Customary International Law Interpretation

doi:10.1017/9781009025416.023

22 - Customary International Law Interpretation

The Role of Domestic Courts

from Part V - Customary International Law in the Practice of Domestic Courts

Published online by Cambridge University Press: 05 May 2022

Edited by

Jörg Kammerhofer and

Panos Merkouris: Affiliation:
Rijksuniversiteit Groningen, The Netherlands
Jörg Kammerhofer: Affiliation:
University of Freiburg, Germany
Noora Arajärvi: Affiliation:
Hertie School of Governance, Berlin, Germany

Book contents

Summary

This chapter analyses a large dataset of domestic court decisions relevant to customary international law (CIL). It finds that domestic courts at times engage in CIL interpretation rather than mere ascertainment, even if they largely refrain from using that term. Domestic courts may interpret CIL autonomously, may defer to and validate international courts’ CIL interpretations, or interpret written documents, such as treaties, codifying CIL norms. Such practices bear out that domestic courts may consider some core CIL norms to be relatively stable and amenable to further refinement through interpretation. When interpreting CIL, domestic courts appear to resort mainly to systemic interpretation and interpretation on the basis of subsequent State practice. This reflects earlier findings by Panos Merkouris with respect to CIL interpretation by international courts. Domestic courts deciding cases on the basis of CIL may want to be more explicit regarding whether they engage in de novo CIL norm-identification or rather in the interpretation of pre-existing and stabilised customary norms. In case of interpretation, they may want to improve the methodological quality of their reasoning by pinpointing the canon of construction which they apply, and by relying on sufficient international (including foreign) legal practice.

Keywords

Domestic courts customary international law interpretation ascertainment

Type: Chapter
Information: The Theory, Practice, and Interpretation of Customary International Law , pp. 481 - 506

DOI: https://doi.org/10.1017/9781009025416.023 [Opens in a new window]

Publisher: Cambridge University Press

Print publication year: 2022
Creative Commons: This content is Open Access and distributed under the terms of the Creative Commons Attribution licence CC-BY-NC 4.0 https://creativecommons.org/cclicenses/

1 Introduction

The TRICI-Law project observes that ‘in the study of customary international law (CIL) there is a critical gap in understanding how CIL can be applied in individual cases once it has been formed’. The project then sets for itself the goal to uncover rules of interpretation of CIL. In the words of the project, if such rules were to exist, CIL need not be induced (ascertained) each and every time, by reference to state practice and opinio juris or asserted by judges.

This chapter attempts to narrow the gap in understanding how CIL is applied and interpreted by domestic courts. Domestic courts are important agents of international legal development,Footnote ¹ and they contribute to the entrenchment of the rule of international law, including CIL.Footnote ² Accordingly, a study of the interpretation of CIL cannot do without an analysis of domestic court practices.

The contribution opens with a critical reflection on the proposed doctrinal shift from mere CIL ascertainment to interpretation of more or less stabilised CIL norms (Section 2). As domestic courts tend to apply pre-existing CIL rather than ascertain CIL de novo,Footnote ³ the author sees a window of opportunity for CIL interpretation. He then goes on to ascertain whether domestic courts also use this window in practice. He does so by analysing a large data set of domestic court decisions (Section 3). The empirical analysis yields a number of ‘true positives’ which suggest that, in admittedly rare cases, domestic courts genuinely interpret relatively stable, pre-existing CIL norms, in particular in the area of international immunities. These courts appear to use methods of interpretation that reflect those used for treaty interpretation, notably systemic interpretation and interpretation taking into account subsequent practice.

2 From CIL Ascertainment to Interpretation

The quest for rules governing the interpretation of norms of international law other than treaty-based norms is not new. Reference can notably be made to the interpretation of the text of resolutions of the United Nations Security Council (UNSC).Footnote ⁴ The Advocate General advising the Dutch Supreme Court, for instance, recently opined that ‘while Article 31 VCLT did strictly speaking not apply to a resolution of the UN Security Council, its rule of interpretation can be considered as a rule of customary international law’.Footnote ⁵ The reasoning appears to be that, precisely because Article 31 of the Vienna Convention on the Law of Treaties (VCLT) is of a customary nature, it can also be applied to the interpretation of sources of international law other than treaty law, such as UNSC resolutions. If that is the case, nothing stands in the way of applying the rules of interpretation laid down in Article 31 VCLT to CIL as well.

This line of argumentation is not necessarily convincing, however. There may be little doubt regarding the customary character of Article 31 VCLT,Footnote ⁶ but that does not make the rules of interpretation laid down in that provision applicable to sources of international law other than the treaties which the VCLT is supposed to govern.Footnote ⁷ In fact, that the relevant rules of Article 31 VCLT are customary means, in the first place, that they can be applied to other treaties that are not governed by the VCLT, for example, because they predate the entry into force of the VCLT in 1980, because the state party to the relevant treaty has not ratified the VCLT, or because the treaty does not fall within the scope of the VCLT (for instance because it has been concluded in oral form, or between states and other subjects of international law, or between such other subjects inter se).Footnote ⁸ After all, Article 31(1) VCLT specifically stipulates that ‘[a] treaty shall be interpreted in good faith’.Footnote ⁹ If that rule has customary character, the parallel customary rule should also state ‘a treaty shall be interpreted in good faith’.

Nevertheless, this does not mean that Article 31 VCLT has no relevance for the interpretation of norms from other sources of international law. It may have such relevance, as a material source of inspiration, or via reasoning by analogy. In all likelihood, the VCLT rules of interpretation should not be transposed lock-stock-and-barrel to the interpretation of norms derived from other sources of international law, to paraphrase Arnold McNair’s warning in the International Court of Justice (ICJ) South West Africa advisory opinion not to simply import domestic law institutions into international law.Footnote ¹⁰ Rather, when considering transposition, one may have to bear in mind the special features of other sources of international law compared to treaty law. Thus, Sir Michael Wood has sympathy for interpreters’ reliance on Article 31 VCLT when interpreting UNSC resolutions, but, given the more political nature of this source of law, invites the interpreter to pay specific attention to the circumstances in which the resolution has been adopted as well as the context of the UN Charter.Footnote ¹¹

That the rules of interpretation devised for treaties can apply mutatis mutandis to UNSC resolutions is in any event understandable to the extent that a binding UNSC resolution is, just like a treaty, a written source of international law. Moreover, UNSC resolutions find their legal basis in a treaty (the UN Charter).Footnote ¹² It is less self-evident to apply Article 31 VCLT, with the necessary modifications or not, to the interpretation of CIL norms. Unlike a treaty or a UNSC resolution, CIL is an unwritten source of international law, and it does not, at least not formally, find its legal basis in a treaty. The material source of CIL may sometimes be a treaty, for example, because subsequent to the adoption of a treaty norm, state practice and opinio juris converge on the content of that norm, but at the end of the day, for its legal existence the customary norm is not dependent on the treaty norm.Footnote ¹³ Because CIL is an unwritten, flexible and protean source of international law, it does not easily lend itself to the transposition of rules of treaty interpretation. What is more, the question may arise whether rules of interpretation of customary law norms serve any purpose at all, as CIL is – at least potentially – in a state of constant flux. Interpretation of norms only makes sense if those norms have a stable existence. In the classic understanding of ascertainment and identification of norms of CIL, legal authorities (law-applying or law-ascertainment agencies) always have to revisit the very existence of customary norms de novo. Although unlikely, it is after all not impossible that customary norms change or form almost overnight (instant custom).Footnote ¹⁴

This also appears to follow from the very text of Article 38(1)(b) of the ICJ Statute, which provides that the ICJ (and courts more generally one may well posit) ‘shall apply’ … ‘international custom, as evidence of a general practice accepted as law’. Pursuant to this provision, courts apply a customary norm as soon as they have established its evidence-based existence, without any need for interpretation stricto sensu. This process may perhaps appear interpretative, in that judges interpret evidentiary materials placed before them with the aim of distilling customary norms from those materials. But such interpretation takes place only in an evidentiary rather than normative sense. Judges do not interpret previously crystallised norms by analogy with Article 31 VCLT; they simply ascertain the law. Thus, Merkouris observes that judges do ‘not interpret State practice, they evaluate it, they examine its gravity for the purpose of determining the existence or not of CIL’, whereas ‘interpretation of CIL requires an already existing CIL rule’.Footnote ¹⁵

This process of CIL ascertainment or identification has been the subject of many studies, most recently by the International Law Commission (ILC).Footnote ¹⁶ In a previous publication with a co-author, this author systematised and categorised the variegated CIL ascertainment techniques used by domestic courts.Footnote ¹⁷ Triggered by Stefan Talmon’s earlier finding that, ‘when determining the rules of customary international law, the ICJ does not use one single methodology but, instead, uses a mixture of induction, deduction and assertion’,Footnote ¹⁸ it was examined whether similar processes could be witnessed in domestic courts. An analysis of a large number of recent domestic court cases bore out that this is indeed the case. Domestic courts do not normally identify CIL norms on the basis of the textbook method of ascertaining a general practice accepted as law. Rather, they tend to outsource the determination of custom to treaties, non-binding documents, doctrine or international judicial practice. Sometimes, these courts simply assert, without citing persuasive practice, the existence of a customary norm.

