This is a translation of a French text, this book asks two core inter-related questions. The first is: how have legal philosophers systematized law, and what types of assumptions have been made in undertaking this task? Second, in what sense is the law a system and how is it maintained as such? In answering the first question the book surveys and analyzes the theories of a number of European legal philosophers and in answering the second, the authors put forward their own theories.