The use of state practice and opinio juris to identify customary international law has increasingly come into question. Yet this is a foundational question of the concept of law. The chapter draws from Herman Dooyeweerd’s Encyclopedia of the Science of Law to explain CIL. He distinguishes the jural aspect from all other aspects of reality, accounting for the former’s internal structure as it is interconnected with that of fourteen other aspects, in a complex web of analogies. The Encyclopedia examines the nature of the jural dimension through three interrelated pillars. The jural aspect is one of the irreducible yet interconnected universal multidimensional modes or aspects of reality. Through it, the second and third pillars – entities and enkapsis – are viewed and understood as legal phenomena. Entities build pluralistic legal ontologies that exhibit differentiated responsibility and differentiated integrity. Enkapsis is the complex intertwining of formal and material sources. In ‘legal enkapsis’ different material sources display a mutual interrelationship that binds and limits without altogether cancelling one another, a process described as ‘inter-legality’ in contemporary literature. It combines the two pillars of his philosophy –modal aspects and entities – into a comprehensive and integrative concept of law, to provide a systematic account of CIL as inter-legality.