Andreykiv A. The role of international judicial bodies in formation and realization of customary international law

The thesis explores the role of international judicial bodies in the process of formation and realization of customary international law. Customary international law, being general practice accepted as law, is formed by the instances of conduct that are coupled with opinio juris. It was found that the official definition of custom as a source of international law has institutional nature and is contained in the provisions of the Statute of the International Court of Justice. Thus, the understanding of custom as the form of law and as a rule, which establishes the binding behavior of the subjects of international legal relations, can be possible though the activity of judicial bodies. It is worth mentioning, that according to general practice new states cannot arbitrarily choose legally binding rule of customary international law, as they have the responsibility to abide by the all customary rules, which were established before the creation of a state. Special attention is paid to the psychological element of international custom (opinion juris), which has a major role in cases of absence of repetitive practice in international relations on existence of a certain international custom. It is important to note that the party, which applies to international judicial body and substantiates its position by customary international law rules, has to provide credible evidence that this rule is of customary nature. International judicial bodies in turn assess legal positions provided, acknowledges the existence of customary rule elements needed and decides on its application. International judicial bodies cannot recognize customary nature of a rule by any other consideration. The practice of parties to a treaty (among themselves) is likely to be chiefly motivated by the conventional obligation, and thus is generally less helpful in ascertaining the existence or development of a rule of customary international law. Such practice is normally just that, sometimes serving as a means of interpretation of the treaty under the rules set forth in article 31 (3) (b) or article 32 of the Vienna Convention on the Law of Treaties. The legal effect of rules of customary international law mainly depends on consent of the state, which can be expressive or tacit.