While, in principle, ‘other authorities’ only have evidentiary value that should be weighted with other materials which more inductively evidence (or not) the existence of a particular customary norm, one cannot escape the impression that domestic courts are simply giving effect to, or applying pre-existing customary norms, that is, norms which have been identified earlier. But if that is true, there is in principle room for the development of rules of interpretation. As Merkouris observed: ‘[O]nce CIL has been identified as having been formed, its continued manifestation and application in a particular case will be dependent on the deductive process of interpretation. In this manner, interpretation focuses on how the rule is to be understood and applied after the rule has come into existence and for its duration.’Footnote ¹⁹ If domestic courts are in fact interpreting customary norms when applying them in given cases, our earlier publication’s lament that domestic courts failed to engage in a serious CIL ascertainment process (which includes parsing all available materials),Footnote ²⁰ loses some of its force. Indeed, assuming that customary norms existentially stabilise at one point, after which they are simply interpreted, there is no need for an elaborate process of identifying a customary norm de novo. Instead, courts may satisfy themselves with reaffirming the existence of the norm – presumably established by other law-ascertainment agencies at an earlier stage without subsequently being challenged – and instead concentrate on how to interpret the norm in a manner similar to how treaty interpretation takes place. Specific CIL rules of interpretation that are autonomous from the VCLT rules of interpretation can, in principle, develop via the regular customary process, through concurrent state practice and opinio juris.Footnote ²¹ Merkouris has argued that such rules already exist, and that they themselves are amenable to interpretation.Footnote ²²

3 The Practice of Domestic Courts Interpreting CIL

The author’s earlier research on how domestic courts found and applied customary norms was conducted through the lens of ascertainment. The current contribution, revisits relevant court decisions with a view to understanding more in-depth how domestic courts engage in CIL interpretation.

Oxford University Press’s database International Law in Domestic Courts (ILDC) was used as the main resource to find relevant domestic court decisions. ‘Interpretation’ was used as the search term, combined with the generic subject ‘Sources, foundations and principles of international law’. The headnote of the search results subsequently indicates whether CIL was relevant to the domestic court decision.Footnote ²³ Also, ILDC marks the search term – in this case ‘interpretation’ – in the summary and text of the decision, which greatly facilitated the research.Footnote ²⁴ Methodologically, a discourse analysis of written texts (judgments) was carried out;Footnote ²⁵ the research analysed to what extent domestic courts explicitly used the term ‘interpretation’ when applying CIL.Footnote ²⁶ Such an analysis has its limitations in that it may discount practices of courts implicitly interpreting customary norms. Accordingly, it also included references to interpretation by the ILDC commentators directly commenting on the judgments. However, the emphasis does not lie on what courts may have meant when applying customary norms, but primarily on what they did in fact: did they consciously consider customary norms to be amenable to interpretation?

The search yielded a number of domestic court decisions which featured both ‘customary international law’ and ‘interpretation’. However, not all of these results pertain to the interpretation of CIL norms proper. Such results are ‘false positives’.Footnote ²⁷ A first category of false positives comprises those decisions in which domestic courts erroneously use the term ‘interpretation’, when they in fact meant something else, in particular ascertainment. A second category of false positive comprises those decisions in which courts do engage in interpretation, but not of CIL, but rather of domestic (statutory) law, although in light of CIL. These two categories of false positives are briefly discussed in Section 3.1. Subsequently, Section 3.2 proceeds to the core analysis of true positives, that is, decisions in which courts genuinely interpret CIL norms.

3.1 False Positives

A number of domestic court decisions in which courts profess to interpret CIL are in fact examples of CIL ascertainment. These cases are false positives as they pertain to the identification of the very existence of a customary norm rather than its subsequent interpretation. For example, in the US Court of Appeals (Second Circuit) judgment in Kiobel, Leval, J., concurring, criticises the majority’s holding that corporate liability does not exist under CIL,Footnote ²⁸ on the following grounds: ‘The majority’s interpretation of international law, which accords to corporations a free pass to act in contravention of international law’s norms, conflicts with the humanitarian objectives of that body of law.’Footnote ²⁹ What the majority in fact did in Kiobel was ascertaining the very existence of a customary norm providing for liability of corporations for violations of international law, rather than ‘interpreting (the body of) international law’. Another example is the following characterisation by the US Court of Appeals (11th Circuit) of the difficulties of determining offences that violate CIL under the Offences Clause of the US Constitution (such as offences of drug trafficking):

The determination of what offenses violate customary international law … is no simple task. Customary international law is discerned from myriad decisions made in numerous and varied international and domestic arenas. Furthermore, the relevant evidence of customary international law is widely dispersed and generally unfamiliar to lawyers and judges. These difficulties are compounded by the fact that customary international law – as the term itself implies – is created by the general customs and practices of nations and therefore does not stem from any single, definitive, readily-identifiable source. All of these characteristics give the body of customary international law a soft indeterminate character that is subject to creative interpretation.Footnote ³⁰

Here, the court refers to evidentiary interpretation, that is, the process of parsing state practice with a view to ascertaining CIL. It does not refer to the interpretation of customary norms that have already come into existence.

A final example is the US trial court judgment in Talisman, where the court held that ‘interpretations of [customary] international law [the law of nations] of the Supreme Court and Second Circuit are binding upon this Court’.Footnote ³¹ This case also concerned the question of whether corporations may be liable for international law violations, which, as pointed out above, is a matter of ascertainment rather than interpretation of international law. This lower court simply wanted to say that, on the basis of stare decisis, it has little agency in ascertaining CIL.Footnote ³² Of course, this need not totally exclude its interpretation of this law subsequent to its ascertainment – an issue which the court however did not address.

The search also yielded a relatively large number of potentially relevant cases that pertained to statutory interpretation in light of CIL. These cases are false positives as well, in that they are instances of ‘consistent interpretation’, that is, interpretation of domestic law in light of international law,Footnote ³³ rather than interpretation of CIL proper. For instance, the Supreme Court of Appeal of South Africa held that ‘[w]hen interpreting legislation, the courts had to prefer a reasonable interpretation that was consistent with international law [including CIL] over any alternative inconsistent interpretation’.Footnote ³⁴ Another example is the Italian Supreme Court’s interpretation of a provision in the Italian criminal code in light of CIL on the prevention of terrorism.Footnote ³⁵ Also included in this category are a large number of immunity cases from Anglo-Saxon jurisdictions (such as the USA, UK, Canada), which have adopted specific immunity legislation, and whose courts go on to interpret such legislation in light of customary immunity rules.Footnote ³⁶ In the end, however, all these decisions, while interesting in their own right, do not interpret customary international law, but rather statutory law, unless it happens that, when interpreting statutory law, they also explicitly interpret rather than merely apply CIL.

Somewhere on a continuum between false and true positives are instances of ‘reverse’ consistent interpretation. Reverse consistent interpretation can be defined as interpretation of CIL in light of domestic law, meaning that in case of various possible interpretations of a norm, the interpretation that is most consistent with domestic law should be chosen. An Israeli judgment can serve as an example. In a case on the scope of state immunity from jurisdiction, the Supreme Court of Israel held that ‘[a]mong various possible alternatives offered by customary international law, an Israeli court should have chosen the alternative most consistent with the basic values of Israeli law, which, in the present context, favoured the restriction of state immunity’.Footnote ³⁷ While the Israeli court appears to be interpreting CIL, using the method of systemic interpretation, it does so in a very insulated and parochial manner, by paying heed to the values of the domestic legal system rather than to ‘the relevant rules of international law’.Footnote ³⁸ Following Odile Ammann, such an interpretative approach can be considered as disregarding or misapplying the interpretative methods of international law, and thus lacking quality and legality.Footnote ³⁹ Interpretation requires international interaction,Footnote ⁴⁰ that is, paying attention to how other states apply and interpret customary norms. Accordingly, instances of reverse consistent interpretation can largely be considered as false positives.

