Rational Choice or Deliberation? – Customary International Law between Coordination and Constitutionalization

Rational choice approaches to customary international law have gained in prominence in recent years. Although becoming increasingly sophisticated, they are not able to explain all phenomena of customary international law. This contribution claims that there are two different types of unwritten law in the international order. On the one hand, we have the traditional customary norms, which are identified by observing patterns of state conduct and a related opinio iuris. These norms may very well be described by rational choice approaches, which primarily observe under which conditions we may find stable patterns of behavior. However, there is, on the other hand, a different category of norms that functions in a different manner. These norms concern either human rights or public goods and can be considered as the principles of the international legal order. Their function is not to stabilize already existing behavioral equilibria, but to shape international relations in a positive way. They are not past-oriented, but future-directed. Therefore, it is the thesis of this contribution that a deliberative approach is more suitable to explain the role of these principles in the international community.