This case study analyzes the process of building legitimate supranational systems centered around the English School of International Relations theory and the transformation of the European Union. The School's key concepts of international and world society, and the three different interrelationships among them, yielded three ideal-type supranational systems each with a different basis of legitimacy: culturalist, communitarian, and moralistic. These ideal-types were then read against the debate held at the Convention on the Future of Europe (2002-2003), tasked with the drafting of a Constitutional Treaty, to determine which among the three best reflected the process of establishing a supranational system in practical terms. The study concluded that the moralistic ideal-type found within the English School theory was the best in helping us understand cases like the European Union
