Sources of International Law in Domestic Law: Relationship between International and Municipal Law Sources

Abstract

This chapter maintains that as both municipal and international law use legal norms to regulate social relationships, a space for inter-systemic interaction between both legal spheres emerges. Municipal legal practice can have an ‘upstream’ impact on the formation of the content of the sources of international law, where these require proof of State practice and/or opinio juris for valid norms to be generated. Particularly, domestic court decisions can have a jurisgenerative effect on customary international law, where they become part of a transnational dialogue between domestic and international courts on questions of international law determination. Admittedly, this dialogical process is hamstrung by the particularities of domestic law and the hard-to-eradicate selection bias of international law-appliers. However, a more objective comparative international law process can be grounded, geared to effective problem-solving guided by the persuasiveness and quality of reasoning of municipal court decisions relevant to international law.