Abstract

Hans Kelsen’s application of his Pure Theory of Law to international law was supported by two key theoretical assumptions. According to the systematicity assumption, present in Kelsen’s work between 1920 and 1960, legal cognition constituted international law as a unified system, grounded in a presupposed basic norm. According to the evolutionist assumption, prominent between 1934 and 1945, social institutions underwent a teleological process of evolution, so that international law could be expected to recapitulate the development of domestic legal systems. This paper analyses the evolutionist model, identifying what Kelsen considered to be the minimum content of a legal order and the characteristics of the earliest legal orders, and showing how his analysis of international law followed the model. It then reviews the systematicity assumption and the difficulty of applying it to international law, particularly with regard to the basic norm. These difficulties, and some potentially unsettling implications of the evolutionist assumption, are discussed with reference to the broader history of Kelsen’s theoretical work. In conclusion, the paper argues that the same drive for certainty that led Kelsen to champion these models led him to abandon or downplay them after 1945, discounting the insights that they could offer him – and us.