In this study, the Italian philosopher Sergio Cotta offers a brilliant rational defence of the necessity of natural law and a detailed criticism of the reductionist view of the doctrine of legal positivism, which views natural law as useless. Cotta begins his analysis by pointing out the legitimacy of the function performed by natural law as a "normative rule" for positive law, overcoming the "naturalistic fallacy" which marks the positivist stance. In the second and third sections of the study, Cotta compares the theory of natural law with the theory of positive law to clarify their congruity as two "species" belonging to the genus "law", which share the same logical structure of norms but differ as to the source of obligation. In the fourth section of the study, Cotta draws attention to the dilemma that legal positivists encounter when they build the idea of human rights on temporary, contingent foundations, and to natural law's advantage in overcoming this dilemma by establishing the legitimacy of these rights in light of natural reason. In the final section of the study, Cotta discusses the question, "Why should we abide by the norms of positive law?", answering that the source of this obligation goes beyond the boundaries of the world of positive law and enters the realm of natural law. The norms of positive law become binding if they are justified, and this justification comes from natural law. Cotta finds in this simple yet profound idea a suitable foundation for rejecting the contradiction between natural law and positive law and creating harmony and continuity between them.