3.2 True Positives

The research did not just yield decisions in which domestic courts did not engage in CIL interpretation proper. In some cases, domestic courts appear to truly interpret CIL norms. These are the ‘true positives’ in which we are interested. They demonstrate that domestic courts assume that they can interpret CIL norms,Footnote ⁴¹ even if they have not given much thought to the doctrinal underpinnings or normative consequences of CIL interpretation.

Most relevant domestic court decisions relate to immunities. This is not surprising as (1) immunities are normally invoked before domestic courts and (2) the law of immunities, in particular the immunities of states and their officials, is one of the few fields of international law that is largely governed by CIL.Footnote ⁴² As pointed out above, in Anglo-Saxon jurisdictions, international immunities tend to be laid down in statutes, as result of which statutory law – possibly interpreted in light of CIL – will be applied. However, in other jurisdictions, for example on the European continent, immunities are directly derived from (customary) international law, possibly via a renvoi provision in domestic legislation.Footnote ⁴³

For analytical and pedagogical purposes, these decisions are clustered into three theoretical categories. These categories have been generated inductively through coding, conceptualising and analysing the available data (the court decisions referencing interpretation). In social science, such an approach would be termed ‘grounded theory research’.Footnote ⁴⁴ As the coding exercise is carried out by human beings, the data may obviously feed into different categories.Footnote ⁴⁵ However, the generic categories offered here may have particular expository power in that they are also transferable to CIL interpretation by law-interpreting agencies other than domestic courts, for example international courts. They allow us to zoom out of the particular context in which domestic courts apply and interpret law, and to reflect at a more abstract level on the practice of CIL interpretation.

The following analytical categories will be successively discussed: (3.2.1) autonomous CIL interpretation, (3.2.2) deference to CIL interpretation by other (international) courts and (3.2.3) interpreting CIL norms laid down in authoritative (written) documents. In the discussion, particular attention is paid to the method of interpretation applied by the court.

3.2.1 Autonomous CIL Interpretation

The research yielded a number of decisions in which domestic courts appeared to interpret CIL relatively autonomously, that is, without (explicitly) taking their cue from international courts’ interpretations, or from written documents purportedly codifying CIL. Most of these decisions pertain to the immunity ratione materiae of state officials from foreign criminal jurisdiction, which has not been codified, at least not until recently,Footnote ⁴⁶ and regarding which international courts have given little to no guidance. A Swiss, US and Italian case were considered to be relevant.

In A v. Swiss Federal Public Prosecutor, the Swiss Federal Criminal Court interpreted the customary norms on state official immunity ratione materiae (functional immunity) as follows, in a case concerning the claimed immunity of a former defence minister of a foreign state regarding a charge of war crime:

It remained to be decided whether A’s residual immunity ratione materiae covered acts performed while in office, and whether it trumped the necessity of establishing his responsibility for alleged grave human rights violations. In light of … developments, it was not clear that this immunity should prevail, as serious crimes against humanity, including torture, were prohibited by customary international law. The Swiss legislature’s commitment to repressing ius cogens violations was an additional reason for denying A immunity ratione materiae, as it would be contradictory to express such a commitment while giving a broad interpretation to this immunity.Footnote ⁴⁷

Arguably, the Swiss court assumed that a state official’s immunity ratione materiae for official acts had already crystallised as a customary norm and thus had a relatively stable existence.Footnote ⁴⁸ What mattered now, was how to understand and apply the norm in respect of jus cogens violations. This is an interpretative exercise that mirrors the interpretative rule enshrined in Article 31(3)(c) VCLT, pursuant to which ‘[t]here shall be taken into account, together with the context … any relevant rules of international law applicable in the relations between the parties’.

A practice of interpreting functional immunity in respect of jus cogens violations can also be gleaned from the judgment of the US Court of Appeals for the Fourth Circuit in Yousuf v. Samantar, which concerned the same question of whether a high-ranking government official was immune from suit under head-of-state immunity or foreign official immunity for jus cogens violations, even if the acts had been performed in the defendant’s official capacity.Footnote ⁴⁹ The case had been remanded by the US Supreme Court, which had held that the Foreign Sovereign Immunities Act did not govern a claim of immunity by a foreign official.Footnote ⁵⁰ On remand, the Court of Appeals held that the common law, which included CIL, governed such a claim,Footnote ⁵¹ and it went on to (arguably) interpret functional immunity, holding that ‘[t]here has been an increasing trend in international law to abrogate foreign official immunity for individuals who commit acts, otherwise attributable to the State, that violate jus cogens norms – i.e., they commit international crimes or human rights violations’.Footnote ⁵² Admittedly, the court itself did not use the term interpretation, but the ILDC commentator conspicuously did, not only in the analysis of the judgment, but also in the Held section which is supposed to simply restate the court’s reasoning.

There is obviously a fine distinction with law ascertainment here, as it could as well be argued that whether immunity ratione materiae extends to international crimes is itself amenable to customary law formation: can sufficient state practice be identified to buttress the crystallisation of a customary law exception to the immunity ratione materiae of state officials?Footnote ⁵³ However, both courts embraced a deductive approachFootnote ⁵⁴ which emphasises the relationship of immunity with jus cogens norms. Such an approach can be termed ‘interpretative’, as it gives meaning to an established customary norm in the specific milieu of international crimes. The fact that a court may also cite other state practice (other domestic court decisions)Footnote ⁵⁵ does not necessarily render the process one of customary law ascertainment, as such practice may well qualify as subsequent practice in the application of the customary norm which establishes the agreement of states regarding its interpretation, to paraphrase Article 31(3)(b) VCLT. Specifically regarding the purported immunity ‘exception’ for jus cogens violations, the systemic integration-based technique of interpretation may also be of particular relevance, that is, the interpretation of a customary norm in light of ‘any relevant rules of international law applicable in the relations between the [states]’, to paraphrase Article 31(3)(c) VCLT; jus cogens norms qualify as such rules.Footnote ⁵⁶

The fine line between law ascertainment and interpretation is also apparent in another functional immunity case, Abu Omar, before the Italian Court of Cassation. In this case, which pertained to the question of whether, under CIL, state officials who had participated in an extraordinary rendition operation enjoyed functional immunity from the criminal jurisdiction of a foreign state, the court decided as follows:

The problem … consists of checking whether there effectively exists a customary law regulation under international law that also guarantees criminal immunity to the individual-entity of a sovereign state, even when it does not involve Diplomatic and/or Consular officials and high appointments of state.

On this point, jurisprudence is divided, because alongside those authorities that recognise the existence of a customary law regulation of this kind, there are others that recognise this only in respect of the activities authorised by the foreign country where these take place, while there are still others that maintain that the benefit of immunity is recognised according to specific regulations only to certain categories of entities in exercising the functions that are typical of their office.

This Court believes that this last interpretation is the more correct one, because it takes into account the developments in international relations, which as already stated, the Nato [London] Convention [Agreement between the Parties to the North Atlantic Treaty regarding the Status of their Forces] and the [Vienna Convention on Consular Relations] are valid examples.Footnote ⁵⁷

At first sight, in this case, the Italian court appears to ascertain the very existence of a customary norm on functional immunity (‘checking whether there effectively exists a customary law regulation’). However, the court’s use of the term ‘interpretation’ is not necessarily misguided, as what the court may actually be doing is to interpret the scope of functional immunity, without casting doubt on the principled customary existence of functional immunity (the ‘core norm’). The judgment could be read as affirming the principled existence of customary functional immunity, while denying its blanket application to all categories of state entities exercising official functions. To reach the conclusion that functional immunity under customary law ‘only’ applies to certain categories, the court appears to have recourse to contextual interpretation, when it states that it ‘takes into account the developments in international relations’.

