provides scant support for a given solution. In this context, the requirements of coherence, constancy, and generality of State practice in the context of cil offer guidance. These requirements are not decisive, however, and may need to be relativized when the case law on a given issue is limited. Fourth, domestic rulings that have been quashed or contradicted by higher domestic courts carry little weight, even if the requirement of internal consistency applicable in the context of cil does not strictly apply to auxiliary means. By contrast, the warrant of rulings that have withstood the test of higher judicial instances is stronger. Fifth, the domestic context of the judicial decision must be taken into account, including the court’s jurisdiction, its composition, resources, and expertise (see also the criteria highlighted in Chapter 3, supra). These characteristics especially help determine whether the court’s reasoning is generalizable. Sixth, obiter dicta arguably carry less weight than the ratio decidendi.

While the aforementioned criteria are not exhaustive and do not offer hard and fast rules on when domestic rulings provide conclusive auxiliary means, they provide guidelines for this assessment.

4 Conclusion

I have argued that domestic rulings on international law are central to international law in two main respects. First, domestic courts, through their interpretations, can enforce international law domestically and avert their State’s international responsibility (supra, section 2). Second, they can (collectively) contribute to the formation and evolution of international law, and hence provide indications as to its content (supra, 3.1), and they can be used by interpreters of international law qua auxiliary means (supra, 3.2).

Since domestic rulings, besides having domestic legal authority (supra, Chapter 3, 4.2.7), are central to international law in these two respects, it is important to clarify the international legal frame that constrains domestic courts’ interpretations. Part 3 of this study is devoted to this question, which overlaps with Raz’s third question on interpretation, namely: how to interpret?

816

Raz, Between Authority and Interpretation: On the Theory of Law and Practical Reason (n 78) 224 f.

817

I develop this further in Odile Ammann, ‘How Do and Should Domestic Courts Interpret International Law? Insights From the Jurisprudence of H.L.A. Hart and Duncan Kennedy’ (2019) Transnational Legal Theory (forthcoming).

818

On this issue, see Besson, ‘Human Rights’ Adjudication as Transnational Adjudication: A Peripheral Case of Domestic Courts as International Law Adjudicators’ (n 56) 48 ff.

819

Raz, Between Authority and Interpretation: On the Theory of Law and Practical Reason (n 78) 223.

820

Barradas de Freitas (n 127) 45. See also ibid 273 ff. Barradas argues that interpretation plays an instrumental role in that it makes the exercise of legal authority possible. By making the law intelligible, it helps individuals understand what the law requires, and hence be guided by it. See ibid 278.

821

Joseph Raz states that understanding the importance of legal interpretation is necessary ‘to evaluate the different [philosophical] accounts of legal interpretation’ provided by legal theorists. See Raz, Between Authority and Interpretation: On the Theory of Law and Practical Reason (n 78) 225.

822

Weill (n 61); Sloss (n 120); Jonathan I Charney, ‘International Criminal Law and the Role of Domestic Courts’ (2001) 95 American Journal of International Law 120; Henry G Schermers, ‘The Role of Domestic Courts in Effectuating International Law’ (1990) 3 Leiden Journal of International Law 77; Falk (n 50); Bradley and Goldsmith (n 171) ch 2.

823

This observation has been made by Besson, ‘Human Rights’ Adjudication as Transnational Adjudication: A Peripheral Case of Domestic Courts as International Law Adjudicators’ (n 56) 45.

824

See ibid 45 ff.

825

See ibid 47 f.

826

Besides the sheer quantity of contributions that have dealt with this topic, the terminologies, taxonomies, and theoretical approaches used to analyze what domestic courts do, must do, or should do when interpreting international law are diverse and sometimes intermingled. For an overview, see ibid 45 ff.

827

ila, ‘Preliminary Report of the ila Study Group on Principles on the Engagement of Domestic Courts With International Law’ (n 61); ila, ‘Working Session Report of the ila Study Group on Principles on the Engagement of Domestic Courts With International Law’ (n 61); ila, ‘(Study Group on) Principles on the Engagement of Domestic Courts With International Law, Final Report: Mapping the Engagement of Domestic Courts With International Law’ (n 15).

828

Eg Weill (n 61) 179.

829

An early advocate of the ‘functional approach’ is Philip Jessup, ‘The Functional Approach as Applied to International Law’, Proceedings of the Third Conference of Teachers of International Law (Carnegie Endowment 1928).

830

Gleider Hernández, The International Court of Justice and the Judicial Function (Oxford University Press 2014).

