Purely positive law takes its place in a scheme of practical reasoning whose proximate starting point is the moral need for justice and peace.

That is to say: the concretized rule is (morally as well as legally) normative because such normativity is (presumptively and defeasibly) entailed by the (moral) principle that the common good (whose fundamental content is given by the foundational principles of practical reason: 1.1) requires that authoritative institutions take action to specify, apply and enforce some rules on the relevant matters. Social facts make a positive legal rule a reason for action because the desirability of authori