Finally, there is a decision by the Belgian Court of Cassation with respect to immunity from execution, which is particularly relevant from a conceptual perspective. In this decision, the court held as follows:

Il ne résulte pas de [l’article 38, § 1er, b), du Statut de la Cour internationale de Justice] que le juge étatique qui identifie et interprète une règle coutumière internationale est tenu de constater, dans sa décision, l’existence d’une pratique générale, admise par une majorité des États, qui soit à l’origine de cette règle coutumière.Footnote ⁵⁸

What the court states here is that domestic courts identifying and interpreting a CIL norm are not required to establish the existence of a general practice accepted by a majority of states which is at the origin of the CIL norm. As the court uses the terms ‘identifying’ and ‘interpreting’, it is apparent that the court is not conflating law ascertainment and law interpretation. Arguably, the court uses the term ‘interpretation’ in response to the applicant’s subsidiary argument that the lower court:

[N]e justifie pas légalement sa décision en rendant applicable aux comptes d’ambassade la règle ne impediatur legatio, à supposer celle-ci établie, sans constater d’abord qu’une majorité des États admet que la règle ne impediatur legatio consacre également une immunité d’exécution diplomatique autonome des comptes d’ambassade (violation de la règle coutumière internationale ne impediatur legatio).Footnote ⁵⁹

Thus, the applicant assumes, arguendo, that the CIL norm ne impediatur legatio has already crystallised,Footnote ⁶⁰ and then proceeds to argue that the majority of states still need to accept that this norm also provides for autonomous diplomatic immunity from execution of embassy bank accounts.Footnote ⁶¹ The Court of Cassation rejects this argument. While in the context of law identification, this holding may possibly be problematic,Footnote ⁶² it is far less so in the context of law interpretation insofar as the core CIL norm has already crystallised and no proof of existence needs to be adduced. The Court of Cassation ultimately does not state what rules govern the interpretation of CIL norms (the principle of ne impediatur legatio in particular), nor does the lower court.Footnote ⁶³

3.2.2 Deference to CIL Interpretation by International Courts

In Conclusion 13(1) of its draft conclusions on identification of CIL, the ILC states that ‘[d]ecisions of international courts and tribunals, in particular of the International Court of Justice, concerning the existence and content of rules of customary international law are a subsidiary means for the determination of such rules’.Footnote ⁶⁴ And indeed, domestic courts tend to look to international courts for guidance when ascertaining international law.Footnote ⁶⁵ However, they may also refer and defer to international courts which have interpreted CIL. Such domestic court decisions are relevant in that they confirm the methodological validity of interpreting CIL.

Three decisions with respect to the immunity of states, the scope of which the ICJ clarified in Jurisdictional Immunities of the State,Footnote ⁶⁶ stand out. In Simoncioni, the Italian Constitutional Court cited the ‘interpretation by the ICJ of the customary rule on state immunity for acts iure imperii’ in Jurisdictional Immunities of the State.Footnote ⁶⁷ By the same token, in Alessi, the Florence Court of First Instance held that the Italian court is not permitted ‘an interpretation of the binding, inescapable validity of the jus cogens rules of international law, the area in which the International Court of Justice has absolute and exclusive jurisdiction’.Footnote ⁶⁸ In the context of state immunity from execution, a commentator commenting on a decision of the German Federal Court of Justice somewhat similarly pointed out that the distinction between state property used for sovereign purposes and property not so used ‘corresponded to the interpretation of customary international law on immunity from enforcement given by the International Court of Justice (‘ICJ’) in Jurisdictional Immunities’.Footnote ⁶⁹

That the ICJ interpreted customary law in Jurisdictional Immunities of the State is itself an interpretation by domestic courts, for that matter. Indeed, in Jurisdictional Immunities of the State the ICJ did not explicitly use the term ‘interpretation’ in the context of immunities under CIL. Still, the judgment contains indications that the ICJ did actually interpret rather than ascertain CIL on immunities, in line with how the aforementioned domestic courts construed the ICJ’s judgment. First, with respect to immunity from jurisdiction, the ICJ stated in respect of Article 12 of the UN Convention on Jurisdictional Immunities that ‘[n]o state questioned this interpretation’,Footnote ⁷⁰ that is, the interpretation that military activities are not covered by the territorial tort exception. While it may appear that the ICJ interpreted the convention and thus simply applied rules of treaty interpretation – in this case having recourse to the travaux préparatoires of the convention per Article 32 VCLT – it bears emphasis that the convention had not yet entered into force. The territorial tort exception being of customary law character,Footnote ⁷¹ the ICJ may instead have interpreted the CIL equivalent of the conventional exception. The stabilised ‘core’ customary norm is that immunity in principle does not extend to territorial torts, whereas interpretation of that norm may yield the identification of the limited circumstances in which immunity does extend to territorial torts. Second, with respect to state immunity from execution, the ICJ may have used the term ‘find’,Footnote ⁷² which may suggest ascertainment rather than interpretation of the law,Footnote ⁷³ but it is of note that ‘find’ has other meanings too. The most relevant are ‘to discover’ and ‘to determine and make a statement about’,Footnote ⁷⁴ the latter approximating the meaning of ‘to interpret’ as ‘to conceive in the light of individual belief, judgment, or circumstance’.Footnote ⁷⁵ Accordingly, what the ICJ possibly did was to interpret a core customary norm on state immunity from execution on the basis of ‘subsequent practice in the application of the [customary norm] which establishes the agreement of [states] regarding its interpretation’, to paraphrase Article 31(3)(b) VCLT. Besides, the customary norm on state immunity could also be interpreted in light of international human rights law, in particular creditors’ rights to a remedy and to property.Footnote ⁷⁶ Such an interpretation would give effect to the CIL equivalent of Article 31(3)(c) VCLT. Arguably, the relevant core customary norm is that state immunity from execution is not absolute, but relative. Under what precise circumstances state immunity does not apply will then be amenable to interpretation.Footnote ⁷⁷

3.2.3 Interpreting CIL Norms Laid Down in Authoritative (Written) Documents

A third category is made up of those decisions that indirectly interpret CIL norms by interpreting the written documents in which they have been laid down. Insofar as CIL is laid down in an authoritative written text, courts will be more likely to have recourse to customary law interpretation than to customary law ascertainment, as supposedly the norm has already crystallised, black-on-white. It is the very codification of customary law which gives this body of law a more stable existence and shifts the focus to subsequent interpretation. Methodologically speaking, reliance on codification treaties to understand the meaning of CIL rules is a form of systemic interpretation mirroring the interpretative rule laid down in Article 31(3)(c) VCLT, the written text being a ‘relevant rule of international law’.Footnote ⁷⁸

The most obvious written documents serving such a purpose are treaties. Thus, it is no surprise that the ICJ relied on, and arguably interpreted Article 12 of the UN Convention on Jurisdictional Immunities as CIL, as discussed in Section 3.2.2. Another example is offered by US courts’ reliance on the UN Convention on the Law of the Sea (UNCLOS), to which the US is not a party, for purposes of applying parallel CIL of the sea with the same content.Footnote ⁷⁹ The application of such CIL also has an interpretative dimension, as is borne out by the Sea Shepherd case. In this case, the US Court of Appeals for the Ninth Circuit interpreted the ‘private ends’ requirement of piracy by taking the UNCLOS definition of piracy (Article 101 UNCLOS) as the starting point for its investigation of whether ‘private ends’ include those pursued on personal, moral or philosophical grounds, such as the NGO Sea Shepherd’s professed environmental goals.Footnote ⁸⁰ The court held as follows: ‘Belgian courts, perhaps the only ones to have previously considered the issue, have held that environmental activism qualifies as a private end. … This interpretation is “entitled to considerable weight”’.Footnote ⁸¹ What the court was in fact doing was to interpret the ‘private ends’ variant of the CIL definition of piracy, which just happens to be codified in UNCLOS. The interpretative rule applied by the court was arguably the one based on subsequent practice, echoing Article 31(3)(b) VCLT.Footnote ⁸²