831

One illustration is provided by the concepts of ‘translation’ and ‘soft originalism’ used by some us constitutional legal scholars. On translation, see Lawrence Lessig, ‘Understanding Changed Readings: Fidelity and Theory’ (1995) 47 Stanford Law Review 395; Lawrence Lessig, ‘Translating Federalism: United States v Lopez’ (1995) 1995 Supreme Court Law Review 125. On soft originalism, see Cass R Sunstein, ‘Five Theses on Originalism’ (1995) 19 Harvard Journal of Law & Public Policy 311. For a critique, see Michael J Klarman, ‘Fidelity, Indeterminacy, and the Problem of Constitutional Evil’ (1997) 65 Fordham Law Review 1739, 1753 ff.

832

This point has been brought to my attention by Michael Klarman.

833

On these two facets, see Edouard Dubout and Sébastien Touzé, ‘La fonction des droits fondamentaux dans les rapports entre ordres et systèmes juridiques’ in Edouard Dubout and Sébastien Touzé (eds), Les droits fondamentaux : charnières entre ordres et systèmes juridiques (Pedone 2009); Besson and Ammann (n 60) 7–9.

834

Tzanakopoulos and Methymaki (n 217). See also Antonios Tzanakopoulos, ‘Domestic Courts in International Law’ (United Nations Audiovisual Library of International Law, 2016) <legal.un.org/avl/ls/Tzanakopoulos_IL_video_1.html>.

835

Besson, ‘Human Rights’ Adjudication as Transnational Adjudication: A Peripheral Case of Domestic Courts as International Law Adjudicators’ (n 56) 47 f.

836

See also pcij, case concerning the GrecoBulgarian ‘Communities’, advisory opinion, pcij Series B No 17, 31 July 1930, 4, at 32. States cannot even rely on constitutional law: pcij, case concerning the Treatment of Polish Nationals and Other Persons of Polish Origin or Speech in the Danzig Territory, advisory opinion, pcij Series a/b No 44, 4 February 1932, 3, at 24; icj, case concerning Avena and Other Mexican Nationals (Mexico v. United States), judgment, icj Reports 2004, 31 March 2004, 12, at 65, para 139.

837

Eg if States are persistent objectors to a given norm of cil, or in the case of regional custom.

838

icj, case concerning Elettronica Sicula SpA (elsi) (United States v. Italy), judgment, icj Reports 1989, 20 July 1989, 15, at 51, para 73.

839

Some arsiwa provisions remain contested, such as those on serious breaches and countermeasures: James Crawford, ‘State Responsibility’, Max Planck Encyclopedia of Public International Law (Online Edition) (Oxford University Press 2006) 65 <opil.ouplaw.com>.

840

Art. 1 arsiwa.

841

Art. 12 arsiwa.

842

Art. 4, 7 arsiwa.

843

pcij, case concerning the Factory at Chorzów (Germany v. Poland), judgment, claim for indemnity, merits, pcij Series A No 17, 13 September 1928, 4, at 29.

844

Leo Gross, ‘States as Organs of International Law and the Problem of Autointerpretation’, Essays on International Law and Organization (Vol I) (Transnational Publishers, Inc/Martinus Nijhoff 1984) 378 f.

845

Even international judges play a limited role with regard to enforcement, see Besson, ‘Legal Philosophical Issues of International Adjudication: Getting Over the Amour Impossible Between International Law and International Adjudication’ (n 85) 425. Some international bodies monitor the domestic enforcement of international law. One example is the Committee of Ministers of the Council of Europe, which monitors the domestic enforcement of ECtHR rulings, see Samantha Besson, ‘Les effets et l’exécution des arrêts de la Cour européenne des droits de l’homme – Le cas de la Suisse’ in Bernhard Ehrenzeller and Stephan Breitenmoser (eds), Die emrk und die Schweiz / La cedh et la Suisse (Schulthess 2010) 160 ff.

846

Frédéric Mégret, ‘Nature of Obligations’ in Daniel Moeckli, Sangeeta Shah, and Sandesh Sivakumaran (eds), International Human Rights Law (Oxford University Press 2014) 101 ff.

847

icj, case concerning Avena and Other Mexican Nationals (Mexico v. United States), judgment, icj Reports 2004, 31 March 2004, 12, at 59 f, para 121.

848

Besson, ‘Human Rights’ Adjudication as Transnational Adjudication: A Peripheral Case of Domestic Courts as International Law Adjudicators’ (n 56) 47.

849

See ibid. The echr for instance is primarily interpreted by State institutions.

850

See art. 49(2), art. 50(2), art. 129(2), and art. 146(2) of the four Geneva Conventions of 1949, respectively. On requirements of domestic enforcement in general, see Weill (n 61) 7 foonote 17.

851

Art. 1 icc Statute. See also art. vi of the Genocide Convention of 9 December 1948.

852

Eg art. 2(3) iccpr. The un treaty bodies have stressed the importance for States to grant judicial remedies, so that individuals can invoke relevant international human rights obligations. See the examples mentioned by Künzli, Eugster, and Spring (n 442) 4, note 6.

