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24 – 25 May 2019 / University of Groningen


1. What are the rules, if it is rules we are talking about, that regulate the (functioning of) sources of international law – in particular of customary international law?

This question invites an analysis of the rules that regulate the sources of international law, with a specific focus on customary international law (CIL). In this sense, the question aims at an analysis of the meta-rules governing the sources of international law, in order to sketch the rules governing the identification of CIL and, therefore, contribute towards a discussion on the formation of rules for its interpretation.

2. Is the classical paradigm of state practice and opinio juris still valid today?

Scholars have identified several problems in the current paradigm, which put into question whether the ‘state practice and opinio juris’ formula is still valid today. In light of this, this question invites a discussion revisiting the classical paradigm of CIL, exploring the origins of this paradigm and testing whether it adequately reflects the manner in which customary law emerges and is identified today. Research may also question whether and to what extent the dominant practice is relevant on the level of the meta-rules.

3. Are there alternative approaches that can offer a better model describing the emergence and functioning of rules of customary international law?

This question intends to explore whether alternative theories of international law might offer a model that more aptly describes the emergence and functioning of customary rules, including whether aptitude in this sense is or should be a relevant test. Within its scope, speakers may pursue various research avenues, including: an exploration of non-traditional approaches which challenge the classical paradigm of state practice and opinio juris, an evaluation of the question whether States are the only actors whose practice is conducive to CIL rules, an examination of alternative legal theories, to name a few.

4. Can customary international law be interpreted? Are rules of customary international law open to interpretation in the same way as those of treaty law?

The interpretability of treaty rules is unanimously accepted and, moreover, is a topic discussed extensively in legal literature. This is not the case, however, when it comes to the openness of CIL to interpretation, which is both an under-researched topic and a matter on which the opinions of scholars are divided. Some scholars accept the possibility that CIL may be open to interpretation, in spite of it being an unwritten source of law, whereas other scholars strongly oppose it. The answer to this question, then, seeks to explore the issue of interpretability of custom and the convergence and/or divergence between the interpretability of custom and the interpretability of treaty rules.

5. Do domestic approaches to customary law (either domestic or international) differ from those in international legal scholarship? What lessons can be learned (or tools adopted) from domestic approaches to customary law?

This question explores the points of similarity and difference between domestic and international approaches to the interpretation of customary law. Within this question, you may look at the interpretation of both domestic and international customary rules, whether by domestic practice (including) courts or in domestic doctrinal traditions. This may involve, for example, a comparative study of the approaches of domestic and international courts, in order to identify points of convergence or divergence between the theory and practice on both levels.

This question also explores the lessons that can be learned from domestic practices of interpretation of customary law. Within its scope it may be relevant to look into the methods of interpretation employed by domestic judges when engaging with customary law (both domestic and international), in order to see whether judges engage in induction, assertion, deduction, or possibly another method, and whether this choice of methodology depends on the domestic legal system. The aim of the question is to examine domestic approaches across a variety of national systems, in order to explore whether they can inform international practice. Moreover, if the research points to similarities between the domestic approaches of multiple states, this question seeks to explore whether these approaches may be generalized and extrapolated on the international level.

6. Is hermeneutics relevant to customary international law?

This question addresses the relevance that theories of hermeneutics (in a wide sense) may have in the case of CIL. Hermeneutics, defined as the science or the methodology of interpretation seeks to understand the ways in which humans deduce the meaning of texts, verbal communication, actions and so on. Hermeneutics also discusses what material can be classified as meaningful and can, thus, be qualified as a valid object for interpretation – a question of special importance for determining the interpretability of CIL. Additionally, it assesses the different variables such as intention or context, that serve an important role in the interpretative act. Therefore, this question aims at exploring, first, the importance of this branch of philosophy for CIL and, second, how hermeneutics is relevant for the subject of the interpretation of custom.

7. Is there a difference between the interpretation of state practice compared to the interpretation of a rule of customary international law?

Oftentimes courts and authors employ the terms ‘interpretation of state practice’. In light of this tendency, this question proposes an examination of whether the interpretation of state practice for the purposes of identification of a CIL rule in the classical paradigm of state practice and opinio juris) is identical to the interpretation of an existing rule of CIL or whether there are differences between the two and, should the answer be in the affirmative, what these differences are.

8. Where do lines between identification, interpretation, application and modification of a rule of customary international law lie?

Considering that CIL rules lack the precision of treaty rules, in the case of the former the lines between identification, interpretation, application and modification are often blurred. This is especially visible in international judicial practice, where judges resort to different operations to decipher the meaning or the scope of a customary rule. The aim of this question is therefore to identify how these operations can be differentiated, in order to determine the moment when rules of the interpretation of CIL will come into play.