The shift from ascertainment to interpretation, facilitated by CIL having been laid down in a written document, may not be limited to situations of CIL norms codified in a treaty. It may also extend to situations of such norms being derived from authoritative, although non-binding written documents. An example of a court apparently interpreting CIL laid down in such a document is the Haifa District Court (Israel), which held that the non-binding San Remo Manual on International Law applicable to Armed Conflicts at Sea (1990)Footnote ⁸³ was recognised as reflecting CIL, and thus that the authority for confiscating a vessel, at issue in the case, derived from CIL.Footnote ⁸⁴ The court then proceeded to find that most states required legal adjudication for an act of confiscating a vessel and also required a speedy court procedure,Footnote ⁸⁵ thereby apparently interpreting the provisions of the San Remo Manual on prize law (which do not set forth a court procedure) by resorting to subsequent practice. Admittedly, the court itself did not use the term interpretation, but the ILDC commentator did, observing, in addition, that ‘any maritime court would have to address the potential impact of human rights law on the interpretation of the right to capture blockade-runners under traditional prize law’ (thus favouring systemic interpretation taking into account other norms of international law).Footnote ⁸⁶ The Israeli Court decision suggests that law interpreters may consider CIL norms that have been laid down in authoritative non-binding documents to lead a relatively stable existence, and thus to be amenable to interpretation.Footnote ⁸⁷

4 Concluding Observations

By and large, domestic courts, just like international courts, hew to the fiction that they find, identify or ascertain CIL. Earlier research has demonstrated that domestic courts have only limited agency in identifying CIL.Footnote ⁸⁸ Instead, they tend to simply apply pre-existing CIL. However, when domestic courts apply such CIL, they may also interpret and develop CIL, as any application of law, almost out of necessity, also involves a measure of interpretation and legal development.Footnote ⁸⁹ This contribution supports the TRICI project’s methodological premise that CIL norms, just like treaty norms, can be interpreted. Interpretation will notably take place after a ‘core’ CIL norm has crystallised and stabilised, after which the penumbra of that rule – its precise scope, its exceptions – are amenable to mechanisms of interpretation.

This chapter has analysed a large dataset of domestic court decisions relevant to CIL, and found that, indeed, domestic courts at times engage in CIL interpretation, even if they largely refrain from using that term. Domestic courts may interpret CIL autonomously, may defer to and validate international courts’ CIL interpretations, or they interpret written documents, such as treaties, codifying CIL norms. Such practices bear out that domestic courts may consider some core CIL norms to be relatively stable and amenable to further refinement through interpretation.

When interpreting CIL, domestic courts appear to resort mainly to systemic interpretation and interpretation on the basis of subsequent state practice. This reflects earlier findings by Panos Merkouris with respect to CIL interpretation by international courts.Footnote ⁹⁰ In particular, domestic courts apply by analogy the canons of construction laid down in Article 31(3)(b) VCLT (‘any subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation’), and Article 31(3)(c) (‘any relevant rules of international law applicable in the relations between the parties’). The analysis of state practice under the CIL equivalent of Article 31(3)(b) VCLT tends to be cursory, however. As Odile Ammann has pointed out, mainly in respect of CIL ascertainment, domestic courts tend to refer to their own practice or the practice of their own state, a process which she characterises as self-referentiality and circularity.Footnote ⁹¹ Cast in terms of interpretation, such a process may take the form of ‘reverse consistent interpretation’: domestic courts may choose this interpretation of a CIL norm which is mostly in line with domestic law and practice.Footnote ⁹²

In future cases, domestic courts deciding cases on the basis of CIL may in any event want to be more explicit regarding whether they engage in de novo CIL norm-identification or rather in the interpretation of pre-existing and stabilised customary norms. In case of interpretation, they may want to improve the methodological quality of their reasoning by pinpointing the canon of construction which they apply (e.g., systemic interpretation; interpretation on the basis of subsequent practice). Finally, in the case of both CIL identification and interpretation, they should make sure that they rely on sufficient international (including foreign) legal practice, in keeping with the methodological requirements of CIL identification and interpretation.

Footnotes

¹ A Tzanakopoulos & CJ Tams, ‘Introduction: Domestic Courts as Agents of Development of International Law’ (2013) 26 LJIL 531.

² A Nollkaemper, National Courts and the International Rule of Law (Oxford University Press 2012).

³ CMJ Ryngaert & DW Hora Siccama, ‘Ascertaining Customary International Law: An Inquiry into the Methods Used by Domestic Courts’ (2018) 65 NILR 1.

⁴ For example State of the Netherlands v [respondent] et al (14 December 2012) Supreme Court of the Netherlands, AG Advisory Opinion, 11/03521 [3.7.2]; in a most recent case decided by the Dutch Supreme Court the Advocate General (AG),who advises the Court also applied Article 31(1) VCLT to the term ‘asset freeze’ as it featured in a UN Security Council resolution (Libya sanctions), emphasising the ordinary meaning of the notion of ‘asset freeze’ Palladyne International Asset Management BV v Upper Brook (I) Limited (12 October 2018) Supreme Court of the Netherlands, AG Advisory Opinion, 17/03964 [3.13]; while the court itself did not cite Article 31(1) VCLT and reached another conclusion than the AG regarding the meaning of an asset freeze, it drew attention to the objective of the resolution, Palladyne International Asset Management BV v Upper Brook (I) Limited (18 January 2019) Supreme Court of the Netherlands, 17/03964 [3.6.3] (‘Ook zou een beperkte uitleg afbreuk kunnen doen aan het doel van de resoluties om de tegoeden ten goede te laten komen aan de bevolking van Libië.’). Thus, the court implicitly applied Article 31(1) VCLT which counsels both textual and teleological interpretation (‘A treaty shall be interpreted in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose.’).

⁵ Palladyne International Asset Management BV v Upper Brook (I) Limited, AG Advisory Opinion [3.5] (author’s translation); State of the Netherlands v [respondent] et al fn 23 (‘De uitlegregels van verdragen gelden ook voor besluiten van internationale organisaties, hoewel het WVV daarop strikt genomen geen betrekking heeft. Art. 31 WVV kan echter worden gezien als een regel van internationaal gewoonterecht’); see A Orakhelashvili, ‘The Acts of the Security Council: Meaning and Standards of Review’ (2007) 11 UNYB 149, 153, 157; MC Wood, ‘The Interpretation of Security Council Resolutions’ (1998) 2 UNYB 73.

⁶ See O Dörr, ‘Article 31. General Rule of Interpretation’ in O Dörr & K Schmalenbach (eds), Vienna Convention on the Law of Treaties: A Commentary (Springer 2012) 521 [6] with references to relevant case law of the ICJ and other international dispute-settlement bodies.

⁷ Similar confusion may perhaps surround the binding character of customary international norms for subjects other than states, such as international organisations or other non-state actors. The argument would then go that, because a particular norm is of a CIL character, that law is necessarily binding on other subjects of international law, or at the very least on intergovernmental organisations (which happen to typically consist of states). See regarding international organisations N Blokker, ‘International Organizations and Customary International Law: Is the International Law Commission Taking International Organizations Seriously?’ (2017) 14(1) IOLR 1 [3] (submitting that ‘in the areas in which powers have been given to international organizations, it is increasingly recognized that these organizations are bound by the relevant rules of customary international law that are applicable in these areas’); see regarding non-state armed (opposition) groups: S Sivakumaran, ‘Binding Armed Opposition Groups’ (2006) 55(2) ICLQ 369 (discussing the explanation of the binding character of international humanitarian law (IHL) for non-state armed groups in the context of IHL being, at least in part, customary in nature, although in the end considering the state’s ability to legislate on behalf of all its individuals to be the best explanation).

⁸ Article 2(a) VCLT (‘“treaty” means an international agreement concluded between States in written form’). Note that there is a 1986 Vienna Convention on the Law of Treaties between States and International Organizations or Between International Organizations (not yet in force), which in Articles 31–33 restates the corresponding articles of the 1969 VCLT.

⁹ Emphasis added.

¹⁰ International Status of South West Africa (Advisory Opinion) [1950] ICJ Rep 146, Separate Opinion of Judge McNair, 148.

¹¹ MC Wood, ‘The Interpretation of Security Council Resolutions, Revisited’ (2017) 20 UNYB 1.

¹² Compare Charter of the United Nations (adopted 26 June 1945, entered into force 24 October 1945) 1 UNTS XVI 40, art 25 UN Charter (‘The Members of the United Nations agree to accept and carry out the decisions of the Security Council in accordance with the present Charter’). In fact, in the context of Article 103 of the UN Charter (‘In the event of a conflict between the obligations of the Members of the United Nations under the present Charter and their obligations under any other international agreement, their obligations under the present Charter shall prevail’), legal obligations under the charter are considered as largely synonymous with legal obligations under UNSC resolutions; see for example S Kitharidis, ‘The Power of Article 103 of the UN Charter on Treaty Obligations’ (2016) 20 IP 111.

