ABSTRACT
I Lucas, in agreement with all medieval legal philosophers, derives the notion of law from an extra-legal premiss-that is, from justice. It is true that this derivation was already to be found in the Roman texts, in which, however, it was a figurative phrase rather than a workable principle. Neither the Roman jurists nor the Glossators dwelt on the significance of this idea to any appreciable extent. Lucas, the Post-Glossator, deals with this conception theoretically, examines the idea in all its legal aspects, and demonstrates its practical application and its effects on the various branches of law. Indeed, the derivation of law from justice becomes an intrinsically fruitful principle and the foundation upon which his jurisprudential system is erected.