853

Art. 9 Aarhus Convention. The importance of judicial review is also stressed in soft law instruments, eg the Johannesburg Principles on the Role of Law and Sustainable Development adopted at the Global Judges Symposium on 18–20 August 2002.

854

icj, case concerning Avena and Other Mexican Nationals (Mexico v. United States), judgment, icj Reports 2004, 31 March 2004, 12, at 59 f, para 121. See also Fikfak, ‘Reinforcing the icj’s Central International Role? Domestic Courts’ Enforcement of icj Decisions and Opinions’ (n 63).

855

A well-known example is the Avena/Medellín saga. On the other hand, some domestic courts explicitly underscore their State’s duty to apply international law domestically. The Swiss Federal Tribunal for instance, early on in its case law, emphasized the State’s duty to enforce international law through its institutions, eg bge 49 i 188, at 3. The Court especially highlights judicial enforcement with respect to ihrl. See bge 123 ii 595, at 7 c); bge 117 Ib 367, at 2 e).

856

Ward Ferdinandusse, ‘Out of the Black-Box? The International Obligation of State Organs’ (2003) 29 Brooklyn Journal of International Law 45.

857

This is also how the icj phrased the issue in the case concerning Avena and Other Mexican Nationals (Mexico v. United States), judgment, icj Reports 2004, 31 March 2004, 12, at 60, para 121. See also Tzanakopoulos and Methymaki (n 217) 6.

858

Jeremy Waldron, ‘Are Sovereigns Entitled to the Benefit of the International Rule of Law?’ (2011) 22 European Journal of International Law 315; Samantha Besson, ‘Sovereignty, International Law and Democracy’ (2011) 22 European Journal of International Law 373, 375.

859

Rodney Harrison, ‘Domestic Enforcement of International Human Rights in Courts of Law: Some Recent Developments’ (1995) 21 Commonwealth Law Bulletin 1290; Masters (n 331); Oona A Hathaway and Scott J Shapiro, ‘Outcasting: Enforcement in Domestic and International Law’ (2011) 121 Yale Law Journal 252; Roberts, ‘Comparative International Law? The Role of National Courts in Creating and Enforcing International Law’ (n 59); Susan Deller Ross, ‘Enforcing Women’s International Rights at Home: International Law in Domestic Courts’, Women’s Human Rights: The International and Comparative Law Casebook (University of Pennsylvania Press 2008); M Shah Alam, ‘Enforcement of International Human Rights Law by Domestic Courts in the United States’ (2004) 10 Annual Survey of International and Comparative Law 27; Richard F Oppong and Lisa C Niro, ‘Enforcing Judgments of International Courts in National Courts’ (2014) 5 Journal of International Dispute Settlement 344; Dapo Akande and Sangeeta Shah, ‘Immunities of State Officials, International Crimes, and Foreign Domestic Courts’ (2011) 21 European Journal of International Law 815; Conforti and Francioni (n 120); Fikfak, ‘Reinforcing the icj’s Central International Role? Domestic Courts’ Enforcement of icj Decisions and Opinions’ (n 63); Weill (n 61) 117; Schermers (n 822); Karen Knop, ‘Here and There: International Law in Domestic Courts’ (2000) 32 New York University Journal of International Law and Politics 501, 501, footnote 1.

860

Nollkaemper, National Courts and the International Rule of Law (n 47) 8.

861

Eirik Bjorge, Domestic Application of the echr: Courts as Faithful Trustees (Oxford University Press 2015).

862

Nollkaemper, National Courts and the International Rule of Law (n 47) 11 f.

863

Tzanakopoulos, ‘Domestic Courts in International Law: The International Judicial Function of National Courts’ (n 57) 151.

864

Art. 27 vclt.

865

Nollkaemper, National Courts and the International Rule of Law (n 47) 14.

866

For an example, see bge 139 i 16.

867

Raffaela Kunz, ‘Judging International Judgments Anew? The Human Rights Courts Before Domestic Courts’ European Journal of International Law (forthcoming); Mikael Rask Madsen, Pola Cebulak, and Micha Wiebusch, ‘Backlash Against International Courts: Explaining the Forms and Patterns of Resistance to International Courts’ (2018) 14 International Journal of Law in Context 197; Machiko Kanetake and André Nollkaemper (eds), The Rule of Law at the National and International Levels: Contestations and Deference (Hart Publishing 2015). Curtis Bradley argues that the us Supreme Court is a ‘filter’ between international and us law that ensures that international law fits ‘the structure and values of the constitutional system’, see Bradley (n 70) 102. André Nollkaemper uses the metaphors of ‘safety valve[s] or gate-keeper[s]’, see Nollkaemper, National Courts and the International Rule of Law (n 47) 303. Harold Koh views domestic actors (including courts) as a ‘transmission belt’ which mediates between international law and the domestic legal order: Harold Hongju Koh, ‘Why Do Nations Obey International Law?’ (1997) 106 Yale Law Journal 2599, 2651. Contra Knop (n 859) 505.

