Constitutionalism, Legal Positivism and Natural Law Theory In this paper I present six theses that can be summarised as follows: 1) in contemporary legal theory there are two different versions of "constitutionalism": the positivist and the non-positivist (or post-positivist); the second is superior to the first. 2) This second version (the constitutionalist conception in the strict sense) is based on the identification of two ingredients in the law: the authoritative and the evaluative, and also on giving some priority to the latter. 3) To deny the thesis of the conceptual separation between law and morality does not turn the postpositivist authors into natural law theorists. 4) Nevertheless, in the last century some natural law theorists were shown to have in some respects a more profound vision of the law than that of positivist lawyers. 5) Post-positivist constitutionalism does not defend the "imperialism of morality" but the "supremacy of morality " in practical discourse. 6) The "ideology of separation" and moral scepticism make legal positivism an inappropriate conception in order to understand (and to act in the context of the) law in a constitutional State.