Not all ontological concerns which surround the concept of (customary) international law (CIL) have disappeared, rather they have shifted. Whereas the existence of a genuine international legal system is taken as a ‘given’, questions still remain about its genesis and the position of CIL within it. Some, for example, still question whether we can truly speak of customary international law, while others recast the concept of CIL through a formalist perspective. Accordingly, formalism, in its moderate form, treats formal sources, documents and/or proclamations as ‘better’ tools for both (a) the preservation of existing rules of CIL and (b) the ‘creation’ of new legal rules. At its more extreme, formalism purports the view that (c) IL (or even CIL) finds its genesis only in formal sources, documents or proclamations. While some formalisation is undeniably helpful and even necessary, we should be more critical of this formalist paradigm. In this way, the chapter seeks to respond to these positions through a revival of the legacy of Sir Henry Maine and the evolutionary conception of law for which he laid out the first foundation. By operationalising this conceptualisation, a new vision spawns for CIL: a vision beyond mere formalism.

Customary international law is one of the formal sources of international law and plays a pivotal role in the existence and functioning of the international legal system. Although for a rule of CIL to emerge a widespread, representative, constant and virtually uniform state practice is required, accompanied by the requisite opinio juris, that does not necessarily mean that CIL is a slow and archaic process, which has been overcome by extensive treaty-making. On the contrary, CIL remains a vital element in the corpus of international law that is open to refinement, clarification, development and evolution. This process does not happen only through the classical emergence and/or subsequent modification of the rule, but also and perhaps most importantly through the process of interpretation. This chapter demonstrates this by showing that CIL interpretation is neither problematic from a theoretical perspective, nor is it the only example of interpretation of unwritten rules. This is further reinforced by jurisprudence taken from both the domestic and the international legal system, although such interpretative exercises are not without their limits. What emerges from this analysis is that CIL interpretation, as Sur has beautifully noted, is of a negentropic nature that constantly nourishes and updates CIL.

This chapter on the Re-constructing the construction of Laval: Studying EU law as a social interpretive process focuses on one of the most controversial ECJ rulings in recent decades. Trying to understand how this particular ruling became so controversial, this chapter presents an analytical approach that views the construction of EU law as an interpretive process, which concerns not only the meaning of a specific ruling, but also its importance in terms of setting crucial precedence and in terms of having impact on European society. The chapter argues that to understand how Laval became so important, we must study the case as a protracted process of social, legal and political construction, in which a diverse set of actors – such as lawyers, legal scholars, politicians and trade unionist – all contributed to enchanting the case’s significance both before and after the ruling itself. Tracing this interpretive process, the chapter shows how the political context (of EU enlargement and Services Directive) and the legal context (of other somewhat related rulings) were knitted together to make Laval a symbolic stake in a struggle regarding the future of the European Union. Doing so, the chapter illustrates how a methodological approach which centers less on the ruling itself, but more on its social and political construction, can shed new light on how EU law is created. At the same time, the chapter takes the study of the Laval case as an opportunity to discuss the underlying principles of this processual approach, the challenges of its practical implementation and its limitations.

This chapter serves as a critical appraisal of whether the practice of non-state armed groups (NSAGs) shall be incorporated into the formation of customary international humanitarian law (IHL). It argues that customary IHL is not bound to suffer from the legitimacy flaw even if its formation does not incorporate the practice of NSAGs, and that admitting NSAGs into the formative process of customary IHL does not necessarily bring out better compliance records. Nevertheless, if it may be admitted that such a move is still theoretically possible and, in some ways, desirable, an NSAG should be considered a qualified creator of customary IHL so long as it can engage in an armed conflict, and its positive and negative practice should both be taken into account. Incorporating the practice of NSAGs would have legal implications for not only the theory of customary international law but also the contents of IHL. It may challenge the unitary character of customary international law, the equal application of IHL and the existing protective standards of IHL. At present, it is not unreasonable to stay sceptical about whether incorporating the practice of NSAGs marks a correct direction for the future development of IHL.

