For if in fact we find that there exists among states a given form of international authority, the sovereignty of states is to that extent limited, and it has just that extent which the rules allow. Hence we can only know which states are sovereign, and what the extent of their sovereignty is, when we know what the rules are; just as we can only know whether an Englishman or an American is free and the extent of his freedom when we know what English or American law is.

H. L. A Hart, The Concept of Law, loc. 522