Chapter one starts from my embarrassment when teaching sources of international law. Following conventional wisdom, I inform students that international law is grounded on a limited set of sources. However, at some point, I also have to explain that it is possible for new sources of international law to emerge. How is this possible, given that international law is grounded on a limited set of sources? I try to deal with this uneasiness by comparing discourses on sources to rituals that prevail in what I call "cyclical societies," organized around the belief in the eternal return of transcendental ideas, acts or events. To apply sources, I argue, is to perform a double act of repetition. First, historically contingent events are turned into manifestations of pregiven and repeatable categories. Second, sources are used as placeholders for something that will always escape positive international law: the foundational categories that underlie the sources of law. These foundational categories, I argue, work somewhat like celestial Gods in cyclical societies: Most of the time they stay dormant and aloof, but they can always be called upon in exceptional times.