The essay discusses the import of the separability thesis both for legal positivism and for contemporary legal practice. First, the place of the separability thesis in legal positivism will be explored, distinguishing between “standard positivism” and “post-Hartian positivism”. Then we will consider various kinds of relations between law and morality that are worth of jurisprudential interest, and will explore, from a positivist point of view, what kind of relations between law and morality must be rejected, what kind of such relations should be taken into account, and what kind of such relations are indeed of no import at all. The upshot of this analysis consists in highlighting the distinction between two different dimensions of legal validity (formal validity and material validity respectively), and in pointing out that the positivist separability thesis can apply to formal validity only; on the contrary, when the ascertainment of material validity is at stake, some form of moral reasoning may well be involved (and, here and now, necessarily is involved). The essay concludes with some brief remarks on the persisting importance of the positivist jurisprudential project.