Abstract

Insights from experimental psychology and economics have rarely been applied to the study of international law and never to the study of international legal theory. This article applies them to socio-legal international theory that has grosso modo two important background paradigms with several variants: rationalist and constructivist. In both paradigms, the interest in understanding and explaining international law by uncovering causal mechanisms in international cooperation and compliance and in asking how cooperation is sustained in a system as decentralized as international law is paramount. In both, fundamental assumptions regarding the behaviour of actors are made. However, regardless of the theoretical standpoint, both fall short of experimental evidence about their behavioural assumptions. The article uses experimental evidence provided by public good games as a conceptualization of how social order is constructed and upheld in systems without central authority such as international law. It aims to illuminate the behavioural basis of important building blocks of international cooperation and law by discussing the preferences of states and strategic interaction, reciprocity, sanctions, communication and trust as well as consent and legitimacy, reflecting on what the experimental insights teach us on the assumptions of rationalist and constructivist approaches to international legal theory. These experiments are one means to test behavioural assumptions in international legal theory.