Table of Contents

Research Handbook on the Law of Treaties

Research Handbook on the Law of Treaties

Research Handbooks in International Law series

Edited by Christian J. Tams, Antonios Tzanakopoulos and Andreas Zimmermann

Offering a unique conceptual approach to the Law of Treaties this insightful Research Handbook not only sets out the foundational issues, but identifies tensions within the field, including formalism vs flexibility, integrity vs flexibility, and uniformity vs specialisation, to name a few. It seeks to define and re-define the dimensions in which Treaty law operates, tracing its fault-lines and the challenges it faces, such as breaches, regime-collisions, state succession and armed conflict. Representing a broad range of jurisdictional and ideological perspectives, the Research Handbook provides a diverse and stimulating approach to international treaties.

Chapter 9: Formalism versus flexibility in the law of treaties

Jean d’Aspremont

Subjects: law - academic, public international law, politics and public policy, international politics, international relations


The common narrative about treaties is rather one-dimensional. Both treaties and their legal regime are meant to be formal. First, treaties themselves, albeit possibly made through non-formal processes, are usually construed as formal instruments aimed at regulating a given aspect of international life. Second, and more fundamentally, the making, identification, validation, application, interpretation, modification and termination of treaties are regulated by a set of formal constraints meant to formally organize various aspects of their existence and functioning. In that sense, treaty law is traditionally perceived as a toolbox providing instruments for the formal translation of the exercise of public authority at the international level. Treaty law thus contrasts with customary law, which in some ways could be seen as the realm of laissez-faire. This contribution aims to show that the law of treaties can be read very differently, and that the dominance of formalism in treaty law is much more nuanced and qualified than the general perception sketched out in the preceding paragraph suggests. It will be argued that from its making to its termination, a treaty see-saws between formalism and flexibility, and that the body of rules designed by international lawyers to regulate the life of treaties mirrors this constant oscillation: the law of treaties, as codified in the two Vienna Conventions (the 1969 Vienna Convention on the Law of Treaties and the 1986 Vienna Convention on the Law of Treaties between States and International Organizations or between International Organizations), displays both formal rationality and flexibility.

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