Treaty and Custom in International Law

Extract

[...] A cooperation in the service of normative production The treaty as a vector of expression of customary law Treaties serve as a factor of diffusion of customary law: states that become parties to a treaty often consolidate in their practices, the customary principles that it consecrates. Ex: the rule pacta sunt servanda is conventional and customary. Treaties are a tool for crystallizing custom: ICJ, North Sea Continental Shelf, 1969. Vienna Convention (1969): reaffirmation of important customary principles Custom completes conventional regimes The judge has recourse to custom to frame or correct treaties. Custom applies in the absence of an existing treaty: ICJ, Nicaragua, 1986. [...]

[...] + The specifics of imperative norms (jus cogens) and their impact on interactions. The tensions arising from the articulation between treaty and custom International law is fragmented, it promotes competition between treaty and custom: multiplication of specialized regimes (WTO, ECHR, ad hoc penal tribunals). The judge must sometimes arbitrate tensions between sources: Case Gabcíkovo-Nagymaros, 1997 + Many political implications: inequalities in the production of law: The great powers influence customary practices and southern states sometimes use conventions as a means to counter customary practices. [...]

[...] This permanent dialogue feeds both the idea of a coherent international order but also of a system in tension. The treaty is the formal mode of production of international law, it is the immediate expression of the consent of states and is framed by the Vienna Convention of 1969. Custom, on the other hand, is based on the combination of a sufficiently general practice and an 'opinio juris', as recalled by article 38 of the ICJ statute which mentions 'international custom as evidence of a general practice accepted as law'. [...]

[...] From this gap, a rather complex relationship is born: complementarity refers to the idea that treaties and custom enrich each other, particularly when conventions codify or 'crystallize' a pre-existing right. On the other hand, competition refers to situations where the two sources seem to dispute the normative terrain: contestation of codified rules, appearance of practices contrary to conventional provisions or even customary evolution despite an in-force treaty. The interest of the subject is first theoretical: the coexistence of these two sources questions the very foundations of international law, shared between the logic of state consent and the emergence of norms based on objective requirements of the international system. [...]