Part III - CIL and Its Interpretation in the Normative Universe

10 General Principles of Law and the Interpretation of CIL

Craig Eggett

1 Introduction

The interpretation of unwritten norms is fraught with difficulty. Without the settled text of a treaty, interpreters of unwritten norms are without a basic linguistic framework within which they may conduct their search for meaning. In such situations, the boundaries between the existence of a norm and the determination of its content can become blurred. Interpreters may return to the evidence of the norm’s existence (such as state practice) in order to determine its content or it may be that interpretation itself is part of the constitutive process of unwritten norms. This confusion is exacerbated by a lack of established methods and procedures for the interpretation of unwritten international law. Customary rules are, of course, a type of unwritten international law. Yet, custom is not alone in this category. There are other, even more nebulous, unwritten norms: general principles of law. While it is commonplace to speak of custom and general principles under the umbrella of ‘general international law’,¹ it is unclear whether questions of interpretation are to be approached in the same manner for both categories of norms or whether custom and general principles may assist in the interpretation of one another.

My central objective in this chapter is to examine the interactions between these two categories of norms in the context of interpretation. More specifically, I consider whether (and if so to what extent) general principles of law may play a role in the interpretation of customary rules. In approaching this task, I have structured the chapter in three main sections. First, it is necessary to make explicit some assumptions and presumptions about the nature of the norms under examination and the potential relationships between them. To this end, in Section 2 I clarify how I understand general principles of law – that is, as a separate kind of rules distinct from both custom and principles in the true sense of the term. In essence, I view general principles as a distinct category of (mainly secondary) rules that come into existence as a result of a dynamic process of assertion and confirmation involving a range of actors, with a particularly prominent role played by courts and tribunals. Further, I briefly sketch how, on the basis of this understanding, I view the potential relationships between general principles of law and customary law. Building on this foundation, I then turn to examine two possible roles for general principles of law in the interpretation of customary rules. In Section 3 I consider whether, as a distinct category of rules, general principles of law may form part of the legal framework relied upon when interpreting international law generally, and custom in particular. Finally, in Section 4 I examine whether it is within the scope of general principles of law to play a part in the systemic interpretation of customary rules, both as the source of the rule on systemic interpretation and as other ‘relevant rules’ of international law. The core of the argument presented in this chapter is that general principles of law could be the source of many of international law’s general rules on interpretation, including those applicable to custom, and that an enhanced reliance on general principles could facilitate further coherence in the interpretation of customary rules.

2 A Theory of General Principles in International Law

Until rather recently, ‘general principles of law’ had received considerably less academic attention than treaties and custom. The inclusion of general principles of law in the programme of work of the International Law Commission (ILC) has, in no small part, contributed to a significantly heightened interest in the subject.² Despite this substantial rise in scholarly debate on the topic, it would still be accurate to describe general principles as ‘the most enigmatic [of the] sources of international law’.³ Simply put, there is more disagreement about more aspects of general principles than the other sources. The very nature of these norms, their functions, their creation, and their importance remain unsettled questions. It is, of course, likely that the ILC’s work and the body of literature that has followed and to come will help to solidify the foundations of general principles. Yet, at this stage, it remains necessary to explicitly articulate how I understand general principles and their place in international law. This is particularly pressing as my theory of general principles has aspects that contrast with the mainstream (if there is such a thing in this field), including some departures from the positions adopted in the work of the ILC.

In short, I view general principles of law as concrete rules of law, distinct from broader, value-laden principles in the strict sense of the term. General principles, in my view, are developed not (solely) from the practice of states or through transposition from domestic law. Instead, they develop (usually incrementally) as the result of a dynamic process of assertion and contestation by a range of international actors: certain ‘systemic officials’. Courts and tribunals play a particularly prominent role in the development of general principles, and recourse to this category of rules is typically made where there is the need for a secondary rule not found in the other sources. In the sections that follow, I expand on the idea that general principles are rules, before explaining the processes through which they may be ascertained. In both parts, I endeavour to clarify the key points of distinction and interaction between general principles, on the one hand, and principles stricto sensu and customary law, on the other.

2.1 ‘General Principles of Law’ as a Category of Rules

The term ‘general principles’ is sometimes used in a rhetorical sense to convey the perceived importance or broad and general character of the norm(s) in question. A set of general rules that form the basis of an area of law may be described as general principles – a nod to their foundational character. Beyond this rhetorical use, the label may be used to capture a range of types of norms and their functions in the international legal system. For some, general principles are fundamental norms underlying the system as a whole;⁴ for others, they are considered of little importance, a class of subsidiary norms⁵ or ‘inchoate custom’.⁶ Further, general principles are occasionally conflated with other notions such equity⁷ or jus cogens norms.⁸ Against this backdrop, it is important to clarify that when I use the term ‘general principles of law’ I am referring to a distinct category of norms – namely, those referred to in the Article 38(1)(c) of the Statute of the International Court of Justice.⁹ These norms are, in my view, a separate type of unwritten rules, clearly distinct from both customary law and principles in the true sense of the term. This position is consonant with the both the history of the drafting of Article 38 and the invocation and application of general principles before international courts and tribunals.¹⁰ I take this position on the basis of my understanding of the foundations of the international legal system as a whole and, while it would be impractical to explain this fully here,¹¹ central to this understanding is the distinction of kind between rules and principles.

Reference to general principles within the meaning of Article 38(1)(c) of the ICJ Statute is distinct from reference to principles in the strict sense of the term. Principles stricto sensu are value-based optimisation commands that influence the development and interpretation of rules¹² and can frequently be expressed as ‘should’ statements. As such, they are wholly separate from rules, which issue definitive commands following the fulfilment of one or more conditions.¹³ Of course, that general principles and principles stricto sensu are distinct does not mean that they operate in isolation. There are meaningful interactions between all categories of norms in the international legal system, with rules (including general principles of law) giving concrete legal expression to principles stricto sensu. In turn, principles perform a guiding role in international law, influencing the interpretation and development of the system and the application of its rules. The extent of this interaction between principles and rules may differ depending on the context and norms in question. It may even be that there is a closer relationship between principles and general principles then there is between principles and other categories of rules. It may also be that it is (only) through a general principle of law that a principle stricto sensu is granted protection in international law through the imposition of a specific obligation. Nevertheless, such a close relationship would not detract from the existence of the distinction between the two.

If this distinction between general principles and principles stricto sensu is accepted, questions arise as to the distinction between general principles and customary law. Both of these are unwritten norms of (predominantly) general application. Yet, once again, it should be made clear that custom in the sense of Article 38(1)(b) of the ICJ Statute refers specifically to a category of unwritten rules. So, references to ‘customary principles’ or ‘principles of customary law’ are,¹⁴ in my view, references to principles in the strict sense of the term and distinct from the customary rules that generate specific legal rights and obligations following from the existence of the required state practice and opinio juris.¹⁵ While, as with any of the sources of international law,¹⁶ there is scope for overlap, custom and general principles tend to perform distinct functions. Customary rules tend to be primary rules;¹⁷ they impose obligations and grant rights, generally to states, on the basis of their general practice and acceptance that such practice is legally expected. General principles, conversely, are generally secondary rules¹⁸ that arise in the context of dispute settlement and in the absence of an applicable treaty or customary rule.¹⁹ This distinction in function between general principles and custom is linked to the distinctions between the respective means through which these kinds of rules are ascertained. This is further explained in Section 2.2.

2.2 Ascertainment by ‘Systemic Officials’: The Centrality of Courts and Tribunals

Like all rules, general principles must be ascertained on the basis of certain criteria. It is clear that Article 38(1)(c)’s reference to ‘civilized nations’ is problematic and cannot be maintained. Already in the North Sea Continental Shelf case, Judge Ammoun noted that this term is inconsistent with the UN Charter and was introduced as a form of power politics by European colonial powers.²⁰ Judge Ammoun advocated for a more inclusive approach when referring to domestic systems of law, calling for the term ‘civilized’ to be dropped and referring to (the far more inclusive) ‘universal’ support for general principles by ‘all … nations’.²¹ While not expecting universal support, the recent work of the ILC seems consonant with Judge Ammoun’s basic position, with the current version of Draft Conclusion 2 stating: ‘For a general principle of law to exist, it must be generally recognized by [the community of nations].’²² The ascertainment of general principles is the focus of the ILC’s Second Report,²³ and eight of its fourteen Draft Conclusions are concerned with this topic.²⁴ In short, and from the starting point of general recognition by the community of nations, the ILC’s position on ascertainment is predicated on a distinction between general principles that are derived from domestic systems and those that are formed within the international legal system.²⁵ From this foundation, the ILC proceeds to elaborate on the processes through which each kind of general principle is formed. For general principles of domestic origin, the ILC adopts a two-step approach requiring ‘(a) the existence of a principle common to the principal legal systems of the world; and (b) its transposition to the international legal system’.²⁶ Here, it is clear that the ILC follows the trend of reliance on a comparative approach to domestic systems,²⁷ with Draft Conclusion 5 explaining that:

1. 1. To determine the existence of a principle common to the principal legal systems of the world, a comparative analysis of national legal systems is required.

2. 2. The comparative analysis must be wide and representative, including different legal families and regions of the world.

3. 3. The comparative analysis includes an assessment of national legislations and decisions of national courts.²⁸

On the issue of transposition, the ILC makes reference to the need for a general principle to be compatible with ‘fundamental principles of international law’ and notes that it must be the case that ‘the conditions exist for its adequate application in the international legal system’.²⁹ In relation to the latter requirement, the ILC explained that this concerns the suitability or appropriateness of a prospective general principle to be applicable in inter-state relations.³⁰

When it comes to general principles that are formed within the international legal system, the ILC notes three factors for their ascertainment in Draft Conclusion 7 – namely, that:

1. (a) a principle is widely recognized in treaties and other international instruments;

2. (b) a principle underlies general rules of conventional or customary international law; or

3. (c) a principle is inherent in the basic features and fundamental requirements of the international legal system.³¹

While these appear to be alternative, the special rapporteur notes that these forms of recognition are not mutually exclusive and that they may co-exist as evidence of wide and representative recognition of a general principle by states.³²

The ILC’s account of the ascertainment of general principles is, of course, extremely helpful in exploring this foundational issue. I would, however, question the persistence of the distinction between general principles of domestic law origin and those that develop purely on the international plane.³³ In my view, following from the requirement of general recognition, the focus should be on whether there is sufficient international support for the identification of an international norm.³⁴ While prevalence in domestic systems may be an important factor in the ascertainment of general principles, the drawing of a distinction between general principles of a domestic origin and international general principles is an oversimplification. All general principles must find the required level of support in international law. The idea of transposition from domestic to international law, while going some way in acknowledging this need, is inadequate. This is for two related reasons. First, the notion that a common core of a norm can be extrapolated from domestic systems to the international legal system is rather artificial. Reference to domestic systems may support the idea that a prospective norm is linked with notions of legal logic, but the act of transposition is, in essence, the same as establishing recognition in and consonance with international law. Second, it does not reflect the reality that a norm applicable only in a handful of domestic systems may nevertheless become a general principle if it finds support from other actors, instruments, or norms. In asserting the existence of a prospective general principle, actors can (and do) refer to both domestic and international sources in support of their claim. Put differently, there is a certain overlap between the factors referred to in Draft Conclusions 5 and 7.

As noted by the ILC in its Second Report, there is potential overlap between the evidence used in the ascertainment of general principles and that used for the identification of custom, particularly when it comes to domestic legislation and judicial decisions.³⁵ In the view of the ILC, the distinction between the methodology used to identify each source is preserved by the need for opinio juris for custom and transposition in the case of general principles.³⁶ In my view, while there is indeed some overlap between these sources, the distinction in ascertainment methodologies boils down to the fact that the centre of gravity for custom is the practice and views of states, while with general principles of law this lies with a broader range of actors, particularly courts and tribunals. States are indeed relevant for general principles, and it may be that a general principle may not form contrary to the will of states, but there is no need to identify a link to the subjective and objective position taken by a majority of states, as is the case with customary law. I acknowledge here that this position is predicated on what may be considered a narrow understanding of the constitutive elements of custom. If it is assumed that there is a more significant role for non-state actors in the creation of custom, then the distinction between the two categories of unwritten rules becomes blurred and it may be more sensible to label all unwritten rules as custom and to equate general principles with principles in the true sense. However, this position is not consonant with the drafting of the PCIJ Statute, the practice of courts and tribunals,³⁷ or the position of the ILC. It is with this understanding of general principles in mind that the discussion in subsequent sections is developed.

3 General Principles as Part of the Interpretative Architecture of International Law

It has been argued that international law on interpretation has a ‘treaty focus’,³⁸ meaning that ‘international legal interpretative doctrine remains firmly rooted in the law of treaties, even as scholars push for a wider lens’.³⁹ Explaining this position, Duncan Hollis refers to the challenges present in the ascertainment of unwritten sources, which results in the central position of treaties, specifically the rules contained in Articles 31 and 32 of the Vienna Convention on the Law of Treaties (VCLT) of 1969,⁴⁰ in the body of norms that guide the interpretation of international law.⁴¹ Indeed, it is clear that the VCLT rules are core elements in the interpretative architecture of international law, with both judicial decisions⁴² and academics⁴³ asserting that they form part of customary international law. On the basis of the aforementioned understanding of general principles and customary law, it is arguable that such assertions are not commonly supported by reference to the required state practice and opinio juris. That being said, this is largely a question of semantics, as I would not question that these rules are part of general international law. Yet, from this starting point, two issues arise in relation to the interpretation of customary international law. First, whether the general international law equivalents of the VCLT rules apply to unwritten rules (in the same way as they do to treaties) and, second, whether there are other norms at play in the interpretation of international law.

Precisely mapping this interpretative infrastructure is a challenging task, particularly in the case of unwritten rules, where the lines between law ascertainment and content determination (interpretation) may appear difficult to draw.⁴⁴ Nevertheless, as a preliminary matter, it should be made clear that interpretation of customary rules is not only possible, but necessary.⁴⁵ While there are key differences between the interpretation of written and unwritten rules, the content of all rules will be expressed in written form of one kind or another. Naturally, the processes of ascertainment of unwritten rules may themselves involve interpretation of some kind, but this does not change the fact that the content of the rules will be subject to interpretation once they have been ascertained.⁴⁶ Put differently, the criteria for the existence of a customary rules are distinct from the rules as such.⁴⁷ The interpretation of custom should thus be viewed as ‘the act of determining/construing the content of customary rules the existence of which is unchallenged’.⁴⁸

My central argument in this section is that general principles of law could play a key role when considering these questions in the context of interpreting customary rules. If, as asserted, general principles are a distinct category of (predominantly) secondary rules, they could serve as a basis for international law’s general rules of interpretation, in particular in the case of interpreting unwritten rules such as those of customary international law. Before expanding on this claim further, it is necessary to consider the normative composition of the interpretative architecture of international law. In seeking to describe this legal framework, authors and judges have deployed a range of terms to denote differences in the nature, function, and origin of norms that aid the process of interpretation.

