In accordance with Finnis, the classical naturalists were not involved with giving a conceptual account of legal validity; rather they were involved with explaining the ethical drive of law: “the ideas of pure legislation explain the compulsory force (in the fullest sense of ‘obligation’) of constructive laws, even when those legal guidelines can’t be deduced from these ideas” (Finnis 1980, 23-24).
Whereas he rejected the blurring of regulation and morality, he did give an identical “unified” definition of regulation: “A rule laid down for the guidance of an intelligent being by an intelligent being having power over him.” God and males both make laws so his distinction is between the legal guidelines of God (cause) and people of historical human societies made by political “superiors.” He insisted on distinguishing the idea of (concept of) law from the “science of laws” which needed to do with the criticism (evaluation) of the legislation (c.f. Dworkin’s concept of legislative justice).
Two norms can derive their validity from the identical basic norm, however fail to belong to the identical system as, for instance, in case of an orderly secession whereby a new legal system is created by the legal authorization of one other.
St. Thomas Aquinas, for instance, identifies the rational nature of human beings as that which defines moral regulation: “the rule and measure of human acts is the reason, which is the first precept of human acts” (Aquinas, ST I-II, Q.90, A.I). On this frequent view, since human beings are by nature rational beings, it’s morally appropriate that they need to behave in a way that conforms to their rational nature.