The political constitution of the European polity has become strained in recent years by insistent pressures on its institutional capacity to resolve social problems. The article examines the EU's polity crisis in the context of the development of a distinctive modern conception of secular constitutional authority, focused on the ideal of sovereign self-determination. As the work of Neil MacCormick illustrates, the EU provides a radical challenge to the on-going capacity of the concept of sovereignty to provide a framework to address problems of legitimacy. The article explores the nature of this challenge, its historical context and its consequences with reference to debates over the nature of constitutional pluralism. It sets out a path to the renewal of the European constitutional debate through a re-consideration of secular constitutional authority and the necessity of its connection to the idea of sovereignty. The article seeks to re-engage in the task of ‘questioning sovereignty’.