3.1 Maxims, Methods, Principles, and Rules of Interpretation

The body of international law concerned with interpretation is normatively heterogenous. In other words, the task of interpreting an international legal rule is not regulated by rules alone;⁴⁹ the process of interpretation is ‘highly context-specific’.⁵⁰ It may even be argued that there is such a high degree of discretion for interpreters that there is but a marginal role for norms that guide this process.⁵¹ The reality of this discretion does not, it is argued, remove the relevance of norms of interpretation. There are norms that regulate the approach taken by interpreters, but it can be very difficult to determine the existence and content of these norms. This difficulty is reflected in the terms used to explain approaches to and limits of interpretation in international law. For example, reference has been made to ‘rules’,⁵² ‘principles’,⁵³ ‘methods’,⁵⁴ and ‘maxims’⁵⁵ of interpretation. The intended content of such labels may differ depending on the user, but an essential distinction for present purposes is that between concrete (definitive) rules of interpretation and other norms and notions that may provide (non-definitive) guidance for those engaging in the task of interpretation. Specific rules on interpretation may regulate the basic steps that must be taken by, or impose certain obligations on, the interpreter in specific situations. For example, it may be a rule that the first port of call must always be the text itself or that certain methods can be used only if others fail.⁵⁶ Other norms – certain maxims or principles of interpretation – may simply provide general guidance or relevant factors for the process of interpretation while not mandating a specific course of action for the interpreter. A potential example of such a norm is the notion of per analogiam interpretation.⁵⁷ While the relevance and scope of this notion in international law are unsettled,⁵⁸ it would seem that this would merely be a tool to be used at the discretion of the interpreter to aid in their task.

The precise scope of a prospective norm of interpretation is not always clear and there may be overlap between different notions. Yet, as explained, the initial task when mapping this legal framework should be a distinction between rules of interpretation and other, non-definitive, norms. Indeed, in my view, the legal framework for the interpretation of international law consists of a collection of rules and principles. It seems, however, that this framework is not clearly and comprehensively defined. There are a number of prospective or candidate norms that may – or may not (yet) – be part of international law. These candidate norms are commonly linked to basic notions of legal logic and their existence in a range of domestic law systems, and may be expressed in the form of certain Latin maxims.⁵⁹ The connections with notions of legal logic and domestic law suggest a role for general principles of law in the development of this interpretative framework. As explained above, general principles in the sense of Article 38(1)(c) of the ICJ Statute are frequently explained with reference to basic ideas of legal law and a comparative examination of domestic systems. Yet, the exact role of general principles will, once again, depend on the position taken on the nature of this category of norms. According to my understanding of general principles as a distinct category of rules, only accepted norms that impose concrete obligations on the interpreter can be considered as general principles of law in the sense of Article 38(1)(c) of the ICJ Statute. Other general, non-definitive, norms that may be found in domestic systems do not fall within this category. However, it may be that they are accepted principles stricto sensu providing first-order and non-definitive reasons to reach a particular result without specifically requiring this. To reiterate, the position taken here is not aimed at minimising the potential impact of such principles, which may effectively facilitate a pragmatic approach to interpretation in international law.

3.2 General Principles as Rules of Interpretation (of Custom)

It is clear that there are such things as rules of interpretation in international law. This much is evident from the VCLT of 1969. Typically seen as embodying the ‘general rule’ on interpretation,⁶⁰ Article 31 of the VCLT of 1969 imposes obligations on interpreters to take into account certain factors and circumstances surrounding the language, background, and broader context of the rule in question. These rules impose obligations of conduct on interpreters, yet there is certainly room to place the emphasis on different factors and circumstances. Within the general rule of Article 31(1) of the VCLT of 1969, for example, it is generally considered that there is no hierarchy of elements and that the different aspects listed – good faith, ordinary meaning, context, and object and purpose – should be considered as part of a single process.⁶¹ The rules in the VCLT are, of course, treaty rules. If there are more generally applicable rules of interpretation, they will have to be based on another source of international law: either custom or general principles of law. Indeed, the mainstream position is that any general rules on the interpretation of international law are grounded in custom. This is true for the general international law equivalents of the VCLT rules, which have been held as part of customary law.⁶² In Sections 3.2.1 and 3.2.2 it is argued that general principles of law will frequently be a more appropriate basis for such generally applicable rules of interpretation.

3.2.1 The Case for General Principles as a Source of Rules of Interpretation

As a preliminary point, it should be noted that rules of international law may be based on multiple sources of law. That is to say, similar or identical rules emanating from different sources – treaties, custom, or general principles – may exist and apply in parallel.⁶³ Therefore, rules of interpretation that are present in one source – say, a treaty such as the VCLT of 1969 – may also exist as custom and/or general principle of law. In many instances, then, the presence of a norm of general international law (custom or general principle) may be irrelevant where there is a treaty rule applicable to the party in question.

It is clear that there are rules of interpretation beyond the specific context of the VCLT of 1969, even if it is merely the case that the VCLT rules have general international law equivalents. Indeed, the rules reflected in the VCLT have been deemed to apply both to treaties that pre-date their codification in the Vienna Convention⁶⁴ and to other sources of law,⁶⁵ thereby necessitating their existence in general international law. A rule found in the VCLT of 1969 has a different scope of application from an identical customary rule or general principle. Not only could such a rule apply to all treaties; it could also apply to rules emanating from the other sources of law, in particular customary rules.⁶⁶ There is, therefore, a need to determine whether such unwritten rules exist. As mentioned, it is most commonly asserted that the application of these rules beyond the context of the VCLT is due to the parallel existence of these rules as custom. This position is consonant with the broader trend to equate all unwritten rules of international law as customary. Given that customary international law is a clearer concept (or at least, less unclear) than general principles, this is unsurprising. Indeed, this claim may, in many circumstances, have merit; customary law has clearly been instrumental in the development of the international legal system. Yet, such arguments should be examined more closely, as there are significant implications for automatic (over-)reliance on custom as a vehicle for such rules. While there may be general rules of international law that fulfil the requirements of customary law, it should not be assumed, as is frequently the case, that all general international law rules are grounded in custom. As Sir Robert Jennings observed, ‘most of what we perversely persist in calling customary international law is not only not customary law; it does not even faintly resemble customary law’.⁶⁷

The process for the determination of custom has traditionally centred on the fulfilment of two elements: widespread and consistent state practice and the accompanying belief by states that such conduct is legally required (opinio juris).⁶⁸ The formation of custom has received renewed attention in the recent work of the International Law Commission (ILC), which sought to provide further guidance on the identification of customary rules.⁶⁹ While acknowledging the broader context in which these two elements must be assessed,⁷⁰ the ILC reaffirmed the focus on the two elements of custom and the centrality of states to the formation of customary rules.⁷¹ While the ILC specified the need for ‘systematic and rigorous analysis’ of state practice and opinio juris in assessing the formation of a customary rule, it has been widely noted that this is seldom the case in reality, with courts simply asserting the existence of a customary rule with little or no evidence.⁷² This is, of course, unsatisfactory. The existence of all international legal rules is premised on the fulfilment of conditions of validity and the fulfilment of these conditions must be supported by evidence. For customary rules, this evidence is found in the actions and views of states. This evidence may be assessed by courts and tribunals, but the focus is on what states are doing and claiming. Yet, many rules of interpretation – like many other secondary rules – have developed in international law through the decisions of international courts and tribunals, as it is predominantly these actors that are faced with the task of interpretation. In many instances, it would not be accurate to say that these rules have fulfilled the requirements of custom. The rules have developed out of necessity, with reference to domestic law and the broader context and features of the international legal system. It may be argued that the assertion of such norms by states before international courts and tribunals is sufficient to demonstrate their customary status. At best, the assertions of states may be seen as evidence of opinio juris, but it is rarely the case that the practice of states supports the existence of such norms. The actor relevant in the act of interpretation is, typically, a judicial body. Questions of interpretation come before international courts and tribunals, which, in the absence of established norms, search for and confirm the existence of rules governing the process of international adjudication. In determining the existence and content of such rules of interpretation, as with many other secondary rules in international law, courts and tribunals have not limited themselves to an assessment of the elements of customary law but have had recourse to a broader range of factors, including domestic law and principles stricto sensu.⁷³

3.2.2 Candidates for General Principles of Interpretation

As mentioned, some of the general rules of interpretation of international law – whether based in custom or general principles – will also be treaty rules contained in the VCLT. In the context of the law of treaties and on the basis of the jurisprudence of the ICJ, Sir Gerald Fitzmaurice compiled a list of six principles of interpretation.⁷⁴ These were:⁷⁵ (1) the principle of actuality (textuality); (2) the principle of natural and ordinary meaning; (3) the principle of integration;⁷⁶ (4) the principle of effectiveness; (5) the principle of subsequent practice; and (6) the principle of contemporaneity. These principles set out a general process for the interpretation of international rules, which was later taken up in the drafting of the VCLT of 1969. Indeed, many of the notions identified by Fitzmaurice and later included in the VCLT have a long history in the decisions of international courts and tribunals,⁷⁷ as well as established pedigree as basic elements of legal logic in domestic systems. Some of these principles may be more difficult to apply in the context of the interpretation of customary rules. For example, it may be more difficult to apply the principle of integration to a rule not based in a specific and authoritative text. Further, there are inherent difficulties that arise in assessing subsequent practice in the context of customary rules, as questions may arise as to whether such practice is part of the formation of new rules or the interpretation of existing rules. Nevertheless, on the basis of the historical background to these principles and their subsequent acceptance in the VCLT and judicial decisions, it seems convincing that they form part of general international law and so could be used as an approach to the interpretation of customary rules. Yet, as described above, it should not merely be assumed that these general rules are customary, as their acceptance has not been a clear result of the actions and views of states but of judicial bodies striving for a framework of secondary rules to aid in the task of interpretation in the absence of an applicable treaty rule.

In addition to, or perhaps as part of, the basic rules reflected in the VCLT of 1969, it may be possible to argue for the existence of other rules of interpretation grounded in general principles. A clear candidate includes the uncontroversial proposition that an interpretation of a rule cannot contradict a jus cogens norm.⁷⁸ Indeed, this interpretation rule is logical given the nature and role of jus cogens norms and the consequences of their violation. This was advanced by the Islamic Republic of Iran in the Oil Platforms case, where it was argued that:

Under Article 53 of the Vienna Convention … a provision of a treaty which conflicts with a norm of jus cogens is void … That is to say, the treaty as a whole is void. These rigorous provisions must in turn generate a stringent principle of interpretation, so that any provision of a treaty is to be interpreted, if at all possible, so as not to conflict with such a rule.⁷⁹

While not specifically endorsing the rule of interpretation as formulated by Iran, the ICJ explained that it was required to interpret the treaty rule in question (Article XX of the Treaty of Amity⁸⁰) in conformity with the rules on the use of force.⁸¹ The existence of such a rule has been recently confirmed by the ILC in the context of its work on jus cogens.⁸²

There are other candidates for rules of interpretation that should be classified as general principles of law. Whether these prospective norms are to be considered as general principles of law or principles stricto sensu will depend on their precise scope and content. Take, for example, the collection of ‘maxims’/‘cannons’ of interpretation in the practice of the PCIJ and ICJ, as identified by Merkouris and Peat.⁸³ The scope for notions such as in dubio mitius,⁸⁴ effet utile,⁸⁵ and per analogiam⁸⁶ to constitute general principles of law will very much depend on their precise context in the international legal system. It is beyond the scope of this chapter to consider these notions/norms in detail, but what is critical is whether courts and tribunals elucidate clear conditions for their application and whether this involves the imposition of obligations on the interpreter. There is considerable practice in support of such norms, and so it seems that there is potential for the development of rules in the form of general principles here. That being said, depending on the precise content of the norm, it may be that these norms amount to principles stricto sensu. For example, the ‘principle of effectiveness’ is clearly viewed as part of international law and as being of relevance to the interpretation of international rules.⁸⁷ Its precise content, however, is less clear. It may, for example, not require an interpreter to strive to assign the greatest possible effectiveness to a rule, but instead merely to seek to avoid an interpretation that avoids depriving a rule of any effects altogether.⁸⁸ In this sense, it may be seen to underlie the general rules of interpretation set out in Article 31 of the VCLT of 1969.⁸⁹ Whether such norms are considered general principles of law will depend on courts and tribunals continuing to deliberate on them.

4 General Principles, Custom, and Systemic Interpretation⁹⁰

A particularly prominent tool in the interpretation of unwritten rules is the notion of systemic integration. More precisely, against the background of broader principles of coherence and consistency in the international legal system,⁹¹ there is a specific rule of systemic interpretation. This rule requires that interpreters take into account ‘any relevant rules of international law applicable in the relations between the parties’.⁹² The central objective of this rule of interpretation is coherence and consistency in the international legal system. The development of general principles of law, too, has links to such notions. This final section explores the interaction between this rule of systemic interpretation and general principles in international law. Once general principles are understood to be rules, two issues arise with regard to systemic interpretation: first, whether this rule on systemic interpretation can itself be considered a general principle and, second, whether and how the interpretation of customary rules occurs in light of general principles as ‘relevant rules of international law’.

4.1 Systemic Interpretation as a General Principle of Law

The idea that international rules should be interpreted coherently and consistently with the normative environment in which they exist is inherently attractive. Such coherence is linked to the idea of international law as a legal system, and the imposition of an obligation on interpreters to respect and facilitate this systemic coherence is a logical foundation of the international legal order.⁹³ McLachlan has claimed that systemic integration has the status of a ‘constitutional norm’ in international law.⁹⁴ It is clear that the obligation to systemically interpret international rules has a strong pedigree in the international legal system, perhaps as an ‘unconscious part of the interpretation process’.⁹⁵ While undoubtedly part of international law beyond the VCLT of 1969, it may be questioned whether the rule on systemic interpretation is customary, as is the standard claim, or whether it is better conceived of as a general principle of law. It is clear that this norm is a rule of international law, more specifically one that imposes an obligation of conduct on interpreters to ‘take into account’ certain factors. Further, it should be noted that this rule has a long history in the decisions of courts and tribunals,⁹⁶ including by the ICJ in Oil Platforms.⁹⁷ The prominence of courts and tribunals in the development of this international rule, together with its close relationship with principles stricto sensu (such as coherence⁹⁸), suggest its characterisation as a general principle as opposed to a customary rule.

4.2 General Principles as ‘Relevant Rules of International Law’

Already in the Georges Pinson case reference was made to the need to interpret rules in accordance with ‘general principles of international law’.⁹⁹ If general principles of law are rules, they are rules of general application.¹⁰⁰ It therefore seems they could frequently play a role as ‘relevant rules of international law applicable in relations between the parties’. However, two clarifications should be made here. Firstly, frequent recourse to something labelled as a ‘(general) principle’ may not be reference to a general principle in the sense of Article 38(1)(c) of the ICJ Statute. Instead, this may be a reference to principles stricto sensu.¹⁰¹ For example, reference may be made to ‘general principles’ such as ‘sovereignty’¹⁰² or ‘humanity’¹⁰³ when approaching the interpretation of rules. These, of course, play a key role in interpretation as they help determine the meaning of rules to which they are related, but this practice is not part of the obligation to consider other applicable rules.¹⁰⁴ Second, it should be emphasised that there is a need to identify relevant rules for the purposes of systemic interpretation. This would cover rules that exist in parallel in multiple sources, but it may also cover rules that deal with similar subject matter or adopt similar wording.¹⁰⁵ It will be recalled that general principles, partly due to the process of their ascertainment, tend to be secondary rules that emerge in the absence of any treaty or customary rules. As such, the scope for parallel or overlapping rules may be more limited than in the case of interpretation in the light of treaties or custom, which tend to concern primary rules.

