Opinio juris

Opinio juris (from Latin Opinio Juris ) (literally the opinion of law ) is an expression that is used in international law to establish the recognition by law-makers of the rules of conduct as a rule of law or the conviction of subjects of international law in the legal usefulness (validity) of a rule of law.

Opinio juris, or recognition as a rule of law, gives the usual rule of legitimacy, giving it authority and legal force. Without this normative aspect, practice is no more than a usual routine or a simple habit, but not a right ^[1] . To this end, as the International Court of Justice stresses, it is necessary to ascertain whether this or that rule of customary law exists in the opinio juris of states and make sure that this is confirmed by practice ^[2] . In other words, it is necessary that the practice be accompanied by the conviction that it obliges the state precisely as a right .

In practice, this means the recognition by the state of a certain rule as a rule of international law. Such recognition may be explicit or silent. Explicit recognition is fixed in contracts in writing and, as a rule, does not cause the need to find out whether the recognized rule of conduct is a rule of law.

Explicit recognition is carried out most often in the form of an application and is the most preferred form of recognition, since it does not cause questions and disagreements. On this basis, the value of various statements of states for establishing the opinio juris is greater than the value of actual actions. In the case of actual actions, however, there is also a presumption that states commit them on the basis of recognition of their legal obligation. But it is precisely by making a statement that the state unequivocally expresses its point of view ^[3] .

It is more difficult to find out the recognition of a rule of law as a rule of conduct, the formation of which takes place in a silent form. We are talking about international legal custom, which is a repetition of a certain type of behavior (element one, objective), and which should be considered by states as a rule of law based on their conviction that this rule is legally binding (element two, subjective).

The statute on Opinio Juris is enshrined in the Statute of the International Court of Justice and states: “International custom as evidence of general practice recognized as a legal norm” (Article 38 § 1 “b”).

Legal scholars , finding out whether Opinio Juris exists, refer to the declarations of states, acts of international organizations, court decisions, etc.

A typical example of Opinio Juris is the decision of the International Court of Justice of September 25, 1997 on the dispute between Hungary and Slovakia (the Gabcikovo - Nagymaros Project ( Hungary v. Slovakia )), in which the Court, ascertaining whether there is a certain rule of law (Opini Yuris), referred to to the responsible comment of the UN International Law Commission (although this document, as such, is not a source of international law).

Such a logical construction plays an important role in the analysis of already existing rules of customary law. But more problematic is the presence of this design when new normal norms appear. If the practice is not controlled by the norms of customary law, it becomes logical to identify the state’s conviction that it acted legally, creating such a practice. This paradox is resolved to some extent by the concept of "crystallization", according to which the practices and duties of the state evolve together and eventually develop into the law.

No less important than explicit recognition is the direct objection of the state against the emerging norm (for example, in the form of protest). Such an objection (as well as explicit recognition) makes it possible to clearly define the position of the state in the process of custom formation and, accordingly, will indicate its lack of agreement with the emerging norm - opinio non juris ^[4] .