¹³ For instance, when the treaty norm disappears, for example because the treaty is terminated, the customary norm can survive. Admittedly, a relatively stronger argument can be made for reliance on VCLT rules of treaty interpretation, or any rules of interpretation for that matter, in case of parallel existence of a customary norm with the same content, and in particular in case of that customary norm having been developed on the basis of the treaty norm: in case of parallelism, the customary norm is likely to be more stable, as it mirrors the treaty norm. See in this respect also the ICJ’s reference to interpretation of CIL in Military and Paramilitary Activities in and against Nicaragua (Nicaragua v USA) (Merits) [1949] ICJ Rep 14 [178] (‘Rules which are identical in treaty law and in customary international law are also distinguishable by reference to the methods of interpretation and application’).

¹⁴ See on instant custom regarding the use of force for example B Langille, ‘It’s “Instant Custom”: How the Bush Doctrine Became Law after the Terrorist Attacks of September 11, 2001’ (2003) 26 BC Int’l & Comp L Rev 145, 145–56.

¹⁵ P Merkouris, ‘Interpreting the Customary Rules on Interpretation’ (2017) 19 Int CL Rev 126, 138.

¹⁶ ILC, ‘Draft conclusions on identification of customary international law, with commentaries’ (30 April–1 June and 2 July–10 August 2018) UN Doc A/73/10, reproduced in [2018/II – Part Two] YBILC.

¹⁷ Ryngaert & Hora Siccama (Footnote n 3).

¹⁸ S Talmon, ‘Determining Customary International Law: the ICJ’s Methodology between Induction, Deduction and Assertion’ (2015) 26 EJIL 417.

¹⁹ Merkouris (Footnote n 15) 136; see also P Merkouris, Article 31(3)(c) VCLT and the Principle of Systemic Integration: Normative Shadows in Plato’s Cave (Brill 2015) 241–42

[A] rule of customary international law, once identified by an international court or tribunal, does not cease to exist. When the same or a different judicial body attempts to apply the same rule in a different case, it usually does not go on about re-establishing that the rule in question is customary international law. It considers it as a given, but this does not imply that it can immediately apply it either. In this context, between the identification of a customary rule and its application at a later date and in a different case there is an intermediate stage; that of interpretation of the rule by the later court or tribunal.

²⁰ Ryngaert & Hora Siccama (Footnote n 3) 23.

²¹ See Merkouris (Footnote n 15) 141 (‘[T]here are rules that guide the process of interpretation of CIL, although these will be, by virtue of the nature of CIL, different than those of treaties’), also citing North Sea Continental Shelf cases (Federal Republic of Germany v Denmark; Federal Republic of Germany v Netherlands) (Judgment) [1969] ICJ Rep 3, Dissenting Opinion of Judge Tanaka, 181.

²² Merkouris (Footnote n 15) 142–54 (discussing notably the customary law counterparts of Article 31(3)(a) and (b), and Article 32 VCLT).

²³ Somewhat confusingly, ILDC also uses the term ‘subject(s)’ in this regard.

²⁴ In the earlier publication in NILR, we also consulted Cambridge University Press’s International Law Reports (ILR). International Law Reports, however, is less user-friendly than ILDC, at least in the version I had access to via my institution. It was not possible to combine the search words ‘interpretation’ and ‘customary international law’, and unlike ILDC, the ILR application did not mark the term ‘interpretation’ in the summary or text of the decision. It was considered to be too time-intensive to copy, case-by-case, all decisions relevant to customary international law (e.g. to Word), and then apply a search for ‘interpretation’.

²⁵ See on discourse analysis at length: TA van Dijk, Handbook of Discourse Analysis (Academic Press 1985). Discourse analysis has been developed and applied mainly in linguistics, semiotics and psychology.

²⁶ Obviously, the English term interpretation is not as such used in non-English-speaking jurisdiction. However, ILDC uploads official English translations of foreign-language judgments, translates relevant parts, and/or states in the headnote’s ‘Held’ (H) sections the key holdings in English.

²⁷ The term ‘false positives’ has its origins in medical research, where it refers to errors in test results, which indicate that a disease is present which in reality is not; compare TR Dresselhaus, J Luck & JW Peabody, ‘The Ethical Problem of False Positives: A Prospective Evaluation of Physician Reporting in the Medical Record’ (2002) 28 J Med Ethics 291.

²⁸ Kiobel v Royal Dutch Petroleum Co, 621 F.3d 111 (2d Cir 2010) [58].

²⁹ Footnote ibid 155.

³⁰ US v Bellaizac-Hurtado, 700 F.3d 1245 (11th Cir 2012) 1253, citing Flores v Southern Peru Copper Corp, 414 F.3d 233 (2d Cir 2003) 247–49 (citations and references omitted) (emphasis added).

³¹ Presbyterian Church of Sudan v Talisman Energy, Inc, 244 F.Supp.2d 289 (SDNY 2003) 308.

³² See its reference to United States v Smith, 18 US 153 (1820), quoted in Filartiga v Pena-Irala, 630 F.2d 876 (2nd Cir 1980) 880 (the law of nations may be ascertained by consulting, inter alia, ‘judicial decisions recognising and enforcing [international law]’).

³³ G Betlem & A Nollkaemper, ‘Giving Effect to Public International Law and European Community Law before Domestic Courts: A Comparative Analysis of the Practice of Consistent Interpretation’ (2003) 14 EJIL 569. In the US, this is known as the Charming Betsy canon of statutory construction. Murray v The Schooner Charming Betsy, 6 US 64 (1804).

³⁴ The Minister of Justice and Constitutional Development v The Southern African Litigation Centre (867/15) (15 March 2016) South African Supreme Court of Appeal, ZASCA 17 [62].

³⁵ Public Prosecutor at the Tribunal of Brescia v Elvis and el Mahdi (9 October 2015) Supreme Court of Cassation of Italy, No 40699, ILDC 2565. The decision pertained to the question whether the expression ‘enlistment for conducting acts of violence for terrorist purposes’ in Article 270-quater of the Criminal Code (Italy), when interpreted in the light of international law, referred not only to the formal joining of armed forces, but also to the formal recruitment of enlisted persons in military or paramilitary terrorist networks.

³⁶ For example Kazemi Estate v Islamic Republic of Iran (10 October 2014) Supreme Court of Canada, Case No 35034, 2014 SCC 62; Most Rev Pedro D Arigo, et al v Scott H Swift, et al (16 September 2014) Republic of the Philippines Supreme Court, GR No 206510 (the latter court in fact applying the US Foreign Sovereign Immunities Act).

³⁷ Her Majesty the Queen in Right of Canada v Edelson (3 June 1997) Supreme Court of Israel, PLA 7092/94 [23].

³⁸ That is, the formulation of the principle of systemic interpretation of treaties in Article 31(3)(c) VCLT, which could arguably be applied mutatis mutandis to the CIL. The ILDC commentator to the Israeli case pointed out that the Supreme Court also ‘determined the content of the international law principles’, but also that it did not clearly distinguish this process from ‘their implementation in domestic law’. Her Majesty the Queen in Right of Canada v Edelson, Commentary E Peled, ILDC 577 [A2]; see the same court for a similar approach to CIL interpretation, having both international and domestic elements: Public Committee v Israel (13 December 2006) Supreme Court of Israel, HCJ 769/02, Commentary E Peled, ILDC 597 [A2] (‘as President Barak indicated elsewhere in the decision, his interpretative approach (to the concept of ‘direct participation in hostilities’ under customary international law was mandated … by the reality of Israel’s struggle against terrorism in particular’); Public Committee v Israel, Commentary E Peled, ILDC 597 [A3] (‘parts of the Israeli public who might regard the decision as excessively burdening the fight against terrorism may have been the intended addressees of … parts of the judgment’). This case is analysed in more depth in Chapter 21 by Mileva.

³⁹ O Ammann, Domestic Courts and the Interpretation of International Law: Methods and Reasoning Based on the Swiss Example (Brill 2020) 322.