There are examples in which courts and tribunals seem to have interpreted rules against the backdrop of general principles. For example, in Golder v. United Kingdom, the European Court of Human Rights referred explicitly to Article 38(1)(c) of the ICJ Statute, concluding that there was a general principle of law regarding access to civil courts when interpreting Article 6 of the European Convention on Human Rights.¹⁰⁶ Similarly, in Furundžija the Trial Chamber of the International Criminal Tribunal for the Former Yugoslavia was tasked with determining the scope of the offence of rape in its statute. The chamber conducted a review of domestic approaches to this question and made reference to the principle (stricto sensu) of human dignity.¹⁰⁷ It should be noted that in such cases there may be a need to identify a prospective general principle before it can be used in the systemic interpretation of a treaty or customary rule. As mentioned at the outset, general principles of law have received comparatively little attention in international law. There is, therefore, significant unrealised potential for their use as a tool for the development of new rules. In some fields, this potential may also include scope for the development of new primary rules of international law.¹⁰⁸ For example, there are several unwritten primary rules in international environmental law that seemed to originate not in the practice of states but in the reasoning of courts and tribunals. These include the obligation to prevent transboundary harm¹⁰⁹ and the obligation to notify other states in the event of such harm.¹¹⁰ It may be expected that the renewed interest in general principles in scholarship and by the ILC may lead to a greater role played by these norms in the development of new international rules. If this is the case, the scope for general principles to influence the systemic interpretation of customary rules would be further enhanced.

5 Concluding Remarks

This chapter has explored the interface between two developing fields at the very foundations of international law: the nature of general principles of law and the interpretation of customary rules. Central to the ongoing discussion on the nature, function, and place of general principles in the international legal system is the question of the interaction between general principles and other international legal norms. Questions of interpretation are a prominent area of such interaction, and, assuming general principles to be secondary rules of international law, there is significant potential for the development of general principles of interpretation. For the most part, the discussions sketched in this chapter may appear to amount to an exercise in (inconsequential) labelling. Yet, when approaching a task as challenging as that of mapping the interpretative architecture of custom, the labels used matter. As important as customary rules are, it is inaccurate to use ‘customary international law’ as shorthand for any and all norms beyond treaties. There are clear distinctions to be drawn between the different categories of rules and principles that constitute ‘general international law’. This exploration of the role of general principles in the interpretation of custom illustrates the normative heterogeneity of general international law, providing a foundation for further examination of the precise contours of the structures that govern the interpretation of unwritten rules and other systemic questions of international law.

11 Interpretation of Customary Rules by Reference to Treaties and General Principles of Law

Marina Fortuna

1 Introduction

In its case law, the International Court of Justice (ICJ) has repeatedly suggested the idea that rules of customary international law (CIL) do not operate in a vacuum but, instead, are to be understood against the background of other rules of the international legal system.¹ This observation, although somewhat unsurprising, shows that the sources of international law exist in close interconnection – something that is also visible if one looks at the rules of interpretation contained in Article 31 of the Vienna Convention on the Law of Treaties (VCLT). Accordingly, ‘any relevant rules of international law applicable in the relations between the parties’ must be taken into account, together with the context, when interpreting treaty provisions.² The question addressed in this chapter is whether or not the same can be said of the interpretation of customary rules. In other words, if we look at the practice of international courts and tribunals, is it possible to reach the conclusion that CIL rules, too, must be interpreted with the cognizance of any relevant rules of international law applicable between the parties?

To answer this question, I have enquired into the practice of international courts and, in particular, into the ways in which, if at all, they use treaties and general principles of law – the other two sources of international law contained in Article 38 of the ICJ Statute – to interpret the content of customary rules. Here, following my previous writings on the subject of CIL interpretation, I understand interpretation as an act of discerning the content and scope of the customary rule, rather than interpreting the elements of custom – state practice and opinio juris. While in this chapter I engage in a critical reading of the judgments, I leave aside as being outside the scope of this chapter my musings on the interpretability of CIL.³

According to the ILC’s draft conclusions on the identification of CIL, other rules, such as those contained in treaties, can aid determination of a customary rule’s existence.⁴ Our focus, then, will be on studying the judgments of international courts with a view to demonstrating how they use treaties and general principles to establish the content of customary rules whose existence is not disputed by the parties.⁵

To facilitate the analysis of the case law and the accompanying argumentation, the chapter has been structured in three sections. Section 2 unpacks the various meanings of systemic interpretation that can be found both in legal scholarship and in practice and which will be used as an analytical framework for the subsequent analysis. Sections 3 and 4 analyse the case decisions in which international courts and quasi-judicial bodies have used treaties and general principles of law in construing the content of customary rules. Section 5 examines case law in which the interpretation of a CIL rule is carried out by reference to the body of rules of which it is part.

2 The Multiple Meanings of Systemic Interpretation as an Analytical Framework

It is common practice among international courts and tribunals to use customary rules to interpret treaties. One frequently cited example is the Jan Mayen case, where the ICJ stated that Article 6 of the 1958 Convention on the Continental Shelf must be interpreted and applied by reference to customary law.⁶ Pronouncements similar to those made in the Jan Mayen case usually fall within the ambit of Article 31(3)(c) of the VCLT, according to which ‘any relevant rules of international law applicable in the relations between the parties’⁷ must be taken into account, together with context, in interpreting treaty provisions. This rule is usually referred to in case law and literature as the principle/rule of systemic interpretation⁸ or systemic integration.⁹ Confusingly, however, both of these terms have been used to convey not one but four different meanings.

Firstly, a textual analysis of Article 31(3)(c) shows this paragraph to be part and parcel of the core rule according to which treaty provisions must be interpreted in accordance with the ordinary meaning the words are to be given in their context and in the light of their object and purpose. In addition to context, Article 31(3)(c) states that any relevant rules of international law applicable in the relations between the parties must be taken into account in the determination of the ordinary meaning of the terms. As aptly noted by Tzekvelos, ‘Article 31(3)(c) expands the semantic field of the provisions of a convention’.¹⁰ One example of this is when interpreters look at the use of the same term in another treaty that is in force between the parties and use it to further a particular understanding of the term. This is the first meaning of systemic interpretation.

The second meaning that has been ascribed to systemic interpretation is that of an interpretation of a rule against the background of the system of law as a whole. At the Institut de Droit International, this position was expressed by Verdross, who stated that ‘a treaty must be interpreted in light of general law and general principles of law’.¹¹ According to the ICJ, ‘a rule of international law, whether customary or conventional, does not operate in a vacuum; it operates in relation to facts and in the context of a wider framework of legal rules of which it forms only a part’.¹² Depending on how it is applied, this meaning of systemic interpretation may either converge with the first meaning – if the ordinary meaning is determined by reference to these other principles or rules – or go beyond it and result in what Alexy and Adler describe as the use of systemic arguments in interpretation.¹³

This second meaning is markedly different from what Article 31(3)(c) prescribes,¹⁴ which is to use any relevant rules for the determination of ordinary meaning in the light of context and of object and purpose. It is important to note that Article 31(3)(c) mentions the use of any relevant rules applicable between the parties and not any relevant rules generally. Only reference to all relevant rules would in fact suggest that the rules as a whole should be taken into account for interpretative purposes. According to this second understanding, systemic interpretation is essentially a use of systemic arguments that involves placing the rule in the system of international law as a wider form of context.¹⁵

Another meaning of systemic interpretation is reflected in Verzijl’s dictum in the Georges Pinson Case, where he noted that every treaty must be considered to refer tacitly to general principles of international law for all those matters that it does not clarify in express terms.¹⁶ This is different from systemic interpretation as meaning that other relevant rules must be used to determine the sense to be given to the words used in the treaty. Instead, it is a form of gap-filling, a technique to avoid a pronouncement of non liquet. And while Verzijl’s statement conditions recourse to general principles of law on the lack of an express resolution of the issue in conventional rules, systemic interpretation/integration has also been argued to support what essentially is an incorporation of extraneous rules and their application to the case, even when there is no clause providing for such reference.¹⁷ The issue here is that the use of what is termed systemic interpretation would in this case be in violation of the obligation of good faith in interpretation.¹⁸ Moreover, as Moreno-Lax rightfully points out, ‘Article 31(3)(c) VCLT should indeed be taken as a rule of interpretation, rather than a source of directly applicable law’.¹⁹

Finally, systemic interpretation or integration has also been interpreted in a way that equates it with an interpretation that allows for co-ordination of norms in the case of indirect or, what de Wet and Widmar call, broad normative conflict.²⁰ The case law of the ECtHR, which refers to it as harmonization, is a good example of this approach,²¹ although, strictly speaking and interpreting the Article 31(3) holistically, it goes beyond what Article 31(3)prescribes. In the words of Tzevelekos, the European Convention on Human Rights ‘benefits from the latter [international law] through absorption of normative elements which, although absent from its “imperfect” text, are both complementary and necessary for the effective promotion of its special scopes’.²²

To sum up, this means that other rules may essentially fulfil four different functions, all under the label of systemic integration: (1) other rules may serve as an aid to determine the ordinary meaning of the terms; (2) other rules may be used as a tool for systemic arguments; (3) other rules may be used as tools for gap-filling; or (4) other rules may be used as a tool for the resolution of a normative conflict. The latter two go beyond our understanding of interpretation. I will use this framework as a reference point for my analysis, in the following three sections, of case law where customary rules have been interpreted.

3 Interpretation of Customary Rules by Reference to Treaties

While, according to Article 38 of the ICJ Statute, international custom is a separate source of law, it exists in close interconnection with the other sources of international law. This is clear from the ILC’s draft conclusions, according to which ‘[v]arious materials other than primary evidence of alleged instances of practice accepted as law (accompanied by opinio juris) may be consulted in the process of determining the existence and content of rules of customary international law’.²³ Such materials include ‘treaties, resolutions of international organizations and intergovernmental conferences, judicial decisions (of both national and international courts), and scholarly works’.²⁴ The ILC then adds that ‘such texts may assist in collecting, synthesizing or interpreting practice relevant to the identification of customary international law, and may offer precise formulations to frame and guide an inquiry into its constituent elements’.²⁵

According to an empirical study conducted by Choi and Gulati, treaties are the most frequently used materials for the identification of customary rules.²⁶ Treaties can codify, crystallize and even generate customary rules.²⁷ Treaties that codify pre-existent custom are known as declaratory, and whether a treaty is declaratory of CIL is determined by analysing the preamble of the treaty or by looking at the travaux préparatoires for confirmation that this was the intention of the parties.²⁸ Most treaties, however, fall into the category of partly declaratory treaties,²⁹ meaning that some provisions are codifications, whereas others are not.

At the same time, because treaties and custom originate from two different processes of law creation,³⁰ treaties do not absorb CIL even when they codify it. This means that custom does not cease to exist upon being codified; it runs its course parallel to the treaty.³¹ This is what the ICJ conveyed through the following statement in the Nicaragua case:

even if a treaty norm and a customary norm relevant to the present dispute were to have exactly the same content, this would not be a reason for the Court to take the view that the operation of the treaty process must necessarily deprive the customary norm of its separate applicability.³²

Moreover, as the ICJ argued, custom continues to apply even between the states that are parties to the treaty.³³ This means that while different in nature and form, custom and treaty often overlap in substance. But treaties can also crystallize emergent customs,³⁴ where crystallization means that the custom was in statu nascendi when the treaty was drafted but became a customary rule subsequently.³⁵ They can also generate custom, where a provision created in the process of the drafting of a treaty becomes customary because it is widely followed even by non-parties.³⁶

According to the ILC, all three types of treaties – those that codify custom, those that crystallize custom and those that generate custom – can be used in the process of CIL identification. Yet, as the ILC itself points out, a distinction needs to be drawn between the use of conduct in relation to treaties as state practice, where behaviour such as voting patterns is used as evidence for one of the elements of CIL, and the use of treaties as a reflection of CIL,³⁷ where actual treaty provisions are used as the container of a customary rule, because they have codified, crystallized or generated a customary rule.

The use of treaties for what is, or what in some cases the courts frame as, interpretation of customary rules in international courts and quasi-judicial bodies tends to fall into two categories: (1) the use of treaty provisions to interpret CIL; or (2) the use of elements from treaty interpretation to interpret CIL.

In none other than the Nicaragua case, where the ICJ established the relationship between treaties and custom, it also noted that ‘while the Court has no jurisdiction to consider that instrument [the Charter of the Organization of the American States] as applicable to the dispute, it may examine it to ascertain what light it throws on the content of customary international law’.³⁸ This statement was made in connection with the question of whether the lawful use by a third state of collective self-defence depended on a request from the attacked state.³⁹ After examining the provisions of the OAS Charter and the Inter-American Treaty of Reciprocal Assistance, the ICJ concluded that there was no rule allowing for the exercise of collective self-defence without a prior request made by the attacked state.⁴⁰ In this case, the court frames its reasoning as a form of interpretation. Yet, it ends up applying the requirement contained in the OAS Charter and the 1947 Rio Treaty, according to which the measures of collective self-defence must be taken at the request of the attacked state. This led to the following conclusion:

[T]he Court finds that in customary international law, whether of a general kind or that particular to the inter-American legal system, there is not rule permitting the exercise of collective self-defence in the absence of a request by the State which regards itself as the victim of the attack.⁴¹

In other words, the ICJ engaged in a form systemic integration as a gap-filling exercise bordering on law-making.

The second case under analysis is the Nuclear Weapons Advisory Opinion,⁴² which concerned the permissibility of the use and threat of use of nuclear weapons. The issue was controversial because international humanitarian law, including customary rules, lacked specific rules that would govern the use or threat of use of nuclear weapons in particular. One of the members of the bench, Judge Guillaume, appended a separate opinion, in which he stated that the rules of the jus ad bellum – in this particular case Article 51 of the UN Charter – could provide a clarification of the rules of the jus in bello.⁴³ To answer the question on the extent to which the use or threat of use of nuclear weapons was permitted in international law, Judge Guillaume, largely following the ideas set out in the main advisory opinion, emphasized that given the content of Article 51, according to which nothing shall impair a state’s right of self-defence, the use of nuclear weapons is allowed.⁴⁴

Judge Guillaume further opined that customary rules of humanitarian law must also be ‘completed by reference to the rules concerning the collateral damage which attacks on legitimate military objectives can cause to civilian populations’,⁴⁵ as contained in the Additional Protocol to the Geneva Conventions. Therefore, the only prohibition in customary humanitarian law was on the use of weapons that could not distinguish between civilian and military targets, which, according to the judge, was not necessarily the case with nuclear weapons.⁴⁶

In both cases there was a legal gap, which was resolved by what was framed as an interpretative exercise and which, if accepted as such, would fall under the third meaning of systemic interpretation outlined in Section 2. Whereas in the first case the customary rules on self-defence were completed with the requirement of a request on the basis of a reference to the OAS conventions, in the second case treaty rules were used to make the argument that rules of customary international law do not prohibit the use or threat of use of nuclear weapons. In both cases, the answer was sought outside CIL or its constituent elements – there was no mention of either state practice or opinio juris – instead, the reasoning was framed as an attempt at clarification or explanation, both of which are more akin to interpretation rather than orthodox ascertainment of customary rules. While in its draft conclusions the ILC established that treaties may ‘assist in collecting, synthesizing or interpreting practice relevant to the identification of customary international law, and may offer precise formulations to frame and guide an inquiry into its two constituent elements’,⁴⁷ it is clear that the function of treaties in these cases goes beyond this and extends to interpretation lato sensu of the content of CIL in a way that completes it.