The chapter argues that fieldwork – specifically multi-sited, semi-structured interviews and participant observation – is uniquely suited for unpacking how the constraints of daily practice within national courts frustrate the subnational reach of the European Union's (EU) legal authority. Deriving methodological insights and practical lessons from fifteen months of fieldwork in Italian, French, and German courts, the author shows how fieldwork reveals judges to be neither solely driven by individual attitudes nor by strategic quests for power: they are also employees within a bureaucracy. Anchored by the demands of established practice, knowledge, and everyday work, judges can develop an institutionally rooted consciousness resisting disruptive confrontations with new and unfamiliar rules like EU law. Through on-site iteration and triangulation, field researchers can trace, unpack, and corroborate this consciousness in real time, with an eye to also hypothesizing the conditions under which resistances to Europeanizing change can be overcome. In so doing, the researcher can intercept what one judge referred to as a ‘bureaucratic silence’ within which EU law ‘dies’: A web of habitual institutional practices scarcely detectable via other modes of social inquiry.

The man who sacrifices the possible in search of the impossible is a fool.1

There is a profound ambiguity surrounding all elements of CIL, particularly as regards the psychological element of opinio juris. This is further accentuated by the prevailing, in international law, elements of absence, silence or non-action and their often-monolithic interpretation as non-objection or, even, acquiescence. But is this true, according to the rules of informal logic? What is the value of non-doing? Non-acting or abstaining? Non-believing towards the formation of a certain opinio juris? The mainstream interpretation of CIL overlooks the quantifications and varieties of meaning in non-appearances, such as the conceivable neutrality of absence. This has led to persuasive-teleological argumentation, in the sense that the person or agency elaborating on either absence or silence aims at a certain end and is thus characterised by a certain ‘argumentative orientation’ towards a preferred conclusion. In this spirit, the ICJ has developed several techniques of superficial, persuasive argumentation, teleologically governed by the non liquet principle, the containment of international crises and the effective resolution of international disputes. This repositions the whole enquiry to the proper place of informal logic in international legal reasoning. The author suggests that an open-system approach could shed light on these inconsistencies and political manoeuvres.

This chapter addresses the question of how the CJEU engages with its own past cases in its reasoning. The chapter focuses on how to identify the most legally authoritative precedents in the CJEU non-discrimination jurisprudence that implies a corpus of cases. Frese shows empirically how the corpus of CJEU cases, built over the course of the past sixty years, assigns different degrees of authority to each case according to how the court uses them. This chapter demonstrates that the network approach to the study on precedent provides a highly useful method, which has the specific advantage of shifting the viewpoint of which cases are authoritative from the scholarly perspective to the CJEU’s perspective by tracing the court’s own references and citations to its past cases. In departing from traditional theories of what precedent is and how it constrains, the chapter operationalizes the concept of precedent as, initially, a mathematical authority. By mapping all the references and citations between cases, it is furthermore shown how the court itself creates legal ‘authorities’ in its jurisprudence as it cites some cases very frequently while others less. By highlighting how the network approach provides useful tools for understanding the CJEU’s reasoning and decision-making practices, the chapter also shows that this approach should refine and supplement, rather than substitute, EU law doctrinal analyses.

One characteristic interpretive technique in the discourse of customary international law is the identification of such norms as 'possibly emerging' or possibly in existence. Thus it is frequently asserted that a putative norm 'may' have or 'probably has' customary status. This hypothetical mode of analysis can give rise to the speculative construction of international obligations driven more by preference than by evidence. This speculative rhetorical technique is examined by reference to the account of temporal dimensions of the emergence of customary international law provided in the Chagos Archipelago Advisory Opinion of 2019. Here the International Court of Justice endeavoured to pin down the time of origin and path of evolution of a customary norm requiring territorial integrity in the context of decolonialisation as self-determination. This chapter engages with this ubiquitous characteristic of the interpretation of customary international law and argues that the accompanying opacity in relation to international legal norms – norms that are held to generate obligations – is to be deplored.