868

Christopher McCrudden, ‘Why Do National Court Judges Refer to Human Rights Treaties? A Comparative International Law Analysis of cedaw’ (2015) 109 American Journal of International Law 534, 538.

869

Gross (n 844) 379.

870

Some courts explicitly reject the idea that domestic rulings do and/or should have legal authority (qua source) on the international plane: icj, ‘Public sitting held on Monday 12 September 2011, at 10 a.m., at the Peace Palace, President Owada presiding, in the case concerning Jurisdictional Immunities of the State (Germany v. Italy: Greece intervening)’, <www.icj-cij.org/docket/files/143/16677.pdf>, at 21, cited in Weill (n 61) 157. See also icty (Trial Chamber ii), Prosecutor v. Zoran Kupreškić and Others, trial judgment, Case No it-95-16-t, 14 January 2000, para 540, cited in Aldo Zammit Borda, ‘The Use of Precedent as Subsidiary Means and Sources of International Criminal Law’ (2013) 18 Tilburg Law Review 65, 69. Even national courts such as the uk House of Lords have pointed out that they should not make law for other subjects of international law, including other States. See Lord Hoffmann in Jones v. Ministry of Interior Al-Mamlaka Al-Arabiya AS Saudiya, (2006) ukhl 26, para 63, cited in Weill (n 61) 157.

871

Nollkaemper, National Courts and the International Rule of Law (n 47) 10; Tams and Tzanakopoulos (n 147); Veronika Fikfak, ‘Judicial Strategies and Their Impact on the Development of the International Rule of Law’ in Machiko Kanetake and André Nollkaemper (eds), The Rule of Law at the National and International Levels: Contestations and Deference (Hart Publishing 2016); Iovane (n 182); Harmen van der Wilt, ‘Domestic Courts’ Contribution to the Development of International Criminal Law: Some Reflections’ (2013) 46 Israel Law Review 207; Jennings (n 40); Venzke, How Interpretation Makes International Law: On Semantic Change and Normative Twists (n 126) 16. See also Devika Hovell, ‘A Dialogue Model: The Role of the Domestic Judge in Security Council Decision-Making’ (2013) 26 Leiden Journal of International Law 579, 592. For a legal practitioner’s view, see Gérard V La Forest, ‘The Expanding Role of the Supreme Court of Canada in International Law Issues’ (1996) xxxiv Canadian Yearbook of International Law 89, 100.

872

Nollkaemper, National Courts and the International Rule of Law (n 47) 10.

873

ilc Secretariat, ‘Identification of Customary International Law: The Role of Decisions of National Courts in the Case Law of International Courts and Tribunals of a Universal Character for the Purpose of the Determination of Customary International Law’ (n 185) 3, para 4.

874

ila, ‘Preliminary Report of the ila Study Group on Principles on the Engagement of Domestic Courts With International Law’ (n 61) 13.

875

Tams and Tzanakopoulos (n 147).

876

Simon Olleson, ‘Internationally Wrongful Acts in the Domestic Courts: The Contribution of Domestic Courts to the Development of Customary International Law Relating to the Engagement of International Responsibility’ (2013) 26 Leiden Journal of International Law 615. See however, with regard to State responsibility: Stephan Wittich, ‘Domestic Courts and the Content and Implementation of State Responsibility’ (2013) 26 Leiden Journal of International Law 643.

877

Roger O’Keefe, ‘Domestic Courts as Agents of Development of the International Law of Jurisdiction’ (2013) 26 Leiden Journal of International Law 541.

878

Yaël Ronen, ‘Silent Enim Leges Inter Arma – but Beware the Background Noise: Domestic Courts as Agents of Development of the Law on the Conduct of Hostilities’ (2013) 26 Leiden Journal of International Law 599.

879

van der Wilt (n 871).

880

Besson, ‘Human Rights’ Adjudication as Transnational Adjudication: A Peripheral Case of Domestic Courts as International Law Adjudicators’ (n 56); Iovane (n 182).

881

August Reinisch, ‘To What Extent Can and Should National Courts “Fill the Accountability Gap”?’ (2013) 10 International Organizations Law Review 572. See also Karel Wellens, ‘Fragmentation of International Law and Establishing an Accountability Regime for International Organizations: The Role of the Judiciary in Closing the Gap’ (2004) 25 Michigan Journal of International Law 1159.