Two other cases, both from the practice of international and internationalized criminal courts, show a different facet of systemic interpretation. In The Prosecutor v. Kunarac the Trial Chamber of the International Criminal Tribunal for the Former Yugoslavia (ICTY) sought to establish the definition of torture under customary international law.⁴⁸ After noting that the definition given in the Convention against Torture⁴⁹ could be taken as representing customary international law, the Trial Chamber stated that Article 1 of the Convention against Torture could nevertheless be used as an interpretational aid.⁵⁰ In a similar vein, in The Prosecutor v. Chea the Pre-Trial Chamber of the Extraordinary Chambers in the Courts of Cambodia (ECCC) found that the expression ‘other inhumane acts’ in connection with crimes against humanity was likely a CIL rule and then stated that:

in determining what constitutes ‘inhumane’ conduct reference could be made to: 1) serious breaches of international law regulating armed conflict from 1975–1979, including the grave breaches provisions of the 1949 Geneva Conventions or 2) serious violations of the fundamental human rights norms protected under international law at the relevant time.⁵¹

In these cases, other treaty provisions seem to have been used for construing the meaning of the customary rule, which comes closest to the first meaning of systemic interpretation described in Section 2.

Another pair of cases – or two individual opinions, to be more precise – illustrate how elements of treaty interpretation have been used in an interpretative argument on customary rules. The first example is the dissenting opinion of Judge Sørensen in the North Sea Continental Shelf case,⁵² where he noted that:

If the provisions of a given convention are recognized as generally accepted rules of law, this is likely to have an important bearing upon any problem of interpretation which may arise. In the absence of a convention of this nature, any question as to the exact scope and implications of a customary rule must be answered on the basis of a detailed analysis of the State practice out of which the customary rule has emerged. If, on the other hand, the provisions of the convention serve as evidence of generally accepted rules of law, it is legitimate, or even necessary, to have recourse to ordinary principles of treaty interpretation, including, if the circumstances so require, an examination of travaux préparatoires.⁵³

Unlike in the previous pair of cases, where treaties themselves were used to construe and complete the content of customary rules, in this case Judge Sørensen, while not actually making an interpretation on the basis of elements of treaty interpretation, clearly advocated in its favour, but only in cases where the treaty codifies, crystallizes or generates rules of CIL. In such a case, the argument goes, judges may resort to considering even the preparatory work of the treaty.

The second example is Judge Shahabudeen’s dissent from the Decision on Interlocutory Appeal from the ICTY in Hadžihasanović. In this case the tribunal was called upon to determine whether a superior could be punished under the principle of command responsibility for acts committed by subordinates prior to the assumption of command.⁵⁴ When determining the scope of action of the customary principle of command responsibility, Judge Shahabudeen argued that ‘any interpretation [of the customary rule] can be made by reference to the object and purpose of the provisions laying down the doctrine’⁵⁵ – Articles 86 and 87 of Protocol I Additional to the Geneva Conventions.

A final example that illustrates this approach is the judgment of the Appeals Chamber of the ICTY in The Prosecutor v. Aleksovski.⁵⁶ In examining the standard of control for the purposes of establishing the international character of an armed conflict, the Appeals Chamber opined that:

To the extent that it provides for greater protection of civilian victims of armed conflicts, this [the overall control test] different and less rigorous standard is wholly consistent with the fundamental purpose of Geneva Convention IV, which is to ensure ‘protection of civilians to the maximum extent possible’⁵⁷

In other words, the Appeals Chamber favoured the overall control test applied in The Prosecutor v. Tadić over the effective control test applied in Nicaragua and used the purpose of Geneva Convention IV as an argument to buttress its position.⁵⁸ This statement evokes, to some extent, Article 32 of the VCLT, according to which supplementary means of interpretation may be used to confirm the meaning arrived at through the general rule. However, it is not so much a supplementary means of interpretation, as foreseen in Article 32, but rather the consistency of the chosen standard with the purpose of a treaty that is being used here to confirm the choice in favour of the overall control standard. At the same time, the argument relies on the need to ensure normative harmony or consistency between the chosen standard and the convention in relation to which it applies. All in all, in terms of qualification, here it seems that the courts are engaged in an operation akin to that of systemic interpretation in its second meaning – as a tool for crafting systemic arguments.

4 Interpretation of Customary Rules by Reference to General Principles

While it seems that general principles have no role to play in the identification of CIL, in the practice of courts, especially criminal courts, it can be seen how the two can be embedded in judicial reasoning, often to the point of confusion. A few words, then, must first be said about the conceptual embeddedness and difference between general principles and custom.⁵⁹

References to principles in the case law of international courts frequently cause confusion because it is unclear whether they are referring to fundamental principles of international law or those belonging to a branch of international law or to general principles of law recognized by civilized nations.⁶⁰ The latter, in turn, may be variously defined as domestic law principles that are common to all/most States, such as estoppel;⁶¹ as natural law principles, such as equity or considerations of humanity;⁶² as principles that originate from international relations;⁶³ or as ‘general propositions underlying the various rules of law which express the essential qualities of juridical truth itself’.⁶⁴ Because of this lack of agreement or clear-cut definition of (general) principles, their analysis is often embedded with that of custom.⁶⁵ This is seen especially where ad hoc courts and tribunals declare their aim to be the establishment of customary international law at a particular point in time, whereas in actual fact they are surveying the domestic legislation of states, not as state practice but for the purpose of finding a common denominator in the definition of specific crimes.⁶⁶

The embeddedness between general principles and custom can be seen not only in case law but also in those writings of legal scholars that propound a broad understanding of the concept of customary international law.⁶⁷ The confusion is due to, or at least so it seems, the early practice of the Permanent Court of International Justice (PCIJ). For instance, in the Lotus case the PCIJ observed that ‘rules of law binding upon States therefore emanate from their own free will as expressed in conventions or by usages generally accepted as expressing principles of law’.⁶⁸ What adds to the confusion is that in its more recent practice, the ICJ seems to have requalified as CIL norms that it previously considered to be general principles.⁶⁹

The absence of a clear-cut distinction can even be found in the conclusions of the ILC. The ILC’s stance is that the ‘“rules” of customary international law … may be referred to as “principles” because of their more general and more fundamental character’.⁷⁰ In other words, it is admitted that general principles can be of a customary origin (also given that CIL is part and parcel of general international law) and are distinguished from regular customary rules by possessing a higher degree of abstractness.⁷¹ The practice of international courts and tribunals seems to support this view, at least to a certain degree.⁷² If, however, a neat distinction is maintained between general principles and CIL, then, given the former’s high degree of generality, general principles constitute a residual category, acting as a filler when the other two sources – treaties and CIL – are unable to resolve the dispute.⁷³

According to Judge Trindade of the ICJ, general principles of law ‘orient the interpretation and application of the norms and rules of this legal order, be they customary or conventional’.⁷⁴ The ICTY seems to share this view. In The Prosecutor v. Kupreškić,⁷⁵ the Trial Chamber, by taking into account other principles, expressed its clear support for a systemic approach when examining the prohibition of attacks on civilian populations. The Trial Chamber argued that to establish ‘the scope and purport’⁷⁶ of the customary rules on the requirement of proportionality between collateral damage and direct military advantage and the prohibition of the use of indiscriminate means or methods of warfare, it was necessary to interpret them by reference to elementary considerations of humanity, which the Trial Chamber framed as being ‘illustrative of a general principle of international law’.⁷⁷

In The Prosecutor v. Furundžija, the Trial Chamber had to decide on the definition of rape and the forms of behaviour that fell under this offence and, in particular, whether oral penetration could qualify as rape.⁷⁸ The Trial Chamber firstly stated that the prohibition of rape in armed conflict had evolved into a norm of customary international law,⁷⁹ yet found that international law (whether treaty or custom) contained no definition of rape.⁸⁰ Subsequently, it scrutinised national legislation and, as a result, established that while national laws generally converged around the definition of rape as ‘the forcible sexual penetration of the human body by the penis or the forcible insertion of any other object into either the vagina or the anus’,⁸¹ there were discrepancies concerning whether oral penetration qualified as rape or a different type of sexual assault.⁸² The question of whether the definition of rape included or excluded oral penetration was decided by reliance on the principle of respect for human dignity as ‘the essence of the whole corpus of international humanitarian law as well as human rights law’.⁸³ The inclusion of oral penetration in the definition of rape, both as a treaty and a customary prohibition, was preferred because this solution appeared to be ‘consonant with this principle’.⁸⁴ Judging from these two cases, it appears that general principles of law are used mainly for making systemic arguments that would determine the scope of the customary rule, thus falling under the second meaning of systemic interpretation.

An example of how the language of systemic interpretation can be misused is found in Case 002, where the ECCC Trial Chamber stated that ‘as recognised by the Pre-Trial Chamber, having regard to general principles of law can assist when defining the elements of an international crime, where that crime has otherwise been recognised in customary international law’.⁸⁵ After surveying the legislation of different countries, the Trial Chamber concluded that the mens rea of murder as a crime against humanity included dolus eventualis.⁸⁶ While announcing what appears a systemic approach towards the interpretation of the elements of the crimes found in CIL, the Pre-Trial Chamber ended up surveying the legislation of states and, given that the majority included dolus eventualis as the mental element for this crime, established that this had been the mens rea for murder prior to 1975.

5 Interpretation of Customary Rules by Reference to the System of Rules as a Whole

To complement the case law analysed in the previous sections, where other rules were used to construe custom, mention should lastly be made of a case where judges relied on a system of rules in its entirety to interpret the customary rule on attribution. In The Prosecutor v. Tadić, when arguing against the use of the Nicaragua effective control test in this case, the Appeals Chamber made the overarching argument that ‘a first ground on which the Nicaragua test as such may be held to be unconvincing is based on the very logic of the entire system of international law on State responsibility’.⁸⁷ It subsequently added that:

the whole body of international law on State responsibility is based on a realistic concept of accountability, which disregards legal formalities and aims at ensuring that States entrusting some functions to individuals or groups of individuals must answer for their actions, even when they act contrary to their directives.⁸⁸

In addition, it stated that the same logic had to apply to the questions on the appropriate control test.⁸⁹ Overall, when looking at the argument advanced by the Appeals Chamber, it appears to conflate teleological considerations with systemic ones in order to show why the effective control test is at odds with the whole system of state responsibility. In subsequent paragraphs, the Appeals Chamber examined state practice and opinio juris to show how the effective control was not rooted in practice.⁹⁰ However, this was done only subsequently and as an additional argument to the first teleological-systemic argument advanced, which means that it supports the argument being made here that ascertainment of state practice and opinio juris cannot be considered the only methods of determining the content of CIL rules in the case law of international courts and tribunals. This is an instance of a classic systemic argument in interpretation combined with teleological considerations, which shows that systemic arguments in the wider sense are not alien to the interpretation of customary rules.

6 Conclusion

Systemic treaty interpretation is ever-present in the practice of international courts and tribunals. While the term does not at first glance appear equivocal, it has in fact been used to refer to four different operations. Firstly, it may denote the act of using other rules as an aid to determine the meaning of treaty terms. Secondly, it can mean the use of systemic interpretative arguments. Thirdly, it has been used to refer to the act of gap-filling and, lastly, to the act of resolving conflicts between norms.

As this chapter has shown, systemic interpretation is also not foreign to CIL rules and, as with treaties, different variants of systemic interpretation have emerged in the practice of international courts. The most common is the use of systemic interpretative arguments, where other rules or the rules of the system taken as a whole are used to construe the content of a customary rule.

That systemic interpretation is equally capable of applying to customary rules not only advances our understanding of CIL interpretation but is further proof of the enduring interconnection between CIL and the two other sources of international law – treaties and general principles of law.

12 Reconciling Conflicting Norms of CIL Towards a Method of Practical Concordance at the ICJ

Raphael Oidtmann

1 Introduction

The risk of possibly conflicting norms of customary international law (CIL) has received increased attention in recent international legal scholarship and practice.¹ In the absence of commonly accepted or authoritative rules of conflict that may mitigate the ramifications which stem from a possible clash of opposing obligations under CIL, legal scholars and practitioners alike almost instinctively turn towards competent (judicial) authorities, thereby seeking advice on how to strike a balance between conflicting norms in conformity with applicable legal frameworks and regimes. The emergence of this ‘legal dilemma’ hence calls for, and even heralds, an established and accepted modus operandi to which international judges and adjudicators – as competent authorities – can resort in relevant situations. This basic constellation of juxtaposing norms pointing in different directions is of significant relevance, most importantly with regard to the operations of the International Court of Justice (ICJ), designated as ‘the principal judicial organ of the United Nations’² and competent to adjudicate on ‘any question of international law’.³

The tension inherent in the coincidence of contrary, yet equally valid and established, norms of CIL has hence become an increasingly real issue in recent years. For example, it arises in relation to the scope and application of ratione personae immunity from prosecution and adjudication enjoyed by heads of state, heads of government, and ministers of foreign affairs for international (core) crimes. The underlying conflict has become especially manifest in the Al Bashir⁴ case at the International Criminal Court (ICC). The case concerns acts committed by the former Sudanese president Omar Al Bashir, who has been charged with genocide, crimes against humanity, and war crimes in the context of the situation in Darfur – referred to the International Criminal Court by the United Nations (UN) Security Council under its Chapter VII powers⁵ – and is the subject of two arrest warrants issued in recent years.⁶ Beyond the question of Al Bashir’s imputed individual criminal responsibility for these international crimes, this case subsequently triggered a series of interrelated legal and legislative developments in a number of states parties to the Rome Statute⁷. Most importantly, they concerned constitutional issues flowing from the fact that Al Bashir had sojourned on the territory of states parties to the Rome Statute notwithstanding the pending arrest warrants and related legal obligations under the Statute.⁸ Accordingly, the case of Al Bashir has offered an enduring illustration of some of the inherent tensions that might arise between two possibly conflicting, yet imperative, norms of CIL:⁹ on the one hand, the established principle of ratione personae immunity applicable to heads of state, heads of government, and ministers of foreign affairs;¹⁰ and, on the other, the imperative to end impunity for international (core) crimes by facilitating individual criminal responsibility under international law.

This cursory sketch of two CIL norms in possible conflict with one another points, however, to a more structural tension – namely the question of applying and reconciling (seemingly) opposing legal principles in concrete circumstances. Thus far, international courts and tribunals, including the ICJ, have regularly refrained from outlining, conceiving, and imposing coherent analytical and prescriptive means of establishing an equilibrium between (partially) opposing norms of CIL in situ. Yet, devising such means – i.e. the creating transparent and selective rules of collision – could arguably assist international judges in striking a reasonable and credible balance in reconciling conflicting norms of CIL in concrete cases. In this chapter it is submitted that in such circumstances international adjudicative bodies could contemplate resorting to the German constitutional law principle of practical concordance (praktische Konkordanz) and thereby draw on a legal methodology that has become well established and is regularly applied by the German Federal Constitutional Court when ruling on fundamental rights.¹¹ The principle is applied in cases where there is a conflict between fundamental norms of equal (constitutional) rank, neither of which can be fully or partially overridden.¹² A core objective of practical concordance is thus the careful balancing of the two legal norms so as to allow each to be as fully effective as possible. Given that any legal arrangement needs to be assessed in context, practical concordance denotes essentially both a relationship of qualified precedence and a method of resolving conflicting legal standards – that is, establishing a specific rule of conflict in situ.

This chapter’s objective is threefold. Firstly, it discusses an example of a dichotomous conflict of CIL norms – namely, between the rule on immunity ratione personae and the rule on individual criminal responsibility. Secondly, the notion of practical concordance is introduced and then (re-)conceptualized as a form of an adjudicative reasoning that international courts and tribunals, including the ICJ, can apply to (better) address situations in which there is a potential conflict between CIL norms. Thirdly, the chapter will offer some tentative thoughts on how to address possible ramifications arising for international judges called upon to adjudicate in cases where such conflicts occur and thereby outline how practical concordance might assist in addressing underlying legal dilemmas.

