Lachs, Manfred Keywords: Multilateral treaties | Law of treaties | Mots clefs: Traités multilatéraux | Droit des traités | ABSTRACT In his course, Manfred Lachs analyzes the circumstances in which the changes made by multilateral treaties in the institutions inherited from bilateral treaties have taken place, both in substance and in form. Indeed, the author notes that these two elements are integrally linked to each other. The contradiction between these two elements, or their harmonious cooperation, ultimately de…