Sørensen, Max Keywords: Legal principles | Public international law | Mots clefs: Principes de droit | Droit international public | ABSTRACT According to Max Sorensen, the course explains the interrelation of the two factors of stability and evolution that is, in any legal system, the crux of the problems for doctrine and practice that arise. Stability is the essence of the law. Evolution, on the other hand, is the necessary consequence of the changes taking place in the social conditions at the base of the legal sy…