⁴⁰ Footnote ibid 282 (warning for domestic courts’ self-serving interpretations and stating that ‘this risk must be mitigated if States are to interact on a level playing field’). Parochialism is one of the major ills plaguing domestic courts’ identification and interpretation of CIL: ‘courts tend to predominantly (or even solely) refer to their own State’s practice and opinio juris and to their own case law, in lieu of establishing the existence of the constitutive elements of CIL or the meaning of a customary norm on the international plane’.

⁴¹ This finding is highly significant, as it proves that customary norms can be interpreted by domestic courts. Merkouris calls such decisions ‘black swans’, which disprove the statement that ‘no swan can have any other colour other than white’ Merkouris (Footnote n 15) 143. Applied to CIL interpretation by domestic courts, this means that it suffices to identify one instance of a domestic court interpreting CIL to disprove the statement that CIL is not, and cannot be, interpreted by domestic courts. In fact, there is more than one instance.

⁴² See also Ammann (Footnote n 39) 302 (concluding her analysis of the application of customary international law by Swiss domestic courts as follows: ‘Common features include the fact that CIL is seldom mentioned, and that, when it is, it is often in cases dealing with the law of immunities’).

⁴³ For example Article 13a of the Dutch Wet Algemene Bepalingen (‘Act on General Provisions’), which provides (in old Dutch) that ‘[d]e regtsmagt van den regter en de uitvoerbaarheid van regterlijke vonnissen en van authentieke akten worden beperkt door de uitzonderingen in het volkenregt erkend’ (‘The jurisdiction of the judge and the execution of court judgments and authentic acts are limited by the exceptions recognized in public international law’).

⁴⁴ I have also applied this approach in Ryngaert & Hora Siccama (Footnote n 3) 3–5, where grounded theory is explained in greater detail.

⁴⁵ The coding has been done by me and a research assistant.

⁴⁶ See the ongoing work of the ILC on the ‘Immunity of state officials from foreign criminal jurisdiction’ (since 2007), details of which are available at <http://legal.un.org/ilc/guide/4_2.shtml>.

⁴⁷ A v Swiss Federal Public Prosecutor (25 July 2012) Swiss Federal Criminal Court, BB.2011.140 [5.4.3] (emphasis added). In the original French version:

Or, il serait à la fois contradictoire et vain si, d’un côté, on affirmait vouloir lutter contre ces violations graves aux valeurs fondamentales de l’humanité, et, d’un autre côté, l’on admettait une interprétation large des règles de l’immunité fonctionnelle (ratione materiae) pouvant bénéficier aux anciens potentats ou officiels dont le résultat concret empêcherait, ab initio, toute ouverture d’enquête.

⁴⁸ See also ILC, ‘Report of the International Law Commission: Sixty-ninth session’ (1 May–2 June and 3 July–4 August 2017) UN Doc A/72/10 175–76, Article 5 (‘State officials acting as such enjoy immunity ratione materiae from the exercise of foreign criminal jurisdiction’).

⁴⁹ Yousuf v Samantar, 699 F.3d 763 (4th Cir 2012).

⁵⁰ Samantar v Yousuf, 560 US 305 (2010).

⁵¹ Yousuf v Samantar [7].

⁵² Footnote ibid [33].

⁵³ SD Murphy, ‘Immunity Ratione Materiae of State Officials from Foreign Criminal Jurisdiction: Where is the State Practice in Support of Exceptions?’ (2018) 112 AJIL Unbound 4–8.

⁵⁴ See also Merkouris (Footnote n 15) 135–36.

⁵⁵ See notably Yousuf v Samantar [34].

⁵⁶ This is not the place to engage at length with the relationship between jus cogens and immunity, which has spawned a cottage industry of its own. See for relevant doctrine inter alia: T Weatherall, ‘Jus Cogens and Sovereign Immunity: Reconciling Divergence in Contemporary Jurisprudence’ (2015) 46 Georget J Int Law 1151–212; AJ Colangelo, ‘Jurisdiction, Immunity, Legality, and Jus Cogens’ (2013) 14 ChJIL 53–92; see also ILC, ‘Text of the draft articles on immunity of State officials from foreign criminal jurisdiction provisionally adopted so far by the Commission’ (2017) UN Doc A/72/10 175–76, Article 7(1) (‘Immunity ratione materiae from the exercise of foreign criminal jurisdiction shall not apply in respect of the following crimes under international law’).

⁵⁷ ‘Abu Omar’ case, General Prosecutor at the Court of Appeals of Milan v Adler (29th November 2012) Court of Cassation of Italy, No 46340/2012 [23.7] (interpretation emphasised).

⁵⁸ ‘It does not result from Article 38(1)(b) ICJ Statute that the domestic judge who identifies and interprets a rule of customary international law is obliged to establish in his decision the existence of a general practice admitted by a majority of States, which is at the origin of this customary rule’ [author’s own translation] NML Capital Ltd v République d’Argentine (11 December 2014) Court of Cassation of Belgium, C.13.0537 (emphasis added).

⁵⁹ ‘[D]oes not legally justify its decision by applying to embassy accounts the rule of ne impediatur legatio, assuming it were established, without first ascertaining that a majority of States admit that the rule of ne impediatur legatio also establishes an autonomous diplomatic immunity from execution of embassy accounts (violation of customary international law rule of ne impediatur legatio)’ [author’s own translation] NML Capital Ltd v République d’Argentine (emphasis added). The applicant’s primary argument was that the Court of Appeal had wrongly introduced the doctrine of stare decisis through the backdoor, by relying on a judgment of the Court of Cassation of 22 November 2012 in the same case the court held: ‘En vertu de la règle coutumière internationale ne impediatur legatio, suivant laquelle le fonctionnement de la mission diplomatique ne peut être entravé, l’ensemble des biens de cette mission qui servent à son fonctionnement bénéficie d’une immunité d’exécution autonome, se superposant à celle de l’État accréditant’ (‘By virtue of the customary international law rule ne impediatur legatio, according to which the functioning of the diplomatic mission cannot be hindered, all the property of this mission which is used for its functioning enjoys autonomous immunity from autonomous execution, superimposed on that of the sending State’ (author’s own translation).

⁶⁰ Articles 22(3) and 25 of the Vienna Convention on Diplomatic Relations (VCDR) could be considered to have codified some specific aspects of the CIL norm of ne impediatur legatio. Article 22(3) VCDR provides that ‘[t]he premises of the mission, their furnishings and other property thereon and the means of transport of the mission shall be immune from search, requisition, attachment or execution’, while Article 25 VCDR provides that ‘[t]he receiving State shall accord full facilities for the performance of the functions of the mission’. In the judgment of République d’Argentine v NML Capital LTD (22 November 2012) Court of Cassation of Belgium, C.11.0688.F held that ‘[l]’arrêt, qui, sans constater que les sommes saisies étaient affectées à d’autres fins que le fonctionnement de la mission diplomatique de la demanderesse, décide que la renonciation générale contenue dans les actes susmentionnés s’étend aux biens de cette mission diplomatique, y compris ses comptes bancaires, sans qu’il soit besoin d’une renonciation expresse et spéciale en ce qui concerne ces biens’ (‘[t]he judgment, which, without finding that the sums seized were allocated for purposes other than the operation of the plaintiff’s diplomatic mission, decides that the general waiver contained in the aforementioned acts extends to the property of this diplomatic mission, including its bank accounts, without the need for an express and special waiver in respect of such property’) violates both the VCDR provisions and the CIL norm of ne impediatur legatio.

⁶¹ This is particularly relevant for the question whether a general waiver of immunity from execution by a foreign state also extends to embassy bank accounts. If diplomatic property were to have an autonomous status pursuant to the rule of ne impediatur legatio, a waiver that specifically applies to such property would be required. For a discussion regarding the Belgian context see S Duquet & J Wouters, ‘De (on)beslagbaarheid van bankrekeningen van buitenlandse ambassades’ (2015) 16 Rechtskundig Weekblad nr 38, 1483–99.