2 The Interplay between Personal Immunity and Individual Criminal Responsibility

There has been much scholarly debate around the controversial question of immunity ratione personae, or personal immunity from criminal jurisdiction. It appears to be a well-established principle of CIL that heads of state, heads of government, and foreign ministers are considered to enjoy extensive immunity as individuals during their time in office, such immunity covering both private and official conduct.¹³ It implies that since these officeholders represent and even incarnate the state throughout their tenure, any affront to their dignity and inviolability should, by extension, amount to an affront to the state they represent.¹⁴

This understanding of immunity ratione personae was confirmed the International Court of Justice in the Armed Activities case, affirming that ‘it is a well-established rule of international law that the Head of State, the Head of Government and the Minister for Foreign Affairs are deemed to represent the State merely by virtue of exercising their functions, including for the performance, on behalf of the said State, of unilateral acts having the force of international commitments’.¹⁵ Further substantiation of immunity ratione personae for heads of state as CIL can be found in the Vienna Convention on the Law of Treaties.¹⁶ Codifying pre-existing CIL,¹⁷ the Convention states: ‘In virtue of their function and without having to produce full powers, the following are considered as representing their State: (a) Heads of State, Heads of Government and Foreign Ministers, for the purpose of performing all acts relating to the conclusion of a treaty.’¹⁸

The notion of immunity ratione personae under CIL becomes particularly relevant in matters concerning international criminal justice and related questions of jurisdiction. In the Arrest Warrant case, the ICJ examined whether individuals entitled to personal immunity might be charged and subsequently prosecuted in domestic courts for having allegedly committed international crimes. It clarified that ‘in international law it is firmly established that … certain holders of high-ranking office in a State, such as the Head of State, Head of Government and Minister for Foreign Affairs, enjoy immunities from jurisdiction in other States, both civil and criminal’.¹⁹ As far as criminal proceedings before foreign courts were concerned, however, the court underlined that foreign affairs ministers would enjoy full and unlimited ratione personae immunity, elaborating that:

throughout the duration of his or her office, he or she when abroad enjoys full immunity from criminal jurisdiction and inviolability …

In this respect, no distinction can be drawn between acts performed by a Minister of Foreign Affairs in an ‘official’ capacity, and those claimed to have been performed in a ‘private capacity’, or, for that matter, between acts performed before the person concerned assumed office as Minister for Foreign Affairs and acts committed during the period in office.²⁰

Confirming and further substantiating the applicability of immunity ratione personae in proceedings before domestic courts, the ICJ acknowledged and, moreover, clarified in what circumstances the personal immunity enjoyed by an officeholder would not preclude criminal prosecution. This would be the case if the proceedings took place in their home country, or if the home state decided to waive their immunity. Beyond that, once an individual ceased to hold office, they would no longer enjoy the privileges and immunities accorded by international law in third states. Thus, provided it had jurisdiction under international law, a foreign court could try a former foreign affairs minister of another state for acts allegedly committed prior to or after their term in office, as well as for acts alleged to have been committed in a private capacity during the minister’s term in office.²¹

In an obiter dictum, the court pointed out that both incumbent and former foreign affairs ministers could be pursued in criminal proceedings before ‘certain international criminal courts, where they have jurisdiction’.²² In particular, this would apply to the International Criminal Tribunal for the Former Yugoslavia, the International Criminal Tribunal for Rwanda,²³ and – though still in the process of being created at the time the judgment was rendered – the International Criminal Court. It was also noted that the latter’s founding legal document, the Rome Statute, expressly provided that: ‘Immunities or special procedural rules which may attach to the official capacity of a person, whether under national or international law, shall not bar the Court from exercising its jurisdiction over such a person.’²⁴ Although this differentiation in the application of ratione personae immunity between the international and domestic spheres expressed in an obiter dictum was not unequivocally endorsed by the entire bench,²⁵ the judgment pointed to a tacit consensus in statu nascendi, according to which certain and future international criminal courts and tribunals with the necessary jurisdiction over international core crimes might indict and prosecute both incumbent and former holders of the highest offices of state. Accordingly, the ratione personae immunity to which such individuals would otherwise be entitled in connection with such offences would no longer apply.

As a relatively new development, this re-configuration of the legal and conceptual understanding of the role and functions of ratione personae immunity under (customary) international law has become the object of increasingly close scholarly scrutiny in recent years, particularly in relation to heads of state. Historically, heads of state have been seen as enjoying considerably broad, if not absolute, immunity from foreign jurisdiction – in part, reflecting and reinforcing the prevailing belief in states’ sovereign immunity. However, a tangible decline in the deference paid to incumbents of highest state offices and the concomitant replacement of the former absolute immunity by a more qualified and conditional approach towards immunity, as well as an increasing emphasis on functional rather than personal status as the referential frame for according immunity, have, in sum, led to the above-described legal and conceptual re-alignment. As a result, ratione personae immunity for heads of states is now scrutinized in a far more critical manner. That said, the degree and extent of this change, and thus of the re-conceptualization of the scope of ratione personae immunity in respect of both substance and application have remained rather unclear.²⁶ This may in part be due to the fact that the legal construct of ratione personae immunity resembles a sui generis phenomenon: accordingly, analogies with the legal categorization of other state offices – such as, most importantly, diplomatic agents – are far from ideal, as they do not fully account for the specificities of personal immunity. Given that only a few international courts have thus far addressed the jurisdictional implications of ratione personae immunity in a comprehensive and authoritative manner, its legal status – both internationally and in domestic contexts – is still being dealt with primarily as a matter of CIL.²⁷ Thus, while neighbouring foundational principles of international law, such as the sovereign equality of states or sovereign immunity, are clearly helpful in delineating the scope and nature of immunities ratione personae, those principles are insufficient to arrive at a comprehensive and contemporary determination of the formers’ status under CIL.

The last twenty-five years have thus seen growing unease in international legal scholarship over unconditionally according almost unlimited personal immunity, given the emergence of an array of international crimes and the growing number of capable international adjudicative bodies having jurisdiction to rule on them.²⁸ The concern to guarantee human rights protection has led to increasing deliberation on the possibility of legally challenging the conduct of heads of state, heads of government, and ministers of foreign affairs, including, in a limited number of cases, also in the courts of foreign states and, in particular, in a growing number of international criminal courts and tribunals, with a view to possibly overriding the previously accepted conceptualization of personal immunity conferred on those selected individuals under CIL.

Assuming that immunity for heads of state, heads of government, and ministers of foreign affairs is still – notwithstanding the aforementioned efforts, most notably on the part of the International Law Commission,²⁹ to codify it – primarily based on CIL, no clear indication has been given as to how this principle may be properly reconciled with other, potentially conflicting customary norms that have the same legal rank. This is most importantly the case when the principle of ratione personae immunity comes up against that of individual criminal responsibility, aimed at ending impunity for international core crimes. This latter principle has two fundamental dimensions: firstly, it confirms that individuals can be held accountable directly under international law for certain criminal offences, thereby becoming subjects of international law and bypassing the state as an intermediary. Secondly, it implies that individuals may incur personal culpability for these specific offences and can therefore be held accountable for their conduct within the international arena.

Outside the laws of war – in which context individual combatants, are to be held liable, albeit to a limited degree, in the case of violations of international humanitarian law in their home jurisdictions – individual criminal responsibility has been recognized under CIL for offences such as piracy, crimes against peace, and crimes against humanity, and has subsequently been affirmed for other kinds of crimes in various international treaties that address the protection of human rights, both in times of war and peace.³⁰ Conversely, certain international crimes that have been codified in international treaties are considered to have (subsequently) entered the corpus of CIL – for example, the crime of genocide.³¹

Individual criminal responsibility as a norm of CIL has its foundations in the so-called Nuremberg Principles, espoused in the wake of World War II. On 11 December 1946, the United Nations General Assembly unanimously adopted Resolution 95(I),³² in which it ‘[a]ffirms the principles of international law recognized by the Charter of the Nuremberg Tribunal and the judgment of the Tribunal’.³³ Simultaneously, the General Assembly instructed the body that later became known as the International Law Commission to draft guiding principles essentially reflecting the Nuremberg and Tokyo Charters’ foundational provisions and the jurisdictional mandates of their respective tribunals. During the ILC’s deliberations, the question of the need to determine whether the rules applied by both adjudicative bodies already constituted applicable principles of international law arose. Given that this was the interpretation of the UN General Assembly in its Resolution 95(I), the legal nature of the principles was considered sufficiently established. During the following years, a growing number of domestic criminal courts of different kinds referred to the Nuremberg Principles, thereby endorsing and accepting their nature and scope as general principles of (international) criminal law. For example, in the Eichmann case, the District Court of Jerusalem emphasised that Resolution 95(I) showed the Nuremberg Principles to be part of CIL.³⁴ Following similar reasoning, the International Criminal Tribunal for the Former Yugoslavia confirmed the overall customary law status of individual criminal responsibility in Tadić.³⁵

The notion of individual criminal responsibility therefore lies at the very core of the international criminal justice system. However, it increasingly depends upon interactions with cognate legal concepts and other sub-realms of international law. Therefore, how individual criminal responsibility develops in the future will be a function of related legal principles such as an (international) duty to prosecute for defined criminal offences; international legal rules on immunities and amnesties; and the likelihood of co-operation between international criminal courts and tribunals, domestic justice systems, and states more broadly. The actual extent to which individual criminal responsibility might thus (still) be evaded through the application of particular legal principles – such as ratione personae immunity – has therefore remained a controversial and steadily evolving phenomenon, featuring in an ever-increasing number of cases before international criminal courts and tribunals – for example, Taylor³⁶ and Kallon and Kamara³⁷ before the Special Court for Sierra Leone and Karadzic³⁸ before the International Criminal Tribunal for the Former Yugoslavia.

It is this complex legal entanglement that is at the root of the somewhat uneasy interplay and interdependence between ratione personae immunity and individual criminal responsibility as potentially conflicting CIL norms. As explained in Section 1, this predicament has been notably highlighted by the case of (former) Sudanese president Al Bashir and the charges brought against him before the International Criminal Court for his alleged role in the Darfur conflict.

3 Introduction of Practical Concordance into International Adjudication

The notion of practical concordance has its origin in German constitutional law; it can be thought of as a guiding (legal) principle and is particularly characteristic of human rights jurisprudence. Deriving from the Latin concodare (to agree), the principle of practical concordance is regularly applied as a means of arriving at a legal equilibrium in human rights cases in which there is a risk of conflict between constitutional norms of equal rank, neither of which should take precedence over the other and both of which call for protection. In relation to possibly conflicting constitutional principles, the intention is to strike a deliberate balance that allows both legal principles to produce their effects as harmoniously and fully as possible. Typically applied to concrete constitutional scenarios, in which possibly conflicting fundamental norms need to be reconciled, practical concordance is informed by case-specific logic, in which legal interests and preferences need to be interpreted in the light of other constitutional principles and purposes. It therefore represents a conditional and, possibly, temporary prioritisation between norms of equal constitutional rank. As a distinct method of reconciling conflicting constitutional norms by balancing them against one another and scrutinising them vis-à-vis other legal considerations, practical concordance can thus be conceived as a specific rule on collision. This is not to say, however, that practical concordance is to be applied unconditionally; it is not applicable in cases in which the legal norm in question might collide with higher-ranking or more specific norms, or in which the norm might contradict general legal norms and principles – the colliding norm would in such cases lie outside practical concordance’s scope of application.³⁹

The notion of practical concordance owes its place in the German constitutional law debate above all to the German academic Konrad Hesse, who defined the principle as a method according to which ‘[c]onstitutionally protected legal interests must be co-ordinated with each other in the solution in such a way that each of them becomes reality. … [L]imits must thus be set for both legal interests so that each may attain optimal effectiveness.⁴⁰ According to the definition provided by Hesse, the realization of one legal interest shall not be at the expense of the other, which also excludes an over-hasty weighing or accommodation of conflicting legal positions. In that sense, practical concordance is geared towards an overall imperative of constitutional unity and thus of both coherence and impartiality, the ultimate aim being to establish a lasting balance while at the same time furthering both legal interests at issue. In this respect, practical concordance could be considered an emanation of the principle of proportionality. Expressed differently, practical concordance realizes two seemingly different, yet inherently interlinked, objectives – namely, to reconcile conflicting norms through a harmonized interpretation and to facilitate an equilibrium among norms.

This explains the widespread attention and approval given to practical concordance in domestic constitutional debates in several (mostly German-speaking) countries. The principle is today generally recognized as a constitutionally grounded balancing mechanism between potentially conflicting legal norms, the aim of which is to achieve an equilibrium between those norms and thereby generate a state of practical concordance. The concrete scope and character of practical concordance has been delineated first and foremost by the German Federal Constitutional Court in its fundamental rights jurisprudence.⁴¹ In general, the principle serves in cases of collision between fundamental rights that are guaranteed without qualification and is thus applicable to a broad range of fundamental rights collisions and interrelated conflicting constitutional principles. It has been questioned, however, whether the factual application of practical concordance in the sense of a systemic method of interpretation can place limits (possibly unintended) on the protective scope normally inherent in an unconditionally guaranteed fundamental right. If the conflicting constitutional provision amounts to a limitation in itself, this may justify the imposition of limits, provided the norm collision concerned is addressed and balanced in the spirit of practical concordance. On this particular issue, constitutional jurisprudence has remained rather patchy.

The foundational idea on which practical concordance is grounded also constitutes the basis for what other constitutional scholars, such as Peter Lerche, have identified as the components of an appropriate balancing of conflicting, yet constitutionally protected and relevant, interests as a way of legitimizing contingent restrictions on fundamental rights.⁴² This approach lends itself to situations in which the absence of an explicit authorization to restrict fundamental rights may need to be compensated by imparting constitutional legitimation. The rationale implicitly underlying practical concordance has subsequently been adopted by constitutional orders outside Germany – for example, in France⁴³ and Switzerland,⁴⁴ where the notion has been taken up, sometimes unchanged, in both constitutional law scholarship and fundamental rights jurisprudence.

Although international law recognizes the existence of conflicting norms and provisions and has long-developed rules of conflict at its disposal, including general principles of law such as lex specialis derogat legi generali,⁴⁵ – the tension between conflicting CIL norms may lead to profound legal dilemmas when adjudicative bodies, including the ICJ, are confronted with such conflicts. As the corpus of international law expands and becomes more fragmented, this legal-theoretical problem is likely to have ramifications and repercussions in both scholarly discourse and judicial practice. In the absence of authoritative rules of conflict that address this enduring tension, practical concordance can be used by international judges, alongside existing methods of interpretation such as the principle of effectiveness, systemic integration, or the principle of harmonization,⁴⁶ as a distinct analytical lens through which they can balance conflicting legal norms instead of preferring one norm to another one.

Section 4, sketches a possible way of introducing practical concordance into the legal toolkit employed by judges of international courts, including the ICJ. This transposition exercise seeks not to delineate yet another legal-methodological concept that can be regularly applied in a formal manner but rather to draw intellectual inspiration from the principle of practical concordance. The aim is to provide a tangible dimension and a name to the dilemma of reconciling conflicting CIL norms. The exercise aspires to raise awareness of this distinctive quandary among adjudicators, with a view to contributing to their reasoning and encouraging reflection on possible ways of establishing an equilibrium of legal interests in the concrete cases they handle.