882

Lauterpacht, ‘Municipal Decisions as Sources of International Law’ (n 50).

883

Hovell (n 871) 582, 591 ff. See also Jennings (n 40) 3 f. André Nollkaemper, in an article on icl, assesses whether domestic courts are ‘sources’ of international law: Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182).

884

Besson, ‘Human Rights’ Adjudication as Transnational Adjudication: A Peripheral Case of Domestic Courts as International Law Adjudicators’ (n 56) 48.

885

See already ibid 49 f.

886

Art. 4 arsiwa; ila Committee on Formation of Customary (General) International Law, ‘Final Report: Statement of Principles Applicable to the Formation of General Customary International Law’ (2000) 17 <www.ila-hq.org/index.php/committees?committeeID=22>.

887

ilc, ‘Fourth Report on Subsequent Agreements and Subsequent Practice in Relation to the Interpretation of Treaties by Georg Nolte, Special Rapporteur’ (2016) un Doc a/cn.4/694 36 ff para 95 ff.

888

See ibid 37 para 96.

889

Gerhard Hafner, ‘Subsequent Agreements and Practice: Between Interpretation, Informal Modification, and Formal Amendment’ in Georg Nolte (ed), Treaties and Subsequent Practice (Oxford University Press 2013) 113.

890

Rosanne van Alebeek, ‘Domestic Courts as Agents of Development of International Immunity Rules’ (2013) 26 Leiden Journal of International Law 559, 562; Marcin Kaldunski, ‘The Law of State Immunity in the Case Concerning Jurisdictional Immunities of the State (Germany v. Italy)’ (2014) 13 The Law and Practice of International Courts and Tribunals 54, 99; ilc Secretariat, ‘Identification of Customary International Law: The Role of Decisions of National Courts in the Case Law of International Courts and Tribunals of a Universal Character for the Purpose of the Determination of Customary International Law’ (n 185) 3 para 4; ila, ‘(Study Group on) Principles on the Engagement of Domestic Courts With International Law, Final Report: Mapping the Engagement of Domestic Courts With International Law’ (n 15) 3. See also Besson, ‘Human Rights’ Adjudication as Transnational Adjudication: A Peripheral Case of Domestic Courts as International Law Adjudicators’ (n 56).

891

Draft conclusions 6(2) and 10(2), ilc, ‘Draft Conclusions on Identification of Customary International Law, With Commentaries’ (2018) un Doc a/73/10 119.

892

ilc, ‘First Report on Subsequent Agreements and Subsequent Practice in Relation to Treaty Interpretation by Georg Nolte, Special Rapporteur’ (2013) un Doc a/cn.4/660 18 f para. 41.

893

Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 280.

894

icty (Trial Chamber i), Prosecutor v. Radislav Krstić, Case No it-98-33-t, judgment, 2 August 2001, para 541, cited by Nollkaemper, ibid.

895

icty (Trial Chamber), Prosecutor v. Goran Jelisić, Case No it-95-10-t, judgment, 14 December 1999, para 61, cited by Nollkaemper, ibid 279.

896

Ibid, para 61, footnote 80.

897

Ibid, para 61. See also Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 280.

898

ilc, ‘Draft Articles on the Law of Treaties With Commentaries’ (n 783) 222.

899

Hafner (n 889) 113.

900

On these three requirements: Besson and Ammann (n 60) 110 ff.

901

Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 280.

902

See ibid.

903

Besson, ‘Human Rights’ Adjudication as Transnational Adjudication: A Peripheral Case of Domestic Courts as International Law Adjudicators’ (n 56) 48.

904

Draft conclusion 3, ilc, ‘Draft Conclusions on Identification of Customary International Law, With Commentaries’ (n 891). The ilc notes that the term ‘evidence’ is to be understood in a broad sense, and that it does not refer to a formal procedure in which evidence is produced and assessed. See footnote 263, in ilc, ‘Report on the Sixty-Eighth Session (2 May–10 June and 4 July–12 August 2016)’ (2016) un Doc a/71/10 84.

905

Art. 24 ilc Statute states the following: ‘The Commission shall consider ways and means for making the evidence of customary international law more readily available, such as the collection and publication of documents concerning State practice and of the decisions of national and international courts on questions of international law […]’ (emphasis added).

906

Eg ila Committee on Formation of Customary (General) International Law (n 886) 20 ff; James Crawford, Brownlie’s Principles of Public International Law (8th edn, Oxford University Press 2012) 24 f. See also draft conclusions 7–8 in ilc, ‘Draft Conclusions on Identification of Customary International Law, With Commentaries’ (n 891).

907

For an attempted clarification: Besson and Ammann (n 60) 110 ff.

908

On the icty: Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 285. On the Swiss practice: Besson and Ammann (n 60).

