When we interpret customary international law (CIL), what is it that we actually interpret? The most promising option is that interpretation of CIL is an interpretation of legal practices. However, the dominant two-element doctrine of CIL assumes that opinio juris generates both legality and normativity of practices, when the latter have no independent normative significance. The chapter challenges this view by drawing on jurisprudential ideas that define practices as inherently normative. This view allows to differentiate between two instances of interpretation of CIL. One is focused on clarification of the normative content of state practices, another is focusing on identification of these practices as legal ones. Interpretation as clarification involves assessing structures of practical reasoning. Interpretation of CIL implies establishing connections between first- and second-order reasons that form the practice and give it meaning. This entails that interpretation of CIL focuses on dynamics of reasons, their inclusion and exclusion within an existing normative framework. Interpretation as identification involves showing that existing second-order reasons meet a threshold of legal validity, which may take the shape of opinio juris, but may as well be functional, when legality of a practice is linked to its relevance in a broader set of legal practices

In his chapter Nicholas Haagensen seeks to articulate the processes of legal construction and elaboration in a novel area of EU financial and monetary law. Using qualitative methods, he explains how EU lawyers, first, built a novel legal structure – the European Stability Mechanism (ESM) – during the Eurozone crisis in the years 2010 to 2012, and second, how they defended their construction before the CJEU. While attempting to resolve the legal tensions arising between the EU legal order and the ESM legal framework, the CJEU backed the mutation of Europe’s Economic and Monetary Union (EMU) with its ruling in the Pringle judgement. The establishment of the ESM – an international financial institution – outside EMU, while still being intimately connected to the EU legal order, instigated a mutation of EMU through the introduction of international law modalities into its EU law foundations. Drawing on interviews with lawyers from the European Commission, the Council, the European Parliament and the ECB, as well as the legal observations of all the parties to the Pringle case, the chapter explains and maps the process of legal construction and elaboration of changes to the EMU legal structure.

Strategy is harder than tactics because you have more time to act and thus more time to doubt. Also, in tactics you can see what is going on, in strategy you have to guess.1

Sovereign States are under a legal obligation to comply with customary international law even though they have not explicitly consented to these norms. How should international courts accommodate both such non-consent-based CIL and a commitment to state sovereignty? The article outlines one strategy that avoids or helps address challenges wrought against other attempts to create more consistency and coherence between CIL and the other sources of international law – whilst securing a central role for state consent. A plausible account of why states have an obligation to honour treaties they consent to also contributes to justify their obligation to honour CIL norms. The shared normative basis for both sorts of obligations may be a ‘Principle of Non-manipulation’, a norm to not violate intentionally created rightful expectations. The account draws much on Scanlon, MacCormick and Hart.

This chapter deals with a topic not very often discussed in the study of customary international law (CIL): the use of customary international norms in the internal legal order of a state. The use of these norms (regulating the relationship between states) is particularly relevant for federal states. The chapter studies the use of CIL norms in two federal states: Germany and Austria. In Germany, CIL norms became part of the domestic legal order through the 1919 Constitution. German courts used those norms to settle disputes between German states in those cases where the federal framework did not offer clear solutions. Under the 1949 Basic Law, the Federal Constitutional Court has been inconsistent on the question whether the constitution allows for the use of customary international norms to settle disputes among German states, but at the very least it uses norms that are materially identical to customary norms in international law. In Austria, the federal constitution expressis verbis acknowledges the use of international norms in the domestic legal order to regulate interstate relations. It is not entirely clear however whether these norms are of a customary nature, or are simply those found in the Vienna Convention.