4 ‘What a Judge Gotta Do’: Thoughts on Reconciling Conflicting CIL Norms at the ICJ

So, how can the judges of international adjudicative bodies make use of practical concordance in their daily work on the bench, and in particular at the ICJ? This section will propose various adjudicative ‘lenses’ whereby practical concordance might possibly contribute towards a more comprehensive assessment.

In recent years, international judges have increasingly become an object of research in themselves for international legal scholars.⁴⁷ Matters such as (legal) socialization⁴⁸ or international judges’ role in constituting court authority⁴⁹ have featured extensively in recent academic writings. These studies have shown that international judges carry with them an individualized legal fingerprint and trajectory, which determines the (legal) reasoning they pursue in any given case before them. Recalling that the principle of practical concordance has its origins in German constitutional law – and has thus far been mostly restricted thereto – it is no surprise that the concept has not (yet) expanded more broadly across international legal scholarship and penetrated the everyday practice of international judges.⁵⁰ Mindful of this caveat, the following thoughts are but a tentative and initial attempt to introduce the notion of practical concordance into contemporary international legal thinking.

In brief, practical concordance may fulfil a threefold function for international judges called upon to reconcile conflicting CIL norms. Firstly, it may serve as a methodological-analytical prism through which the customary norm(s) in question may be viewed, scrutinized, and de-constructed while being mindful of the need to achieve an equilibrium of norms. This implies that the substantive scope of each norm will necessarily be circumscribed. It could be said that this readiness to engage in a balancing process requires a mindset similar to that displayed when judges rule ex aequo et bono.

Secondly, although the above-mentioned equilibrium of norms is to be sought in situ – that is, pursued by international judges in the concrete cases before them – applying practical concordance at the same time requires the broader picture to be taken into consideration – that is, international judges must ponder the results of weighing different norms against one another and take account of the legal effects that might result across various (sub-)branches of international law. This applies particularly to the ICJ, which, as the ‘principal judicial organ of the United Nations’⁵¹ is of fundamental significance in the future development and practice of international law. With each decision they render, the ICJ judges address not only the legal interests at issue in the case before them but also the repercussions this may have for the domain of international law more broadly. Practical concordance could be regarded as a further aid in performing this role, accommodating international judges’ dual role as, on the one hand, authoritative arbitrators and legal interpreters in any given case before them and, on the other hand, international legal norm entrepreneurs, entrusted with developing international law in accordance with a constantly changing legal-political environment.

Thirdly, the application of practical concordance both enables and obliges international judges to take a ‘think outside the box’ approach when addressing legal dilemmas arising from the concurrence of possibly conflicting CIL norms and thereby to engage in judicial creativity. When applied in a given case, practical concordance requires established norms of (customary) international law to be balanced against one another in order to find an equitable solution to a previously disregarded legal dilemma. For this, interdisciplinary thinking and unorthodox legal approaches are needed. It also offers a way of upholding past precedence while striving for de lege ferenda.

Practical concordance should not therefore be regarded as a sophisticated and novel concept in legal theory. Rather, it denotes a distinct methodological lens through which cases that deal with conflicting CIL norms may be viewed, analysed, and resolved – hence putting a strong emphasis on considerations of balancing and compensation. Whether, to what extent, and in what way practical concordance may make inroads into the practices of international courts, especially the ICJ, remains to be seen. The compensatory character of practical concordance, which seeks an accommodation between prima facie contradictory CIL norms could emerge as a potential game-changer particularly whenever the ICJ is called upon to provide advisory opinions. It could, for example, help in answering the question of how to reconcile the ratione personae immunity enjoyed by heads of state, heads of government, and ministers of foreign affairs under international law with the pursuit of individual criminal accountability for international core crimes.

How, to what extent, and with what results might practical concordance be used by ICJ judges? While it might seem a somewhat vain exercise to ponder potential decisions in abstracto, and without wishing to interfere with judicial autonomy, a brief thought experiment will help to show how practical concordance could be applied to resolve conflicting CIL norms.

For this thought experiment, let us suppose that the ICJ is to render an advisory opinion at the request of the United Nations General Assembly⁵² on whether, how, and under what conditions two prima facie conflicting CIL norms–ratione personae immunity and individual criminal responsibility – may be reconciled. Our illustration will involve the (fictious) case of a sitting head of state accused of being responsible for an international crime falling within the jurisdiction of an international criminal tribunal legally empowered to adjudicate on such a situation. Faced with this (simplified) scenario, an international judge will need to take two initial steps. The first will be to analyse each (customary) norm and define its scope of application and the legal interests it protects, so as to distil the legal dilemma posed by the concurrence of the legal interests each norm seeks to protect. The second step will consist in delineating each norm’s legal nucleus – that is, the normative core to be preserved and without which the norm in question would become meaningless. This exercise will necessarily need to be placed within the context of the concrete case at hand and thus take account of the notional and circumstantial specifics of the case.

Taking this line of thinking a step further and applying it to the norms of ratione personae immunity and individual criminal responsibility, the establishment of an equilibrium between the norms would mean that neither norm is applied unrestrictedly, yet their overall applicability is upheld. As regards ratione personae immunity, this balancing could lead to confirmation that, for example, heads of state continue to enjoy extensive privileges, in particular before domestic courts, and that their previously unconditional immunity could be curtailed only where the individual is charged with a core crime of concern to the international community as a whole and this charge is made before a competent international criminal court or tribunal with the necessary jurisdiction. This qualified understanding of ratione personae immunity is the direct result of its being confronted with the other norm in question – namely, individual criminal responsibility. Although a bedrock principle in individualizing international justice, allowing the actual perpetrators of atrocious crimes (humans as opposed to states) to be held accountable, this principle would have to comport with the importance accorded to individuals who enjoy ratione personae immunity on account of their unique role as state representatives. For its part, therefore, the principle of individual criminal responsibility will have to be curtailed so that this limited circle of officeholders are prosecuted only before a competent international criminal court or tribunal with the necessary jurisdiction and only for a crime of concern to the international community as whole.

This (hypothetical) act of balancing can truly be considered an instance of practical concordance as the international judge will have engaged in a deliberate process of weighing both norms against one another and safeguarding each by ensuring that it remains intact and is not compromised or conceptually subordinated to the other. It should be pointed out that the balancing process could also lead to a different result, depending on the circumstances of the case. In our illustration, it can be claimed that both norms conserve their overall legitimacy and efficiency in protecting the fundamental legal interest(s) to which they relate and thus the substantive validity of those norms. In concreto, it would mean that a competent international criminal tribunal is required to prosecute a sitting head of state who enjoys ratione personae immunity save where that head of state is charged with crimes of concern to the international community as a whole. Although in this case the pendulum could be said to have swung more towards one of the two norms, the other norm’s overall applicability and validity in similar or different constellations is not undermined.

5 Conclusion

The present contribution has sought to introduce the notion of practical concordance into international adjudication and, in particular, into the everyday practice of international judges, thereby making the principle applicable in situations where possibly conflicting norms of CIL must be reconciled in situ. Far from a full-fledged legal-theoretical concept, practical concordance as presented here is rather a state of mind conducive to establishing an equilibrium between legal norms of equal rank and a distinct methodological approach in addressing legal dilemmas. It is hoped this contribution will spur further reflection on how to confront cases in which norms of CIL may conflict with one another, and thus point to the greater leverage offered by a more nuanced weighing of contradictory legal norms and principles.

13 Indicators of Coherence and the Interpretation of CIL

Charalampos Giannakopoulos

1 Introduction

Interpretation is ubiquitous in everyday life. We constantly interpret a variety of objects, including texts, signs, gestures, works of art, intentions, and human practices and interactions. Interpretation is central to the practice of international law, too. Arguing about international law’s content is the everyday business of international lawyers, and this often includes arguing about the existence and content of norms of customary international law (CIL). Although a number of scholars recognise that CIL can be interpreted,¹ disagreements remain as to the precise methods, modalities, and extent of CIL interpretation. Such disagreements are born of a common concern to secure competently made, coherent, and accurate interpretations of CIL, given the latter’s non-textual nature.

My aim in this chapter is to explore in a preliminary manner two related questions regarding CIL interpretation: (1) is it necessary, or even possible, to strive towards coherence in the interpretation of CIL? And (2) are there any possible indicators of (in-)coherence in that respect? Providing answers to these questions depends on how one understands coherence in the first place, including its relation to legal reasoning. A substantial part of the chapter will therefore deal with that as well.

Coherence is here envisaged as a state of axiological compatibility existing among a set of independent beliefs, statements, reasons for action, and so on, which are expressed at any level of abstraction. The degree of compatibility of the set is a function of the existence of internal structures of mutual, reciprocal support among the elements of the set, so that some of the elements are supported by other elements and vice versa.²

Based on this understanding, I make three broad claims. First, coherence is related to, yet still independent of, concepts like consistency, correctness, and comprehensiveness (and its corollary, predictability); and, moreover, it has two dimensions (one substantive, the other methodological) which are both relevant in law (Section 2). Second, this makes coherence particularly relevant to legal reasoning, where its dual dimension translates into a similar dual role that is also at once substantive and methodological (Section 3). Given this, coherence in law is more than a simple goal or a results-oriented ideal. It is also a method of constructing one’s reasoning and of deliberating about one’s interpretative choices. It is therefore both possible and, indeed, necessary to strive for coherence in the interpretation of CIL if one wishes to claim authority for, and persuade others of, one’s interpretation. Third, striving for coherence in the interpretation of CIL means being cognisant of three kinds of processes – namely, framing, contextualising, and iteration/reflexivity (Section 4). These can serve as indicators of (in-)coherent interpretations; however, they themselves are interpretative in nature and therefore can be subject to debate and reasonable disagreement.

2 The Independent Concept of Coherence

We tend to place value on coherence because it implies that something, or someone, makes sense and is intelligible. Being incoherent, by contrast, causes frustration and confusion. Coherence is thought to be a desirable attribute to have in virtually every aspect of one’s life. The legal field is no exception, where there exists a vast literature on coherence in law in general and a large consensus that coherence suits law and legal reasoning particularly well.³ However, coherence remains a largely under-theorised concept in the field of international law. One can, for example, find passing references to coherence in the ILC’s work on the fragmentation of international law. Therein, the ILC indicates that there exists a link between coherence and the principle of systemic integration under Article 31(3)(c) of the Vienna Convention on the Law of Treaties (VCLT).⁴ Beyond that, however, coherence seems to be generally regarded by the ILC as co-terminous with mere legal security and predictability, which is to say it is seen as a formal principle devoid of its own independent content.⁵ One sees a similar picture in other areas of international law, notably international investment law, where concerns of incoherence in arbitral awards have been raised for years alongside concerns about a perceived lack of judicial consistency, correctness, and predictability.⁶ Here, too, coherence is regarded as valuable, yet the content given to it is often interchangeable with that of legal certainty, predictability, and legal authority.⁷

Therefore, before we can ponder the role of coherence in interpreting CIL, one key question must be answered: what is coherence and what is its role in legal reasoning more generally? This section seeks to answer the first half of that question (what is coherence?) by demarcating coherence’s scope from other, related concepts like legal consistency, correctness, and comprehensiveness (and its corollary predictability).⁸ The goal is not simply to reduce confusion by disentangling the meaning of concepts but also to set proper expectations of the concept of coherence in the process. The second half of the question (the role of coherence in legal reasoning) is dealt with in Section 3.

2.1 Coherence and Consistency in Law

Consistency means absence of contradiction.⁹ Propositions are consistent if each can without contradiction be asserted in conjunction with every other proposition in the same set, and with their conjunction.¹⁰ Consistency is thus an absolute and logical property: any two propositions either are or are not consistent. By contrast, the conditions of satisfaction of coherence are less precise. The quality of being coherent is often conveyed through mental images and metaphors.¹¹ It is often said, for instance, that something is coherent if it hangs together well, if its parts fit and are mutually supportive, if it is intelligible, if it flows from or expresses a unified viewpoint; whereas the same thing would be incoherent if it is unintelligible, fragmented, or disjointed.¹² More generally, an attribute of coherence is that the object of enquiry ‘makes sense’, whereas an attribute of incoherence is that it does not.¹³

Neil MacCormick once used the following humorous example to make the distinction between consistency and coherence stand out more clearly. MacCormick asks us to imagine a house where the cleaning rules are as follows: leave everything as untidy as possible on Mondays, Wednesdays, and Fridays, but tidy everything up to the highest perfection on Tuesdays, Thursdays, and Saturdays (Sundays are reserved for resting). These rules can be easily observed, in the sense that none infringes upon the other, but they surely give rise to an unreasonable, indeed absurd, way of living, since they do not seem to serve any immediately discernible end – in short, they make no sense. The image of coherence painted by this example, and the general descriptions above, is that of a network – an interdependent web – between propositions and their justification standing or falling together.¹⁴

Transposed to law, it is therefore possible to restate the quality of being coherent – that is, a function of the ability to ‘make sense’ – as the degree to which a set of propositions are rationally related to each other and to the ordering values or principles that are thought to justify them – which MacCormick usefully summarised in the pithy phrase ‘axiological compatibility among two or more rules, all being justifiable by reference to some common principle or value’.¹⁵

Aiming for axiological compatibility involves a conscious effort to bring two or more propositions into accord with each other. As such, coherence is not an absolute property but rather a matter of degree and interpretation. Whereas consistency ‘is or is not’, coherence can be ‘more or less’. In the same vein, unlike coherence, consistency as a logical property remains agnostic towards the merits of the positions that are made consistent.¹⁶ Thus, ironically, greater consistency may actually perpetuate injustice. It follows that between consistency and coherence, consistency is the subordinate and dependent concept. For example, a perceived inconsistency between two judicial decisions may be interpreted away if one goes higher in the level of abstraction and considers the more general norms, principles, or values that have justified them. By the same token, two legal positions that appear consistent because they yield the same outcome may still not cohere if one looks at the norms, principles, or values that have justified them.

2.2 Coherence and Correctness in Law

Unlike coherence and consistency, coherence and correctness in law are generally not conflated with each other at a conceptual level or treated as interchangeable. However, because coherence is not agnostic towards the merits of the propositions that are made coherent, it is sometimes proposed that a requirement associated with coherence is the ability to arrive at right answers. That is to say, it is sometimes proposed that a coherent whole should be able to determine the single correct outcome in particular cases.¹⁷ However, this is not precisely the case, and the statement thus requires more nuance so as to avoid introducing distorting expectations of coherence. While there exists correlation between coherence and correctness, it is doubtful that this extends to causation. To see why, we must further distinguish between determinate and demonstrable correctness.

Something is determinately correct when the reasons offered in its support compel it, which is to say when they carry the greatest weight out of all other competing, plausible reasons supporting it.¹⁸ Determinate correctness is an instance of so-called ontological objectivity, which seeks to describe the way things are – their nature and existence – in this case by making particular reference to their ability to produce accurate answers.¹⁹ By contrast, something is demonstrably correct when its determinate, or at least plausible, correctness can be demonstrated to the satisfaction of everyone, or virtually everyone. Demonstrable correctness is thus an instance of so-called epistemic objectivity, which refers to the state of rational agents having formed a justified belief regarding the correctness of the object in question.²⁰ Determinate and demonstrable correctness are not absolute properties, but matters of degree. The stronger the reasons offered in support of an outcome, the more they would determine that outcome and, by extension, the more likely it would be that others are persuaded of the outcome’s correctness.

