According to Hart's view of the Social Fact Thesis, then, a proposition P is legally valid in a society S if and only if it satisfies the criteria of validity contained in a rule of recognition that is binding in S. As we have seen, the Conventionality Thesis implies that a rule of recognition is binding in S only if there is a social convention among officials to treat it as defining standards of official behavior. Thus, on Hart's view, "[the] rules of recognition specifying the criteria of legal validity and its rules of change and adjudication must be effectively accepted as common public standards of official behaviour by its officials" (Hart 1994, p. 113).
The idea that a norm that does not conform to the natural law cannot be legally valid is the defining thesis of conceptual naturalism. As William Blackstone describes the thesis, "This law of nature, being co-eval with mankind and dictated by God himself, is of course superior in obligation to any other. It is binding over all the globe, in all countries, and at all times: no human laws are of any validity, if contrary to this; and such of them as are valid derive all their force, and all their authority, mediately or immediately, from this original" (1979, 41). In this passage, Blackstone articulates the two claims that constitute the theoretical core of conceptual naturalism: 1) there can be no legally valid standards that conflict with the natural law; and 2) all valid laws derive what force and authority they have from the natural law.