The chapter focuses on the judicial mobilisation of the trade unions before the European Court of Justice in the well-known Viking and Laval cases. It asks how to use the personal archives of the EU lawyers to better understand litigation strategies, by analysing the digital archives (emails and attachments) of a trade union lawyer from the European Trade Union Confederation (ETUC) involved in the mobilisation. Firstly, the chapter discusses the analytical benefits and methodological problems raised by this rare kind of empirical material that brings new qualitative insights on the practices of the litigants behind the official scene. Especially, this material asks ethical and legal questions around confidentiality and privacy that should be addressed. Secondly, thanks to these digital archives, the author brought a new understanding of the issues at stake in the Viking and Laval cases, by focusing on two examples: the judicial lobbying of the Swedish trade unions in the Laval case, and the role of the trade union legal experts in framing the legal and political issues of the two affairs.

The scholarship on sources of international law has not satisfactorily answered these questions: are sources regulated by any ‘rules’? Are ‘rules on sources’ part of international law? What is the source of ‘rules on sources’? The standard answer to these questions is that sources are regulated by state practice reflected in Article 38(1) of the Statute of the International Court of Justice. This position, albeit professing to be practice-based, does not account for the existence of ‘rules on sources’, nor for their legality and source-based character. Other practice-based positions have also proven insufficient: some, postulating the legality of rules on sources, fail to address their source-based nature; others, affirming both the legality and source-based character of rules on sources, and invoking custom as source thereof, fail to substantiate their claims, which are merely asserted or based on decisions of early arbitral tribunals, thus assuming custom to be judge-made (a ‘custom in foro’). This chapter examines the suitability of custom as source of rules on sources and proposes a shift away from custom in foro towards customary international law proper, established by state practice invoking ICJ Statute Article 38(1) outside ICJ proceedings, major instances of which it surveys.

Newspapers as the main media of political coverage continue to be primary outlets for reports and opinions on collectively binding decisions. Following a quantitative research strategy, this chapter introduces a new methodological approach that allows us to systematically capture media attention and public salience of court decisions. It provides insight into a new dataset for newspaper coverage of more than 4,000 CJEU decisions in eight EU quality newspapers. The chapter describes the data collection process, the structure of the data, and the opportunities for quantitative analysis. Moreover, it emphasizes the general applicability of this methodological approach for a large number of court cases across a longer time period. The collected data offers new insights into media attention to CJEU cases and various opportunities for future analysis. The contribution also reflects on limitations, strengths, and weaknesses of this quantitative approach of studying the CJEU, compared to other approaches presented in the volume.

Since 2008 the Universal Periodic Review (UPR) mechanism of the UN Human Rights Council has become a fixture of the international human rights regime, reviewing the human rights record of every single state once every few years. Over the course of the UPR reviews to date thousands of recommendations have been issued about the protection of human rights with a growing body of evidence showing that states modify their behaviour in response to the outcome of reviews. This chapter analyses how UPR recommendations can be used to identify customary international law. Using the discussion on the identification of custom in General Assembly resolutions as a starting point the chapter examines how scholarship on the identification of custom has argued that there are a different set of rules for the identification of customary international human rights law. Identifying custom in UPR recommendations can help resolve some of the ambiguities and contradictions in relation to the identification of customary international human rights law. This chapter concludes by outlining a three-part model for identifying custom in UPR recommendations which would complement existing rules for identifying customary international law.

There is a fundamental, eternal and unresolvable conundrum at the heart of customary international law (CIL): we do not know on what we should base our arguments. The debates on the theory of CIL continue unabated, because there is a strong belief that we need it in order to keep international law working. But is that legal reason enough to consciously or subconsciously change the mechanics of customary law to suit these needs? The ILC’s CIL project is suffused with the spirit of pragmatism, but it could not avoid taking a stance on theory. On the other side are foundational critiques of CIL, like Jean d’Aspremont’s: custom is merely a story international lawyers tell themselves. Both methods have virtues and very dangerous vices and contain the seeds for their own destruction. One aim of this chapter will therefore be an effort to show the relative merits of these techniques from a theoretical point of view. My portrayal usually stops at the recognition that we cannot find the law which tells us the rules of CIL-making. In this chapter, I will attempt to go a step further to a new method for conceptualising this: the Approximatively Plausible Empowerment Norm.