the consensual foundation for customary law fails to explain why custom applies to all States, including newly independent States, regardless of their culture or political system. State practice and opinio juris Customary rules have evolved through a long historical process through which State practice and recognition of those practices within the international community have crystallized. The underlying theory is that customary law is founded upon the implied consent or general acceptance of the international community. A common usage can become a customary rule where there has been a sufficient recurrence or repetition of an act and can be proved by reference, for example, to diplomatic relations between States, the practice of international organisations, national laws and the decisions of national courts and administrative practices. In this sense, customary laws are inferred from repeated and consistent acts. In addition to general State practice, international courts have required that the creation of custom must satisfy a psychological aspect described as opinio juris and defined as the “mutual conviction that the recurrence is the result of a compulsory rule”. The test of opinio juris is circular in the sense that a State must have believed it was bound by the rule before the rule could be binding upon it, raising the question of the time at which any usage can became custom. Moreover, it is by no means clear how the subjective belief in an obligation can be demonstrated in the case of a State. The requirement that there be evidence of opinio juris has led to much judicial and academic debate. It remains helpful, however, to use the concept of opinio juris to distinguish custom from an act that is followed for reasons of comity or courtesy. The court in West Rand Central Gold Mining Company v R ([1905] 2KB 391 at 407) held that opinio juris must be proved by satisfactory evidence that the alleged rule “is of such a nature, and has been so widely and generally accepted, that it can hardly be supposed that any civilised State would repudiate it”. The International Court in the North Sea Continental Shelf Cases (ICJ 1969,3) argued that: “Not only must the acts concerned amount to a settled practice, but they must also be such, or be carried out in such a way, as to be evidence of a belief that this practice is rendered obligatory by the existence of a rule of law requiring it. The need for such a belief, ie the existence of a subjective element, is implicit in the very notion of the opinio juris. The States concerned must therefore feel that they are conforming to what amounts to a legal obligation.” 32