Since the late 1980’s international legal scholarship has been shaken up by incisive anti-foundational critiques as voiced by inter alia David Kennedy and Martti Koskenniemi. Following the tradition of critical legal scholarship, these critiques demonstrated the indeterminacy of foundational legal concepts in international law and the openness and reversibility of international legal arguments. The insights from critical legal scholarship provoked strong and contradictory responses. Some embraced them as tools for emancipation, that could be used to disclose the political agendas pursued in the name of an objective and neutral international legal order. International law, in this view, should be re-politicized. Others, however, regarded critical scholarship as undermining the international rule of law; as a project that may be well-developed in terms of analysis and deconstruction, but also as a project that threatens international law’s independence from politics as well as its ability to civilize conduct in international affairs. Jan Anne Vos’ The Function of Public International Law is an ambitious attempt to transcend the terms of the debate between critical legal scholars and ‘mainstream’ international lawyers about the relation between law and politics. Vos basically accepts the validity of the critique voiced by critical scholarship. In terms not dissimilar to Koskenniemi’s basic concepts in From Apology to Utopia, Vos argues that international legal argument oscillates between two mutually exclusive positions or frameworks. The first is the framework of obligation, which holds that rules of international law restrict a pre-given freedom of states. The other is the framework of authorization, which holds that international law confers upon states the normative power to act. According to Vos both frameworks suffer from the same problem: they cannot be upheld consistently. As a result, international legal argumentation has a tendency to constantly shift from one position to the other, even though both positions cannot be valid at the same time. Vos illustrates the workings of both frameworks in general theories of law, international theory, the sources of international law, the law of international organizations and concepts such as ius cogens and erga omnes.