The methodology for identifying customary international law has long been established, most prominently in the jurisprudence of the International Court of Justice. This methodology has also recently been affirmed by the International Law Commission. International courts and tribunals have nevertheless adopted various shortcuts in their legal reasoning when ascertaining the existence and content of customary international law. The use of such shortcuts does not always withstand scrutiny, particularly where evidence of State practice and opinio juris is divided or scant. This is also the case where conclusions are drawn exclusively on the basis of certain written materials, prior decisions of other courts and tribunals, or the work of the International Law Commission which, more often than not, combines elements of codification and progressive development. While recognizing that international courts and tribunals face institutional and practical constraints, this chapter argues that they should nonetheless show greater care in their legal reasoning and demonstration of customary international law, absent which they risk being perceived not only as the idle scribes of custom but as law-making agents proper, which may in a long run damage both the authority of their decisions and that of custom itself as a source of international law

The ‘cliché’ two-element theory of customary international law can provide a simple solution against the legion of alternative theories. As a manifestation of international law that does not directly spring from the ‘will’ or ‘consent’ of states, it reflects their perpetual international relations. States do not voluntarily form a will at the international level but consciously or unconsciously influence its creation through their actions. Following the metaphor of ‘Schrödinger’s custom’, until an observer is introduced to determine what the particular customary rule is in a certain moment, customary international law remains ‘mixed or smeared’. This chapter builds on the instructive value of realism when dealing with states, focusing on the interplay of their interests in the formation of customary international law. While it is obvious that parties bring such interests to the table when negotiating a treaty, it appears less obvious whenever scholars seek to harness custom for the normative project of international law. The chapter argues that more even than other sources, customary international law will most likely reflect an equilibrium of interests. Thereby, effectivity and reciprocity, as the catalysts of international law formation, guide the identification of the legal status quo.

This chapter proposes an inquiry into the surface of EU law. This implies a non-formalist study of legal forms such as legal sentences, concepts and techniques, a rich field of inquiry in itself. These are not mere tools, totally under control, used to achieve certain ends defined in other terms, outside the law. They are far more intriguing and fascinating than that. These legal forms participate to the constitution of legal and social realities that they pretend to regulate. They enable and limit what participants of a language-game can do, and they can even influence what they may want to do. The proposed methodology to study the CJEU implies focusing on law and legal concepts as a set of knowledge practices and inquiries on the transformative power of legal techniques. It should be distinguished from classical studies on the court, mainly dealing with interpretation, as well as from works focusing on power relations between legal actors. Through the presentation of some cases in EU citizenship case law, this chapter focuses on the constitutive dimension of the legal controversy surrounding the Court of Justice of the European Union’s rulings.

With the inescapable constructive dimension of CIL, courts serve a key function in the development of CIL through their interpretations and their interpretative methodologies. Sometimes courts are mistaken in their interpretation of CIL. This contribution explores three main questions: (1) what is misinterpretation? (2) how and why do misinterpretations take place? and (3) what are the potential consequences of misinterpretation of CIL? These all converge in the underlying question of whether there are detectable objective standards for the determination of misinterpretation or whether such observation is always a subjective one – anchored on a disagreement on the values which lie at the core of international law. To preserve legal certainty and predictability in the interpretation of CIL, it is crucial to recognise that courts are not infallible, may lack the requisite methodological tools and occasionally just get CIL wrong. The indeterminacy of CIL renders futile the attempts to pin down precise conditions for its validity, and simultaneously, leaves open the definition of misinterpretation of CIL.

This final chapter uses the shift metaphor to suggest that change might be limited if not explicitly anti-racist. In the absence of this consciousness, a shift can be sidewards rather than forwards. I argue that empirical studies in EU law can only take a shift forwards when the principle and practice of decolonialism is embedded in it. This requires recognition of Europe's colonial past as well as racism in the present. The assumption that all Europeans are White, and all Blacks are migrants has to be debunked – Black European scholars need to be encouraged to take their place in the field and given access to resources to ensure that empirical research in EU law also focuses on experiences important to their lives.