International Law in the Best of All Possible Worlds: An Introduction to G.W. Leibniz’s Theory of International Law

Abstract

Today, the contribution by Gottfried Wilhelm Leibniz (1646–1716), the last ‘universal genius’, to the theory of international law is nearly forgotten. Leibniz was a lawyer by training (later in life holding prestigious positions such as Reichshofrat), and he acted as a diplomat and political advisor to the Duke of Hanover. His engagement with legal practice distinguishes Leibniz from other philosophers. Always looking for intellectual synergies, Leibniz integrated his knowledge of (positive) law into his legal theory. Leibniz provides the rare combination of an international legal theory which is both grounded in his metaphysics and natural law theory and inspired by his extensive study of the positive international law of his time (Leibniz was the first to systematically collect and analyse historical international treaty law). This article introduces Leibniz’s theory of international law by outlining the different conceptual layers of his notion of ius gentium, by explaining the functions of natural law for positive international law and by showing how natural law can shape the substance of international relations. The three ‘takeaways’ from Leibniz for contemporary international legal theory are the idea of ‘optimizing pluralism’, his ideas on synergies between ‘theory’ and ‘practice’, and, finally, his insistence on treating law as ‘legal science’.