909

ilc, ‘Draft Conclusions on Identification of Customary International Law, With Commentaries’ (n 891). See draft conclusions 5, 6(2), and 10(2).

910

ilc, ‘Second Report on Identification of Customary International Law by Special Rapporteur Sir Michael Wood’ (n 578) 42 para 58.

911

ilc Secretariat, ‘Identification of Customary International Law: The Role of Decisions of National Courts in the Case Law of International Courts and Tribunals of a Universal Character for the Purpose of the Determination of Customary International Law’ (n 185).

912

pcij, case concerning the s.s. ‘Lotus’ (France v. Turkey), judgment, pcij 1927 Series A No 10, 7 September 1927, 25 ff; icj, Jurisdictional Immunities of the State (Germany v. Italy; Greece intervening), judgment, icj Reports 2012, 3 February 2012, 99, at 122 f, para 55; 125, para 61; and especially 131 ff, para 72 ff; see also 141 f, para 96; 143, para 101.

913

See the ilc Secretariat’s remarks: ilc Secretariat, ‘Identification of Customary International Law: The Role of Decisions of National Courts in the Case Law of International Courts and Tribunals of a Universal Character for the Purpose of the Determination of Customary International Law’ (n 185) 28 ff para 44 ff.

914

As of 1 December 2015, the icty had referred to domestic rulings when identifying cil in 49 out of 81 rulings: ibid 21, para 36. See also Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 281 ff. For references to domestic case law, see icty (Appeals Chamber), Prosecutor v. Dražen Erdemović, judgment, Case No it-96-22-a, 7 October 1997, joint and separate opinion of Judge McDonald and Judge Vohrah, para 50 and 55; icty (Trial Chamber ii), Prosecutor v. Anto Furundžija, judgment, Case No it-95-17/1-t, 10 December 1998, para 194 ff; icty (Appeals Chamber), Prosecutor v. Duško Tadić, opinion and judgment, Case No it-94-1-t, 7 May 1997, para 641 f (where the Court deemed French case law ‘instructive’, but of lesser relevance given that it concerned domestic law).

915

ilc Secretariat, ‘Identification of Customary International Law: The Role of Decisions of National Courts in the Case Law of International Courts and Tribunals of a Universal Character for the Purpose of the Determination of Customary International Law’ (n 185) 22 f para 37 f.

916

See ibid 18 f para 31 ff. However, individual judges of the itlos have done so, see ibid 19, para 34.

917

See ilc Secretariat, ‘Identification of Customary International Law: The Role of Decisions of National Courts in the Case Law of International Courts and Tribunals of a Universal Character for the Purpose of the Determination of Customary International Law’ (n 185) 20, para 35.

918

Eg ibid 24, para 39.

919

Besson and Ammann (n 60) 77 f.

920

Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 281 f; Ingrid Wuerth, ‘International Law in Domestic Courts and the Jurisdictional Immunities of the State Case’ (2012) 13 Melbourne Journal of International Law 819, 3. See also Javier Dondé Matute, ‘International Criminal Law Before the Supreme Court of Mexico’ (2010) 10 International Criminal Law Review 571, 575.

921

ila Committee on Formation of Customary (General) International Law (n 886) 18. See also the following statement of the ila Study Group on Domestic Courts, in its 2014 Working Session Report: ‘The traditional position in international law is that domestic courts engage in state practice, and thus they effectively make international law, at least on a micro-level’. ila, ‘Working Session Report of the ila Study Group on Principles on the Engagement of Domestic Courts With International Law’ (n 61) 3.

922

Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 285.

923

Besson, ‘Human Rights’ Adjudication as Transnational Adjudication: A Peripheral Case of Domestic Courts as International Law Adjudicators’ (n 56) 60.

924

Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 284.

925

On the different approaches to conflicts between the judiciary and the executive, see Wuerth (n 920) 5, 10.

926

ila Committee on Formation of Customary (General) International Law (n 886) 18. On this question, see Wuerth (n 920) 3 ff.

927

ila, ‘(Study Group on) Principles on the Engagement of Domestic Courts With International Law, Final Report: Mapping the Engagement of Domestic Courts With International Law’ (n 15) 4.

928

ilc, ‘Draft Conclusions on Identification of Customary International Law, With Commentaries’ (n 891) 128 para 5.

929

Ingrid Wuerth suggests that courts’ institutional independence also justifies placing particular emphasis on their views to identify State practice: Wuerth (n 920) 19.

930

Eg ibid 9.

931

ila Committee on Formation of Customary (General) International Law (n 886) 5.

932

It is worth pointing out that, conceptually, it is these principles’ recognition (qua social fact) that constitutes a source of international law, not the principle itself.

