Concept and Process of Formation of the Subjective Element of the Customary Rule (opinion juris) of International Law

INTRODUCTION. Customary international law is the oldest source of International law and has been its main source for centuries. However, even in our time, the importance of custom in International law is preserved – besides and on par with international treaties; this is the other type of its legal norms. The main difference between the two kinds of norm is the unwritten form of custom, but customary and treaty norms have equal legal force.

MATERIALS AND METHODS. The documentary basis of the study is international treaties and international customs, resolutions of the UN General Assembly, Statute of the International Court of Justice and its jurisprudence, reports of the International Law Association. The theoretical basis of the article is the works of scholars of international law. The methodological basis of the study is general and particular scientific methods of cognition.

RESEARCH RESULTS. The research in the article leads to a conclusion that comprises a definition of international custom, and this is the formulation of it as applicable law in cases before the International Court of Justice: “international custom, as evidence of a general practice accepted as law” (Art. 38 (1) (b) of Statute of the Court). According to this definition, the customary legal rule contains two elements: objective, also material the practice of States, and subjective – the conviction of States that this practice is obligatory, i.e. law. It has been established in International law that the subjective element is termed by the Latin expression “opinio juris sive necessitates” (opinion of law or necessity), and most often the subjective element is briefly called only “opinio juris”. The research reveals as its result that by its nature opinio juris represents a conscious, intentional attitude towards State practice. The will of the State has external manifestations – the consent, acceptance, recognition and conviction of the State.

DISCUSSION AND CONCLUSIONS. The main conclusions of the research relate to the question of the formation of opinio juris. This formation is a process that is integrated: it simultaneously forms the practice of States and the opinio juris towards it. Opinio juris does not have an autonomous stage or process of formation, nor is it formed only after the practice of the customary law rule has been completely formed. The conclusion from the integrated process is that each act of the relevant practice, which is the same as the previous one, but also as the next one, helps to form the belief that this is the only, and therefore obligatory, manner to perform the practice. Conversely, States' belief that a given practice is obligatory motivates them to perform only that practice.

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