Since the emergence of international law as an autonomous discipline in the middle of the 18th century, the problem of its foundations has always been a matter of dispute among scholars. It remains a vexata quaestio. The positivist school of thought, which had its roots in the nominalism of William of Occam and the doctrine of State and natural law of Thomas Hobbes, developed rapidly in the pragmatic world of the 19th century by using the methodology of natural sciences. The positivism declared that law as it exists should be analysed empirically, shorn of all ethical elements. Law in the society is the positive law. And the foundation of international law is to be found in and only in the will of states. This article aims to show the limits of the legal positivism. By analysing the metaphysics of Aristotle, metaphysics of the final cause, theory of potentiality and actuality, the article explains why it is useful to turn to the systemic approach in international law.