Rules or principles must be accepted by the states as legally binding in order to be considered rules of international law. Thus, the mere fact that a custom is widely followed does not make it a rule of international law. States must also view it as obligatory to follow the custom, and not believe that they are free to depart from it whenever they choose or to observe it only as a matter of courtesy or moral obligation. This requirement is referred to as opinio juris. Some criticism against customary international law is directed at its subjective character and its inconsistency.
States vary greatly in their opinions and interpretations of issues regarding international law.
Thus, it is almost impossible to find enough consistency among states to draw a customary international rule from general practice. In addition, even if one state or judge finds that a practice is a rule of customary international law, another decision maker might reach a different conclusion. Altogether, the process of establishing rules of customary international law is lengthy and impeded by today's fast-changing world. Conventions and Treaties Conventional international law includes international agreements and legislative treaties that establish rules expressly recognized by consenting states. Only states that are parties to a treaty are bound by it.