The above applies to the legal field as well. Law has an arguable character, meaning that statements about its content are in reality arguments supported by reasons whose relative strength and manner of deployment can vary.²¹ Evaluating the force of competing legal arguments is bound to be a matter of degree and calls for the exercise of judgement.²² Correctness in law, therefore, cannot be simply reduced to a mere pronouncement (e.g. ‘the law demands x’, or ‘party A must bear liability’) but is rather a combination of the content of the pronouncement and the content and structure of the reasons offered in supporting it.²³ The quality of correctness in law is always determined and demonstrated relatively to a set of strung-together premises and assumptions acting as reasons favouring some outcomes or courses of action over others.

Because coherence is axiological compatibility with guiding norms, values, or principles, coherence is thus linked to legal correctness in the following manner. One person’s ‘correct’ interpretation or decision may still be thought to cohere better than another’s, given the justification offered for each interpretation or decision, and given the method used to arrive at them. In other words, the existence of a coherent process of reasoning would mean that its outcome has a claim to correctness, but also that such a claim would not be absolute since another person’s process of reasoning may have been performed better, thus making the latter person’s proposed outcome arguably more coherent and with a stronger claim to correctness.

It follows, then, that coherence and correctness in law are not necessarily equivalent properties. An otherwise coherent process of justification may still result in an outcome which we may regard as legally incorrect for being in tension with collective attitudes and beliefs. One may use an appropriate method and link together the various aspects of the legal system in a competent manner (e.g. by properly identifying the relevant materials, legal norms, or past practices) but may nonetheless make a substantive, value-laden interpretation of them, with which at least some participants in the legal system may not agree. By the same token, determining that an outcome is coherent cannot be exclusively a function of the extent to which the decision is considered to be correct in its substance. One may reach a correct decision in substance, which everyone would agree that the law ought to provide, but do so through contradictory reasoning or through a not well-justified process, where the various elements of the legal system have not been linked together adequately or accurately. In such a case, we would be inclined to conclude that coherence is lacking, despite the moral appeal that the outcome itself may have.

2.3 Coherence and Comprehensiveness in Law

Yet a third requirement often associated with coherence is that of comprehensiveness, meaning the absence of gaps or uncertainties and the corresponding ability to readily supply an answer to each and every question that may be raised.²⁴ In the legal field, comprehensiveness can be linked to the value of predictability – that is, the ability of the law’s addressees to determine in advance the legal consequences of their actions. Comprehensiveness and predictability are properties that obtain in degrees. Enhancing comprehensiveness, in the sense of expanding the range of readily available answers to distinct questions of law, can result in greater predictability for the legal system’s addressees.

It may be a reasonable assumption to make that if a legal system is sufficiently comprehensive and thus exhibits a high degree of predictability, then it would also be coherent. However, it can be doubted whether such a connection would necessarily exist. Comprehensiveness does seem to improve the chances of overall coherence but probably cannot guarantee it, and, conversely, coherence does seem to improve the chances of eventually experiencing comprehensiveness over time (and hence predictability) but probably cannot guarantee that either.²⁵ As was the case with correctness previously, correlation does not equal causation.

The above conclusions follow logically from the previous examination of the links between coherence, consistency, and correctness. Because coherence is characterised by axiological compatibility, as opposed to mere non-contradiction, the predictability that would normally result from a nominally consistent line of interpretations or applications of the law does not mean that these would necessarily exhibit coherence also. Furthermore, one need not be fully comprehensive in scope, or perfectly predictable at the outset, to be coherent. This again applies especially in law, considering the well-recognised need for change and progressive development following the occurrence of novel situations not covered in existing legal instruments or following a change in collective attitudes and beliefs. By the same token, the inverse also holds true. Coherence does not preclude the need at times to strike a different path from what past consistent practice may indicate. Nor does coherence preclude the existence of gaps in the law.

2.4 Summing-up

How do consistency, correctness, and comprehensiveness fare as determinants of coherence? In the abstract, one may be inclined to say that the occurrence of all three is necessary to describe an object of study as coherent in ideal theory. Thus, the perfect co-existence of all three elements will necessarily render the object of study perfectly coherent in an ideal situation. Conversely, the absence of all three elements would render the object incoherent. However, based on the preceding analysis, the same conclusion does not seem to follow in practical, non-ideal situations. Indeed, three general points can be made in this respect.

First, although certainly desirable for coherence to exist, consistency is not a necessary or sufficient requirement of it. The presence or absence of consistency does not necessarily mean that coherence obtains or that coherence is forfeit. In fact, consistency seems to be the dependent concept when seen against coherence. Often, it is a sense of coherence that makes us either disregard contradictions as being only apparent (and thus capable of being interpreted away) or, indeed, call them out as being true.²⁶

Second, correctness is likewise not a necessary determinant of coherence. Although there exists a correlation between legal correctness (both determinate and demonstrable) and coherence, this does not extend to causation, given the law’s arguable character and the scope within it for debate and reasonable disagreement. Legal pronouncements may not always be determinately correct, yet they could still exhibit congruence with some of the system’s principles or values and be supported by a competently drafted statement of reasons. Incoherence resulting from a complete disregard of a system’s norms, practices, and principles, or from a complete disregard of the ways of structuring and presenting legal arguments, are likely to be rare.

Third, the same considerations apply also with respect to comprehensiveness as a determinant of coherence. Some unpredictability resulting from an absence of comprehensiveness is not necessarily a sign of incoherence. The law is always a work-in-progress and unpredictable outcomes may be caused by legal actors using novel doctrines, arguments, or theories that are not yet settled or widely accepted in the current state of the discipline.

The above leads to the conclusion that coherence is an independent concept having its own content. Were it not, we could only perceive it to the extent, if any, that it entails or is entailed by consistency, correctness, and comprehensiveness. That is to say, the conclusion ‘coherent or incoherent’ would necessarily follow from any statement about the law, so long as we considered that statement to be consistent, correct, or comprehensive (predictable). However, this does not appear to be the case in practice. To the contrary, we are ultimately not precluded from perceiving coherence in practice or from debating about coherence meaningfully, even when some of the above-identified elements are satisfied to a lesser extent or even entirely missing.

In the same vein, striving for coherence in the determination and interpretation of CIL should not mean that consistency, correctness, or predictability will be necessary outcomes, although they may be probable and, indeed, highly hoped-for outcomes. Does this then make coherence practically irrelevant when engaging in CIL interpretation or, for that matter, in any form of legal reasoning? Section 3 argues that it does not.

3 Practical Legal Reasoning and the Dual Role of Coherence

Legal reasoning is the principal means through which lawyers argue about the existence and content of law. This makes it natural to enquire about the role that coherence may have to play therein. Yet, answering this question presupposes answering a more fundamental question first: what kind of reasoning is legal reasoning? There are two candidate-types to consider in this respect: the theoretical and the practical. A fundamental difference between the two relates to their respective conditions of validity and the outcomes that each type of reasoning seeks to achieve.

Starting from the proposition that, much like other kinds of normative reasoning, legal reasoning is practical rather than merely theoretical, this section argues that seeing legal reasoning as practical leads to the conclusion that coherence has a dual role to play therein, a role that is at once substantive and methodological. The section concludes by hinting at three interpretative processes acting as possible indicators of (in-)coherence in legal reasoning, termed ‘framing’, ‘contextualisation’, and ‘iteration’/‘reflexivity’. Their importance for the interpretation of CIL is subsequently examined in Section 4.

3.1 Theoretical versus Practical Reasoning

In theoretical argumentation, one adduces reasons for or against forming a belief about what is or is not the case in reality.²⁷ Theoretical reasoning is thus reasoning principally about questions of fact, explanation, and prediction.²⁸ As such, it has a backward-looking and a forward-looking dimension. It is backward-looking when it looks at events that have occurred and asks why or how they have occurred. It is forward-looking when it uses past observations and the rules of logic to attempt a true determination about what is going to happen in the future. Given its format and reliance on the rules of logic, theoretical reasoning can be challenged in two ways: first, substantively, when the premises used are not accurate, thus leading to a necessarily inaccurate outcome (inaccurate assessment or collection of data); or, second, formally, when the syllogism itself violates the rules of logical consequence or entailment (impermissible moves between otherwise accurate premises).

Practical reasoning is different. Practical reasoning is reasoning about what to do when faced with a problematic situation. As such, it does not stop at formulating an opinion or belief about what the case may be, as theoretical reasoning does, but continues until one commits to a course of action. Put differently, practical reasoning attaches to a project an actor has (be it a problem requiring solution or a goal to be achieved) and seeks to identify the course of action that would lead to the satisfactory completion of that project.²⁹ From this fundamental point, a number of key differences between theoretical and practical reasoning emerge.

First, whereas the ends in a theoretical inference are clearly defined and certain (i.e. ascertaining the truth of a proposition or accepting it as a matter of belief), this is not always the case in a practical inference. Indeed, when we contemplate possible courses of action in practice, we often come across phenomena like complexity, uncertainty, instability, uniqueness, or value-conflict.³⁰ In these situations the ends cannot always be taken as given – which is to say, without some prior attempt at ascertaining their desirability or appropriateness as ends to be achieved in the first place.³¹ Therefore, in resolving a practical problem, an actor must also deliberate in order to prioritise or reconcile competing ends, including also the requirements underpinning the available courses of action to meet these ends.³² Reconciling and prioritising may lead the actor to choose a different course of action and to even amend their original goal. Practical deliberation thus requires the actor to simultaneously determine how to do what seems like a good idea of doing as well as whether it really is a good idea to do it in the first place.³³

Second, because ends in practical contexts are not beyond challenge or amendment, rationality in practical reasoning is not based only on logical entailment (as in theoretical reasoning) but also on plausibility. This means that although the outcome of a properly conducted theoretical inference will be the same for everyone, this is not a guarantee in a practical inference.³⁴ Two actors may both reason correctly from a logical point of view but still arrive at different courses of action, since there may be multiple suitable ways to achieve the same intended goal. Accordingly, rationality in a practical inference is a function of the degree to which a desirable end x is achieved by a course of action y, subject to any competing or countervailing reasons for not doing y given the possible existence of an additional, also desirable, end z. By enlarging the scope of the debate in this manner, the rationality of a practical inference may be affirmed or challenged.³⁵

Third, because of the above characteristics, practical inferences can be challenged in three ways: first, substantively, when the premises used are not accurate; second, formally, when the inference itself violates the rules of logical consequence or entailment; or third, defeasibly, through the introduction of additional contexts to the enquiry that do not necessarily make existing premises inaccurate yet, on balance, render them inappropriate and replaceable by better premises.³⁶

3.2 Legal Reasoning as Practical Reasoning

Traditional depictions of legal reasoning in international legal academia have closely tracked the theoretical model of reasoning just described.³⁷ Legal reasoning is thus often depicted as a chain of logical deduction consisting of a syllogism of the form ‘if p then q’, where p stands for a proposition of law and q stands for the consequence that follows from it.³⁸ The reasoner’s role is to input the set of facts that match the applicable proposition of law in order to get the legally prescribed solution. The more difficult the case, the more complex the chain of reasoning. Although this picture of legal reasoning can be challenged for being outdated and overly formalistic, it remains the prevailing narrative when it comes to CIL. That is, in relation to CIL, the above picture is often reversed by saying that the reasoner’s task is to identify the rule of CIL that is hidden in the raw facts of state practice in a process of logical induction.³⁹ Thus, the fundamentally syllogistic ‘if p then q’ format of reasoning is retained.

However, although often presented outwardly as a chain of demonstrable theoretical reasoning, legal reasoning better fits the format of practical reasoning.⁴⁰ Indeed, legal reasoning exhibits the three main characteristics of practical reasoning identified previously.

In the first place, legal reasoning intends to lead to action and not simply to the formation of a belief about the way things are in the current state of the law. States typically invoke law and make arguments about the law to justify taking a course of action in the future, to justify having taken a course of action in the past, and to block other states’ justifications for following one course of action rather than another. Similarly, when seised of a case, international adjudicators do not simply declare the law in the abstract; they commit themselves to a course of action by handing down a decision in favour of a disputing party, which is tailored to the particular circumstances of the case presented before them.

In the second place, legal reasoning is a purposive activity. And yet, as the ILC has also affirmed, the law’s ends are not always clearly defined, indisputably certain, or entirely uniform.⁴¹ Take international investment law. The preambles of international investment agreements indicate that states enter into them for a variety of reasons, including, for instance, to protect their investors abroad, to stimulate investment flows in their territory, or to contribute to their economic development. The choice to give foreign investors access to investor-state dispute settlement has also been justified on multiple grounds, including as an additional incentive to invest in another country⁴² or as a way to depoliticise investment disputes by removing them from the domain of diplomatic protection.⁴³

The same considerations apply, arguably with greater force, in the case of CIL. As Gorobets points out, customary norms are community norms.⁴⁴ Therefore, even when it is a small group of states or, indeed, a single state that originally sparked the creation of a CIL norm (one can think of the 1945 Truman proclamation on the continental shelf here), these states may not be regarded as the norm’s authors in exactly the same way as the contracting parties to a treaty are that treaty’s authors.⁴⁵ The juridical goals of the original ‘creators’ of a CIL norm are not immune from re-appraisal and re-interpretation by all subsequent actors who may seek to invoke and apply that norm in practice.

The conclusion would not be different even if one were to focus on purely doctrinal goals associated with the law – such as ensuring legal certainty, justice, or the rule of law – and sought to determine how these should be promoted through legal reasoning. We would still need to perform an act of interpretation of these abstract goals case by case, in light of the institutional role of the international actor who advances the legal argument in each instance. In short, interpretability of ends appears to be a ubiquitous feature of legal reasoning.

In the third place, legal reasoning is defeasible. Some legal questions can be genuinely difficult to answer. People who are competent and well informed about the law can still reasonably disagree about its content, despite starting from similar premises and advancing formally valid syllogisms. When lawyers disagree, they do so not only by challenging the accuracy of each other’s chosen premises or the logical consequence of their syllogism, but also by pointing out missing premises or missing contexts in a competing argument, which may render that argument less plausible or convincing.⁴⁶

3.3 A Dual Role for Coherence

To recap, legal reasoning is practical in the sense that it seeks to motivate a situated actor, who has certain goals, into committing to a particular course of action. In practical reasoning, an interactive and iterative relationship exists between the actor’s goals, the course of action chosen, and the mental steps taken in between – all these are, moreover, open to deliberation and modification in the course of reasoning. Thus understood, legal reasoning exhibits important coherence-related features. Because it is practical, legal reasoning spans out in a web of clustering reasons for action, rather than extending linearly as a chain. Moreover, by having interpretable goals, legal reasoning relies on axiological compatibility between these goals, the reasons that justify pursuing them, and the appropriateness of the steps taken to achieve them in practice. In other words, like practical reasoning, legal reasoning is meant to lead one to a conclusion about what ought to be done (or not done) given one’s evaluation of a problematic situation to be resolved or a goal to be achieved. The strength of a legal argument thus comes principally from the force of the connection – the degree of mutual supportiveness – between these various clusters of reasons.⁴⁷ The latter, in turn, is a function not only of the desirability of the reasons used but also of the way in which these reasons have been structured and made to interact in pursuit of the chosen goal.

What role, then, does coherence play in legal reasoning? I believe it plays a dual role, which is at once substantive and methodological. On the one hand, when faced with a legal problem, one must frame the legal question at issue; identify the normative context, including the governing values, principles, and other norms of conduct, that will guide the decision-making process; and, in so doing, also reflect on one’s institutional role and aims (including on their limits) in the legal system. Coherence here implies an overall congruence with the body of knowledge and value prevalent in the legal system in question,⁴⁸ and thus operates in a clearly normative way as a substantive principle. It assists in formulating, even if in the abstract, the end, purpose, or state of affairs to be achieved and the reasons supporting it in principle.