933

On the imperialistic roots of international law, see eg Antony Anghie, ‘Finding the Peripheries: Sovereignty and Colonialism in Nineteenth-Century International Law’ (1999) 40 Harvard International Law Journal 1; Martti Koskenniemi, Walter Rech, and Manuel Jiménez Fonseca (eds), International Law and Empire: Historical Explorations (Oxford University Press 2017).

934

Giorgio Gaja, ‘General Principles of Law’, Max Planck Encyclopedia of Public International Law (Online Edition) (Oxford University Press 2013) para 2 <opil.ouplaw.com>.

935

Samantha Besson, ‘General Principles in International Law: Whose Principles?’ in Samantha Besson and Pascal Pichonnaz (eds), Les principes en droit européen / Principles in European Law (Schulthess 2011) 39, 48 ff; Filippo Fontanelli, ‘The Invocation of the Exception of Non-Performance: A Case-Study on the Role and Application of General Principles of International Law of Contractual Origin’ (2012) 1 Cambridge Journal of International and Comparative Law 119, 127.

936

Besson, ‘General Principles in International Law: Whose Principles?’ (n 935) 33. See also Gaja (n 934) para 7 ff; Wolfgang Weiss, ‘Allgemeine Rechtsgrundsätze des Völkerrechts’ (2001) 39 Archiv des Völkerrechts 394, 397 ff. See also art. 21(1)(b) and (c) icc Statute.

937

Besson, ‘General Principles in International Law: Whose Principles?’ (n 935) 33.

938

Crawford, Brownlie’s Principles of Public International Law (n 906) 37.

939

Besson, ‘General Principles in International Law: Whose Principles?’ (n 935) 28. See also d’Aspremont, ‘The Permanent Court of International Justice and Domestic Courts: A Variation in Roles’ (n 240) 230 f.

940

Besson, ‘General Principles in International Law: Whose Principles?’ (n 935) 36 f; Jain (n 73). For an example, see Judge Bruno Simma’s separate opinion in icj, case concerning Oil Platforms (Iran v. United States), judgment, merits, icj Reports 2003, 6 November 2003, 324, at 354, para 66 ff. I am grateful to León Castellanos-Jankiewicz for drawing my attention to this opinion.

941

pcij, case concerning the Factory at Chorzów, claim for indemnity, jurisdiction, pcij Series A No 9, 26 July 1927, 4, at 31, cited by Gaja (n 934) para 9.

942

d’Aspremont, ‘The Permanent Court of International Justice and Domestic Courts: A Variation in Roles’ (n 240) 230 f; Besson, ‘General Principles in International Law – Whose Principles?’ (n 935) 39; Sienho, ‘Article 38 of the icj Statute and Applicable Law: Selected Issues in Recent Cases’ (n 73) 488.

943

icty (Appeals Chamber), Prosecutor v. Duško Tadić, judgment, Case No it-94-1-a, 15 July 1999, para 225. See also icty (Trial Chamber ii), Prosecutor v. Zoran Kupreškić and Others, trial judgment, Case No it-95-16-t, 14 January 2000, para 680; icty (Trial Chamber ii), Prosecutor v. Anto Furundžija, judgment, Case No it-95-17/1-t, 10 December 1998, para 177.

944

See, with reference to icty (Trial Chamber i), Prosecutor v. Dražen Erdemović, sentencing judgment, Case No it-96-22-t, 29 November 1996, para 19: Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 289.

945

Besson, ‘General Principles in International Law: Whose Principles?’ (n 935) 60.

946

Pierre d’Argent, ‘Les principes généraux à la Cour internationale de Justice’ in Samantha Besson and Pascal Pichonnaz (eds), Les principes en droit européen / Principles in European Law (Schulthess 2011).

947

Nollkaemper notes that the icty has sometimes ‘endowed national decisions with an apparent quasi-independent authority that cannot be reduced to a constituent element of either customary international law or a general principle of (international) law’. Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 290.

948

Besson and Ammann (n 60) 69 f.

949

Eg ibid 80.

950

Besson, ‘Legal Philosophical Issues of International Adjudication: Getting Over the Amour Impossible Between International Law and International Adjudication’ (n 85). The expression was originally used by Ascensio (n 85).

951

Antonio Cassese highlights this tension between the law in the books and the law in practice by referring to the ‘wise’ versus the ‘wild approach’ of international judges towards ‘subsidiary means’: Antonio Cassese, ‘The Influence of the European Court of Human Rights on International Criminal Tribunals: Some Methodological Remarks’ in Morten Bergsmo (ed), Human Rights and Criminal Justice for the Downtrodden: Essays in Honour of Asbjørn Eide (Brill/Nijhoff 2003).

952

See however Aldo Zammit Borda, ‘A Formal Approach to Article 38(1)(d) of the icj Statute From the Perspective of the International Criminal Courts and Tribunals’ (2013) 24 European Journal of International Law 649; Zammit Borda (n 870).

