However, in recent times, on account of existence of large number of international treaties between various States, the predominant position of custom as a source of international law is diminished.
International Court of Justice while dealing with the Colombian Peru Asylum case, observed that;
- A party relying on custom must prove that, the alleged custom is binding on the other party; and
- The customary rule relied upon is in accordance with the consent and uniform usage practiced by the State in question.
Thus, the custom has to be established like any other question of fact. A rule of customary law should be established by satisfactory evidence to the effect that, the rule is of such a nature and has been so widely and generally accepted that, it can hardly be supposed that any civilized State will repudiate it.
The customary rule may also develop out of law laid down in a municipal legislation or in a decision of court of law, when it receives recognition from other States. However, as to how much time a practice or usage takes before being recognized as custom depends upon the facts and circumstances of each case.
Usage is an international habit of actions that has not yet received full attention. When a usage becomes well established, it becomes Custom. Practice is the beginning of customary rules which may or may not be fully crystallize into custom.