Speakers: Prof Mads Andenas & Prof Johann Ruben Leiss, University of Oslo

Lecture summary: The lecture explores the systemic function of general principles in international law in light of the ongoing work of the ILC on general principles of law and recent practice of international courts and tribunals, such as the Climate Change Advisory Opinion of the International Court of Justice from 2025. In its first part, the lecture examines the ILC’s approach to the systemic function of general principles and comments of states on the ILC’s work. In its second and third part, the lecture discusses the two main features of the systemic function of general principles, namely their contribution to inter-norm and inter-systemic coherence in international law. All general principles potentially fulfil a systemic function by their gap-filling role and inter-systemic communication through Article 38(1)(c) ICJ Statute. Several general principles have a systemic pull in inter-norm contexts as interpretative guidelines and inter-norm harmonisers and coordinators. In the relationship between different (sub)orders of international law (including European law and national legal orders applying international law), several principles provide for ‘hinge’ mechanisms and inter-system harmonisers which open legal (sub)orders to one another, and integrate them into (relative) unity, while others serve as inter-system coordinators or mechanisms for conditional closure of legal orders. This means, all general principles have a systemic function, whereas certain principles have more direct systemic function by virtue of their normative content. Through their systemic function, general principles contribute as a central cohesive force furthering international law’s character as a legal and (relative) unitary system. This system is characterized by a complex and dynamic interplay between a plurality of legal norms, orders, and sub-orders, including national legal orders, through systemic principles of openness, coordination, and conditional closure.

Chair: Prof Campbell McLachlan

This lecture was given on 6 February 2026 and is part of the Friday Lunchtime Lecture series at the Lauterpacht Centre.