953

See Zammit Borda (n 870) 68 f; Sienho (n 73) 491; Wolfrum (n 271) para 9.

954

Robert Jennings and Arthur Watts (eds), Oppenheim’s International Law, Vol I: Peace (9th edn, Longman 1996) 41.

955

La Forest (n 871) 98.

956

See Zammit Borda’s statement that ‘subsidiary means’ should ‘supplement’ a given interpretation: Zammit Borda (n 870) 70.

957

Pellet and Müller (n 187) 944 para 305.

958

Crawford, Brownlie’s Principles of Public International Law (n 906) 41; Wood (n 14) 12.

959

Jennings and Watts (n 954) 41.

960

Sienho Yee, ‘Report on the ilc Project on “Identification of Customary International Law”’ (2015) 14 Chinese Journal of International Law 375, 384.

961

See the definition of ‘auxiliary’ in <www.merriam-webster.com/dictionary/auxiliary>.

962

See also Pellet and Müller (n 187) 944 f para 306.

963

See ibid 953 para 323.

964

Hovell (n 871) 592; Jennings and Watts (n 954) 41 f; Higgins (n 365) 208. See also, for further references: Ammann, ‘The Court of Justice of the European Union and the Interpretation of International Legal Norms: To Be or Not to Be a “Domestic” Court?’ (n 140) 158, footnote 18.

965

Conclusion 13(2), ilc, ‘Draft Conclusions on Identification of Customary International Law, With Commentaries’ (n 891).

966

ilc Secretariat, ‘Identification of Customary International Law: The Role of Decisions of National Courts in the Case Law of International Courts and Tribunals of a Universal Character for the Purpose of the Determination of Customary International Law’ (n 185) 6 para 10; Zammit Borda (n 952) 652.

967

ilc Secretariat, ‘Identification of Customary International Law: The Role of Decisions of National Courts in the Case Law of International Courts and Tribunals of a Universal Character for the Purpose of the Determination of Customary International Law’ (n 185) 8 para 16.

968

See ibid 7 para 13.

969

See ibid 16 ff para 28 ff. The icty too refers to domestic rulings qua auxiliary means, although it gives prefers to cite international rulings if they are available. See ibid 25 ff para 41 ff. The ictr has occasionally used domestic rulings qua auxiliary means, see ibid 30 f para 47. On these two courts’ ‘wild approach’ to auxiliary means, see Cassese (n 951) 21 ff.

970

Besson and Ammann (n 60) 80.

971

Nollkaemper, ‘Decisions of National Courts as Sources of International Law: An Analysis of the Practice of the icty’ (n 182) 291.

972

Aldo Zammit Borda rejects the use of domestic rulings as a ‘direct souce’, as they would be relied upon in a ‘lax, uncritical’ way: Zammit Borda (n 870) 66. See also Cassese 21.

973

See ibid 82.

974

Jennings uses this expression with regard to international rulings: Jennings (n 40) 10, 12.

975

Zammit Borda (n 870) para 7.

976

Pellet and Müller (n 187) 947 para 312. The authors are quoting Jan Paulsson, ‘Report: International Arbitration and the Generation of Legal Norms: Treaty Arbitration and International Law’ in Albert Jan van den Berg (ed), International Arbitration 2006: Back to Basics (Kluwer Law International 2007) 881.

977

Grant Lamond, ‘Persuasive Authority in the Law’ (2010) 17 Harvard Review of Philosophy 16, 16.

978

See ibid 18. See also Joseph Raz, ‘Normativity: The Place of Reasoning’ (2015) 25 Philosophical Issues 144, 146.

979

Besson, ‘The Erga Omnes Effect of Judgments of the European Court of Human Rights – What’s in a Name?’ (n 137); Besson, ‘Legal Philosophical Issues of International Adjudication: Getting Over the Amour Impossible Between International Law and International Adjudication’ (n 85) 420, 422. See also von Bogdandy and Venzke (n 174); van de Kerchove (n 799) 698.

980

ilc Secretariat, ‘Identification of Customary International Law: The Role of Decisions of National Courts in the Case Law of International Courts and Tribunals of a Universal Character for the Purpose of the Determination of Customary International Law’ (n 185) 34 para 56; ilc, ‘Draft Conclusions on Identification of Customary International Law, With Commentaries’ (n 891) 149 para 3. See also Christopher Greenwood, ‘Unity and Diversity in International Law’ in Mads Andenas and Eirik Bjorge (eds), A Farewell to Fragmentation: Reassertion and Convergence in International Law (Cambridge University Press 2015) 51; Mendelson (n 73) 82; von Bogdandy and Venzke (n 174) 990 f.