⁶² North Sea Continental Shelf cases [74] (‘State practice, including that of States whose interests are specially affected, should have been both extensive and virtually uniform in the sense of the provision invoked; and should moreover have occurred in such a way as to show a general recognition that a rule of law or legal obligation is involved.’); A Henriksen, International Law (Oxford University Press 2017) 26 (‘While unanimity is not required, practice should include the majority of states.’). That being said, neither the ICJ nor the ILC technically require acceptance by the majority of states; see ILC, ‘Draft conclusions on identification of customary international law, with commentaries’ (Footnote n 16) 136 [3]

The requirement that the practice be ‘widespread and representative’ does not lend itself to exact formulations, as circumstances may vary greatly from one case to another … [U]niversal participation is not required: it is not necessary to show that all States have participated in the practice in question. The participating States should include those that had an opportunity or possibility of applying the alleged rule. It is important that such States are representative, which needs to be assessed in light of all the circumstances, including the various interests at stake and/or the various geographical regions.

⁶³ The lower court’s decision has not been made public (Court of Appeals Brussels, judgment of 28 June 2013), but it was summarised in the Court of Cassation’s 2014 judgment. In République d’Argentine v NML Capital LTD, the Court of Cassation did not elaborate either on its methods to ascertain or interpret the CIL norm.

⁶⁴ ILC, ‘Draft conclusions on identification of customary international law, with commentaries’ (Footnote n 16).

⁶⁵ Ryngaert & Hora Siccama (Footnote n 3) 17–21.

⁶⁶ Jurisdictional Immunities of the State (Germany v Italy: Greece intervening) (Judgment) [2012] ICJ Rep 99.

⁶⁷ Simoncioni and ors v Germany and President of the Council of Ministers of the Italian Republic (intervening) (22 October 2014) Constitutional Court of Italy, Judgment No 238/2014 [3.1] (emphasis added).

⁶⁸ Alessi and ors v Germany and Presidency of the Council of Ministers of the Italian Republic (intervening) (21 January 2014) Florence, Italy, Court of First Instance, Order No 85/2014 [18] (emphasis added).

⁶⁹ Greece v A (25 June 2014) Federal Court of Justice of Germany, BGH Urteil vom 25.06.2014 – VII ZB 24/13, Analysis by L Manthey, ILDC 2388 [A3] (emphasis added). The court itself however did not refer to interpretation and limited itself to stating as follows: ‘In German practice, the cultural institutions of foreign states were considered immune from enforcement. The promotion of culture and research by a foreign state formed part of its sovereign functions’ Greece v A [14].

⁷⁰ Jurisdictional Immunities of the State [69] (emphasis added).

⁷¹ Footnote ibid [77–78].

⁷² Footnote ibid [118] (‘it suffices for the Court to find that there is at least one condition that has to be satisfied before any measure of constraint may be taken against property belonging to a foreign State’).

⁷³ Especially in combination with the ICJ’s identification of state practice (four judgments of national Supreme Courts) Footnote ibid [118] which cites: Philippine Embassy Bank Account Case (14 December 1977) German Constitutional Court, 46 BVerfGE 342; Kingdom of Spain v Société X (30 April 1986) Swiss Federal Tribunal, 43 Annuaire suisse de droit international 158; Alcom Ltd v Republic of Colombia (12 April 1984) UK House of Lords, 1 AC 580; Abbott v Republic of South Africa (1 July 1992) Spanish Constitutional Court, 44 Revista española de derecho internacional 565.

⁷⁴ Merriam-Webster Dictionary online.

⁷⁵ Footnote ibid.

⁷⁶ C Ryngaert, ‘Embassy Bank Accounts and State Immunity from Execution: Doing Justice to the Financial Interests of Creditors’ (2013) 26 LJIL 73; C Ryngaert, ‘Immunity from Execution and Diplomatic Property’ in T Ruys, N Angelet & L Ferro (eds), The Cambridge Handbook of Immunities and International Law (Cambridge University Press 2019) 285.

⁷⁷ These circumstances may have been specified in Article 19 of the UN Convention on the Jurisdictional Immunities of States and their Properties, but it is of note that in Jurisdictional Immunities of the State the ICJ considered ‘that it is unnecessary for purposes of the present case for it to decide whether all aspects of Article 19 reflect current customary international law’ Jurisdictional Immunities of the State (Footnote n 67) [118]. Arguably, the core customary norm can be found in the first sentence of Article 19: ‘No post-judgment measures of constraint, such as attachment, arrest or execution, against property of a State may be taken in connection with a proceeding before a court of another State unless and except to the extent that …’, with the precise exceptions and circumstances being a matter of interpretation. Thus, the ICJ’s finding [118]

that there is at least one condition that has to be satisfied before any measure of constraint may be taken against property belonging to a foreign State: that the property in question must be in use for an activity not pursuing government non-commercial purposes, or that the State which owns the property has expressly consented to the taking of a measure of constraint, or that that State has allocated the property in question for the satisfaction of a judicial claim

can be considered as the interpretation or further refinement of the relative character of the core customary norm on state immunity from execution.

⁷⁸ Merkouris (Footnote n 15) 272.

⁷⁹ US v Beyle, 782 F.3d 159 (4th Cir. 2015) 169 [33] (holding that widespread acceptance of the UNCLOS provided support for its status as an accurate reflection of customary international law); Institute of Cetacean Research v Sea Shepherd Conservation Soc, 725 F.3d 940 (9th Cir 2013); see on the interpretation of treaty rules and CIL rules with the same content also Merkouris (Footnote n 15) 246.

⁸⁰ Institute of Cetacean Research v Sea Shepherd Conservation Soc.

⁸¹ Footnote ibid [6] (emphasis added), citing Castle John v NV Mabeco (19 December 1986) Court of Cassation of Belgium, 77 ILR 537.

⁸² For a similar evolving or dynamic interpretation of CIL, although not as explicit: SRYYY v Minister for Immigration and Multicultural and Indigenous Affairs (17 March 2005) Federal Court of Australia, [2005] FCAFC 42 [66] (‘The reference in Article 1F(a) of the Refugee Convention to “international instruments drawn up” clearly embraced the Rome Statute [of the International Criminal Court] … This was because the Rome Statute was expressive of customary international law.’); SRYYY v Minister for Immigration and Multicultural and Indigenous Affairs, Commentary J Navidi, ILDC 981 [A3] (the judgment ‘accepts the dynamic nature and evolution of customary international criminal law by leaving it open to the decision maker to select an instrument appropriate to the circumstances of the case’).

⁸³ L Doswald-Beck (ed), San Remo Manual on International Law Applicable to Armed Conflicts at Sea (Grotius Publications, Cambridge University Press 1995).

⁸⁴ Israel v ‘Estelle’ (31 August 2014) Haifa, Israel, District Court, Claim In Rem 26861–08–13 [42–43].

⁸⁵ Footnote ibid [48–49].

⁸⁶ Footnote ibid, Commentary D Markowicz, ILDC 2299 [A6] (emphasis added).

⁸⁷ Compare Re Víctor Raúl Pinto, Re, Pinto (Víctor Raúl) v Relatives of Tomás Rojas (13 March 2007) Supreme Court of Chile, Case No 3125–04. While neither this court nor the ILDC commentator use the term interpretation, the court arguably engages in the interpretation of CIL. The judgment considers the 1950 Nuremberg Principles, which (at least according to the court) provide for the state duty to prosecute crimes against humanity, to reflect customary international law [29]. Subsequently, it arguably goes on to interpret this customary duty in light of a later treaty development, namely Article 6(5) of Additional Protocol II to the Geneva Conventions, which calls on states parties to grant as broad an amnesty as possible [20–21]; Re Víctor Raúl Pinto, Re, Pinto (Víctor Raúl) v Relatives of Tomás Rojas, Commentary X Fuentes, ILDC 1093 [A6] (‘the Supreme Court had to reconcile Article 6(5) of Protocol II with its own interpretation of the customary law status of the duty to prosecute involved in the concept of crimes against humanity’).

⁸⁸ Ryngaert & Hora Siccama (Footnote n 3).

⁸⁹ See on the link between application, interpretation and development of international law by domestic courts: A Tzanakopoulos, ‘Domestic Courts in International Law: The International Judicial Function of National Courts’ (2011) 34 Loy LA Int’l & Comp L 135.

⁹⁰ Compare Merkouris (Footnote n 15) 264–68 (arguing that international judges prefer ‘to employ teleological and systemic interpretation instead, which are more easily distinguishable from the process of formation of customary international law’ and discounting textual interpretation as well as interpretation based on the intention of the parties).

⁹¹ Ammann (Footnote n 39) 243–45.

⁹² Her Majesty the Queen in Right of Canada v Edelson [23].