On the other hand, having come up with the end, purpose, or state of affairs to be achieved, one must then proceed by following an iterative process whereby one identifies concrete courses of action to fit the chosen end, purpose, or state of affairs; considers the impact on the identified actions of any countervailing ends, purposes, or states of affairs; in the process potentially reassesses the desirability of the end, purpose, or state of affairs originally chosen; and, if so, reformulates amended courses of action, as appropriate, to fit the reassessed end, purpose, or state of affairs to be achieved. The idea of coherence here takes on a methodological hue. It describes a reflexive process of internal deliberation and a manner of structuring all relevant elements into a justifying narrative that seems at least plausible, if not compelling, to the community at large.

Singled out from the above are three mental processes associated with coherence in law as potential indicators: (1) acts of framing, (2) acts of contextualising, and (3) acts of iteration/reflexivity. Section 4 offers some preliminary thoughts on how these three processes may fit within the interpretation of CIL.

4 Indicators of (In-)Coherence and the Interpretation of CIL

There exists a link between coherence’s dual role in legal reasoning and the interpretation of CIL. In particular, the three interpretative processes of framing, contextualising, and reflecting can act as indicators of the coherence or incoherence of one’s proposed interpretation of a CIL norm. The word ‘indicators’ is key, however, as it points to something less than a determinative test. Indeed, it is argued here that acts of framing, contextualising, and reflecting are themselves interpretative in nature and their successful deployment can therefore be the subject of debate and reasonable disagreement. Moreover, my listing of the three processes in the above manner does not mean to indicate a strict separation between them or their strictly sequential application in practice. Rather, I see these processes as three interdependent facets of the same interpretative operation.

An additional clarification must also be offered before proceeding. Perhaps unsurprisingly, the very term ‘interpretation’ can itself be subject to interpretation and to different understandings in different fields. In a broad sense, any act of apprehension of meaning and any ‘reading’ of a situation, no matter how commonplace, intuitive, or unmediated, can be said to involve interpretation.⁴⁹ This is not the common understanding of interpretation in international law. Interpretation in the latter is often understood in a narrower sense predicated on the existence of doubt about the meaning or the proper application of a pre-existing rule.⁵⁰ In this narrower sense, CIL interpretation can be seen as taking place only after a CIL rule has been identified;⁵¹ whereas the broader sense would see interpretation as permeating the entire lifecycle of CIL, from its formation and identification to the apprehension of its meaning now and in the future. The latter approach thus leaves open the interesting, but still somewhat controversial, possibility of state practice being a subject of interpretation also.⁵²

In what follows, I have in mind the broader sense of interpretation just identified. I understand interpretation as elucidating the content of legal norms, but also as a reasoned ‘reading’ of a situation populating it with meaning. I recognise that my use of the term has implications about the way one understands the concept of law itself. However, I will not offer any arguments on that here, nor, more generally, on the plausibility of shifting to an interpretative conception of international law.⁵³

4.1 Framing

Practice is the foundation of CIL’s existence and content: it is practice that becomes law if it is accepted as such by states.⁵⁴ Yet, identifying the elements of practice to figure into one’s ascertainment or interpretation of a CIL norm does not proceed on a blank slate. Rather, it presupposes a prior framing of a legal question in need of an answer, or of a problematic situation in need of resolution, forming the contours of a ‘project’ that the interpreter intends to complete as their legal goal.⁵⁵ The ‘project’, appropriately framed, helps to kick-start and guide the enquiry methodologically as well as substantively.⁵⁶ Thus understood, acts of framing are interpretative in at least three ways.

In the first place, framing helps to formulate legally acceptable goals to be achieved through the ascertainment of the content of a CIL norm. As Hakimi points out, international actors do not approach CIL as detached observers, but rather as ‘advocates advancing their own preferences’.⁵⁷ An understanding of the interpreter’s institutional role is therefore important. Different international actors have different institutional roles, affecting the kind of questions that can be asked, the legal problems that need resolving, or the arguments that can be made. For instance, states enjoy greater freedom in devising policy goals to be pursued through legal means. States can thus generate arguments about possible new CIL norms, or about new meanings to be assigned to existing CIL norms, simply by acting and by justifying such action against existing practice or against their reasoned views about the action’s appropriateness or desirability in the legal system.⁵⁸ By contrast, the institutional role of international adjudicators is more constrained. When determining the content of a CIL norm, adjudicators can proceed acceptably only by attempting to reconstruct the intentions of those states that have engaged in relevant practice and substantive argumentation in relation to a putative CIL norm.⁵⁹

In the second place, framing helps to impose order and priority in the virtual infiniteness of state practice. One cannot hope to isolate those elements of state practice that would be relevant for examination, or to assess their legal relevance, unless one has already framed with some degree of specificity a legal problem to resolve or a legal goal to achieve. If, for instance, one wishes to advocate for a new, less strict content of the CIL minimum standard of treatment of aliens in the context of foreign investment protection, one should look for evidence of such content, among others, in the development of investment treaty provisions over time, interventions made by states before international forums such as UNCITRAL or UNCTAD, positions taken by states in arbitration or in non-disputing state party submissions made in the context of investment disputes, relevant diplomatic exchanges, or even judgments by domestic courts addressing grievances of foreign investors.⁶⁰

At the same time, the weight, authority, or priority of different sources of evidence of practice are all relative, meaning that some materials of practice may only be relevant prima facie and that an assessment must be made case by case.⁶¹ Thus, in the third place, framing the legal issue appropriately also helps the interpreter to determine the kind of practice they should establish or look for.⁶² For example, in Nicaragua v. Honduras, the ICJ considered in obiter that in certain circumstances the application of the CIL principle of uti possidetis could be extended to the delimitation of maritime boundaries (as opposed to being confined to the determination of territorial boundaries), in particular when this is in connection with historic bays and territorial seas.⁶³ No new evidence of state practice or opinio juris was offered for this statement, yet arguably none was needed given the framing of the issue. That is, extending the application of uti possidetis from the determination of territorial boundaries to the delimitation of some maritime boundaries may be said to have been a continuation, by analogy, of the ICJ’s prior conclusion, in Frontier Dispute, that uti possidetis is a ‘principle of a general kind which is logically connected with … decolonization wherever it occurs’.⁶⁴ Put differently, from the point of view of the juridical aim of securing respect for existing boundaries at the moment of independence,⁶⁵ determining a maritime boundary between two newly independent states following decolonisation is not unlike determining a territorial boundary between them.⁶⁶

In short, framing kick-starts the interpretative enterprise by singling out what is, prima facie, legally relevant in determining the content of a CIL norm. In doing so, one necessarily ‘bakes in’ certain assumptions, notably about the existing state of the law, about acceptable ends to be pursued, and about one’s institutional role and capacities in the international legal system.⁶⁷ Framing thus goes hand in hand with an often-implied process of normative contextualisation.

4.2 Contextualising

Implied in framing is contextualising. The latter involves seeing one’s object of enquiry against an accepted system of background knowledge so as to infer normative content out of it. In the case of CIL, contextualisation takes place when seeking to determine the existence of a CIL norm by carving out an area of relevant practice, and also when seeking to determine the meaning or scope of an already established CIL norm by re-assessing practice that has already been identified in the past. In that sense, like framing, contextualisation in CIL interpretation is indispensable, since mere regularity of conduct cannot lead to a normative conclusion on its own and in the absence of some background context.⁶⁸ That is, a collection or a pattern of state conduct cannot by itself be transformed into a reason to act in any particular way absent a rule, goal, or principle acting as the normative context that creates the necessary connections between the observable instances of conduct.⁶⁹

Contextualising practice is an interpretative act, in that it can in principle take place at various levels of abstraction. A pattern of conduct may be identified as relevant state practice when seen against broad areas of international law that already include a network of rules, goals, or principles (e.g. use of force, treatment of aliens abroad) as well as against specific international legal rules or doctrines (e.g. uti possidetis, minimum standard of treatment of aliens). Fixing the level of abstraction thus becomes a choice of critical normative importance. The chosen level of abstraction determines not only whether one has identified enough evidence of practice to formulate a CIL norm, but also whether the identified evidence is of the right sort or whether altogether different evidence must be looked for instead.

Take the ICC appeals chamber decision in Al Bashir, which held that there was no CIL rule of head-of-state immunity before international courts (as opposed to before domestic courts) that is applicable in the horizontal relationship between states in situations where the ICC has issued an arrest warrant against a head of state.⁷⁰ Put differently, for the appeals chamber, head-of-state immunity would not apply even if the ICC had requested the surrender of a head of state who hailed from a non-state party to the ICC. The ICC appeals chamber concluded so after pointing to the fact that no evidence of practice or opinio juris could be adduced for the existence of a CIL rule of head-of-state immunity in these situations.

For present purposes, one can point out the following vis-à-vis the content-determinative nature of contextualisation. The ICC seems to have initially framed the pertinent legal question adequately (i.e. does head-of-state immunity apply between state parties and non-state parties to an international court when that court has issued an arrest warrant against a head of state?), yet seems to have contextualised its assessment of observable practice narrowly compared to the question (i.e. is there evidence to suggest a rule that states recognise immunity for each other’s heads of state when an international court has issued an arrest warrant?).⁷¹ Having done so and having observed no such evidence, the ICC appeals chamber came to the inescapable conclusion that no rule of CIL exists mandating immunity in these situations.

The outcome could have been markedly different had the contextualisation taken place at a higher level of abstraction, for instance by considering the underpinnings of the doctrine of head-of-state immunity. If one takes the view that the doctrine derives from the principle of sovereign equality, then the fact that the immunity may be raised before an international rather than a domestic court becomes immaterial. Instead, what would be critical is whether the head of state whose immunity is waived is a national of a state party to the international court in question. If they are not, the CIL rule on immunity would still apply, since waiving it would violate the principle of sovereign equality.⁷² Moreover, making the latter argument does not require one to search for additional evidence of state practice or opinio juris. In fact, it makes the kind of evidence that the appeals chamber was searching for in this instance beside the point.

Crucially, despite the critical interpretative importance of contextualisation, there appear to exist no determining criteria, and no defined metarules, for what the appropriate level of abstraction is in each case a CIL interpreter contextualises practice.⁷³ The case rather seems to be that the CIL interpreter, much like other practitioners grappling with doubt or ambiguity in law and elsewhere, must make such determinations on the spot, in the act of interpreting, and without the benefit of hindsight.⁷⁴ In the absence of guiding metarules, a conscious and active process of reflection may thus be the only kind of safeguard an interpreter of CIL has.

4.3 Reflexivity

Thinking reflectively consists in ‘turning a subject over in the mind and giving it serious and consecutive consideration’, says John Dewey.⁷⁵ According to Dewey, reflective thinking can be a useful method to safeguard one’s inferences from falling into obvious errors.⁷⁶ Perhaps the best-known contemporary exposition of reflective thinking comes from John Rawls and his concept of reflective equilibrium as a technique of justification.

Roughly put, the idea behind reflective equilibrium is that we must work back and forth in our reasoning between various levels of abstraction, including between our judgements about particular instances or cases, the principles that we believe underpin those judgements, and the theoretical considerations that we believe bear on accepting our judgements and principles, while revising any of these elements whenever necessary in order to achieve an acceptable level of convergence among them.⁷⁷ An acceptable level of convergence, according to Rawls, is ‘wide’ rather than ‘narrow’. That is to say, we should not seek only mere consistency among our judgements, but we should also strive to ensure that some of these judgements provide the best justification for the others. Therefore, it is acceptable for prior judgements to be modified or new judgements to be added during this iterative process.⁷⁸ The goal is to achieve an ‘optimal’ equilibrium before stopping the enquiry. We arrive at an optimal equilibrium when the component judgements, principles, and theories of our reasoning are such that we are not inclined to revise any further, because, taken together, they have the highest degree of acceptability or credibility.⁷⁹

The reflective equilibrium technique has strong similarities with the understanding of coherence put forward in this chapter as interdependence, mutual supportiveness, and a web of propositions exhibiting axiological compatibility. Not only is interdependence of judgements a core feature of reflective equilibrium, but also the latter’s iterative process precisely seeks to ensure that one’s judgements converge by being mutually supportive and able to stand together as a unit, as the concept of coherence indicates. In short, reflexivity and coherence are conceptually linked. Exhibiting reflexivity in one’s practice is conducive to coherent reasoning, which, in turn, is conducive to a well-justified outcome, substantively as well as methodologically.

A reflexive attitude must thus permeate the entire process of CIL interpretation, permitting and indeed instructing interpreters to critically evaluate and, if need be, amend their interpretative choices and moves before fixing the exact scope of a concrete CIL rule to be applied in the case at hand.⁸⁰ No aspect of the process is beyond the possibility of re-assessment and amendment, including, critically, the framing of the legal issue/goal, the chosen level of contextualisation, and the concomitant normative weight assigned to every observable piece of evidence of practice. This makes CIL judgements essentially axiological overall.⁸¹ Every interpretative step taken in ascertaining the content of CIL is to be assessed for its conformity to the identified normative background, its consistency with the implications created by earlier argumentative steps, and its practical consequences (whether desirable or problematic) – all combining to yield an appropriate resting place for the interpretative enquiry.⁸²

I must make a caveat here. It is not at this point possible to offer a practical example of reflective thinking in CIL interpretation. Much like argumentation in general, putting forward legal arguments or handing down judicial decisions on the content of CIL are performative acts to some extent. That is to say, when expressed publicly, legal argumentation and judicial decision-making are constructed so as to persuade an audience that the argument or decision in question contains well-chosen premises and that the outcome follows rationally from these premises.⁸³ There is an inherent difficulty in examining reflective thinking taking place live in practice from that point of view, since any prior act of active reflection during the argument-forming or decision-making process would presently be obscured to the audience.⁸⁴ The audience may then only make reasonable retrospective inferences about the reflective thinking likely at play behind the finalised version of the argument or decision presented to them.

Nevertheless, this does not take away from the importance of reflexivity as good practice of an interpreter’s moral responsibility, particularly in light of international law’s arguable character and legal reasoning’s practical nature.

5 Conclusion

This chapter has argued that it is both necessary and possible to strive towards coherence in the interpretation of CIL, once coherence is properly understood as an independent concept having both a substantive and a methodological dimension. This dual dimension of coherence is critical to law and legal reasoning. It means that coherence in law is more than a mere goal or a vague, results-oriented ideal. It is also a method of constructing one’s reasoning and of deliberating about one’s interpretative choices. The dual dimension is especially important when reasoning in practical settings (and legal reasoning is one such example), where one commits to action and where interpretability of ends is a core aspect of the process. The chapter has concluded by arguing that striving for coherence in the interpretation of CIL means being cognisant of three kinds of processes – namely, framing, contextualising, and iteration/reflexivity. These can serve as indicators of the coherence or incoherence of proposed CIL interpretations. However, the three processes are themselves interpretative in nature and therefore may be the subject of debate and reasonable disagreement.

To be sure, thinking about coherence, legal reasoning, and interpretation in the manner argued here raises fundamental questions about the nature of international law and the prevailing doctrine of sources. These are important and heavily implicated issues in the present analysis, which, however, I have not begun to address in this chapter. What can be said for the moment is that, if persuasive, the present analysis gives us at least an impetus to re-examine key tenets of legal positivism in international law and to re-assess the degree to which they comport with how international actors seem to reason and argue about international law in practice.