Customary Law and Treaty Law

During the existence of international legal practice, there has been a plethora of disputes, opinions, and discussions regarding which source of international law is the main one – a treaty or custom. Many scholars and officials have stated that an international agreement should be in favor in this regard, claiming that the formal conventions provide a great extent of certainty and solidity. However, several advantages may be a foundation for the assumption that customary law is more preferred than treaty law. Hence, the mentioned topic might be relevant to discuss as it concerns the essence of international law and may contribute to an in-depth understanding of the phenomena.

Treaty law may be defined as a part of international law consisting of international legal agreements, which indicates an international treaty as the primary source of international law. Treaties were known to the practice of states long before the emergence of international law since, in the relationship of independent entities, the agreement is the most preferred means of a peaceful settlement. With the advent of international law, treaties between states have become legal.

Customary law may be determined as a part of international law that “is composed of all the written or unwritten rules that form part of the general international concept of justice” (Sources of international law, n.d., para. 12). It means that an international custom is considered as the primary source within the scope of customary law.

It is impossible to imagine the existing international legal system without a custom, not only because many branches and institutes consist partly or entirely of customary rules. New rules of customary law continue to emerge in areas where contractual settlement is not possible for various reasons. The peculiarity of international custom as a source of international law is that, compared to an international treaty, it makes it difficult to distinguish between law-making and normative outcome. While an agreement exists in the form of a normative act, the custom is created by the practice of the states and operates in the kind of a norm that establishes this practice.

The actions of countries that shape international customs are the result of the interaction of claims made by states (Customary international law, n.d.). These actions come from their international legal position on specific problems, as well as their active or passive reaction to these claims by other countries. Such legal claims are made in the form of particular actions, unilateral or multilateral acts or statements by states.

It may be assumed that the most appropriate form of external expression of the norms of international law – its generally recognized principles and standards – is the international legal custom. Its main advantage over the international treaty may be identified as follows: customary law is the primary means of expressing universal moral and constitutional values. It might be supposed that the customs of international law have been formed on the basis of the centuries-old historical experience of social relations.

The latter statement contributed to the fact that properties of customary law are independent of the political situation. Such independence leads to a significant level of impartiality in the founding international legal principles. It is a vital aspect of international law that may sometimes be affected by the political interests of an influential actor.

History has shown that most common multilateral treaties have indeed become universal, encompassing a vast number of states with their obligations. However, it should be stated that there is no agreement that has been able to unite all countries. After a relatively short period, the practice of applying these treaties has updated the issues of their amendments and additions. Initially, customs were general beliefs, which acquired the force of norms binding on all states between which relations were maintained.

These were norms so related to the nature and needs of this kind of relationship, that their maintenance seemed inseparable from compliance with these norms. Thus, the international legal custom is the primary source of international law because of the absence of an agreement to which all members of international communication would be parties.

In international law, the topic of imperative norms, just cogens, is of continuing relevance; nevertheless, there are a lot of complex scientific and practical problems. In international scientific and political circles, a common understanding has long been formed of the need for specific universal legally binding rules for international communication (Kadelbach, 2016). However, at the same time, there is no unified position regarding which particular rules of international law are imperative.

Not a single international agreement or a law-forming resolution of an international intergovernmental organization provides a clear interpretation of the category “imperative norm” or at least an approximate list of these norms. Hence, customary law should provide jus cogens as it cannot be canceled by agreement or by tacit consent but can disappear only after the formation of new customary rules of the contradictory ideas.

There are more legal grounds in favor of the jus cogens category itself than in support of its specific content. However, it should be reasonably claimed that for particular provisions of jus cogens, all governments have come to a joint agreement. It applies to norms relating to the use of force by states, self-determination, and genocide. The mentioned aspects firmly exist in the framework of international legal treaties. Nevertheless, international agreements, as one of the main ways to consolidate the norms of international law, cannot adequately cope with the role of an all-encompassing legal instrument. Therefore, as most scholars believe, this burden logically goes to another primary source of international law – the custom.

To sum everything up, three points regarding the issue of why customary law is the better option to apply than treaty law were identified. First, the international legal custom is free of political interests. Second, the international treaty cannot distribute its legal obligation to all countries. Third, it was supposed that customary law should be a provider of imperative international rules as it is more stable and harder to change than treaty law.


Customary international law. (n.d.). Web.

Kadelbach S. (2016). Genesis, function and identification of jus cogens norms. In: M. Heijer & H. Wilt (Eds.), Netherlands Yearbook of International Law 2015. (pp. 147–172). The Hague: T.M.C. Asser Press.

Sources of international law. (n.d.). Web.

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