The aim of the paper is that of discussing some recent antipositivist theses, with specific reference to the arguments that focus on the alleged incapability of legal positivism to understand and explain the complex normative structure of constitutional states. One of the central tenets of legal positivism (in its guise of ``methodological'' or ``conceptual'' positivism) is the theory of the separation between law and morality. On the assumption that in contemporary legal systems, constitutional law represents a point of intersection between law and basic moral values, antipositivists contrast legal positivism with two main arguments. First, on a more general level, the positivist theory of the separation between law and morality is questioned; then, and consequently, the ``neutrality thesis'' in the juristic study of law is rejected. The author discusses both these antipositivist arguments, and offers a brief defence of methodological positivism.