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  • Tanya Varsheny

Resolving the Disjunction of Treaties, Customs and International Judicial Decisions

Author's Information: This paper is written by Tanya Varshney, 4th-year, B.A. LLB. (Hons), Jindal Global Law School, O.P. Jindal Global University.


Doctrine of sources in the jurisprudence of international law has been the subject of various scholarly works and even international judicial decisions because of the availability of differing provisions and rules for the international courts to follow. Hierarchy of sources in the jurisprudence of international courts has become a crucial question to answer especially when the sources such as treaty law, conventions and customary international law differ in opinion. This paper attempts to outline the nature, identification and the legitimacy of the sources of law and authority in the jurisprudence of International Courts. This paper further highlights the challenges faced by the International Courts while interpreting the overlaps and departures amongst the primary sources of law; arguing for relevance of a hierarchy in the doctrine of sources to resolve this disjunction.

Horizontal Sources in International Law

Article 38(1) of the Statute of the International Court of Justice recognizes international conventions, international customs, general principles of law recognized by civilized nations as the primary sources of law, and judicial decisions as well as teachings of highly qualified publicists of various nations as subsidiary means for the determination of rules of law.

The primary concern regarding Customary International Law is the question of when can practice be regarded as a custom binding on states, and the ways in which customary law can evolve with changing times. It has been settled by the decisions of International Court of Justice and various scholarly works that customary international law gets derived from state practice and opinio juris[1]. An important aspect of customary law as mentioned in the Asylum case[2] is “constant and uniform usage practiced by States”. There must be sufficient uniform practice which has existed in continuity, which creates rights and duties for the States involved, and therefore it is imperative that these practices are not uncertain and contradictory[3]. Moreover, besides the requirement of a uniform and continuous practice, there must be an obligation upon the states to act according to such practice which constitutes the second element of customary law known as opinio juris. In the Lotus case[4], the Permanent Court of International Justice observed that for the recognition of custom, the state’s must have a duty to act according to that practice. For instance, abstention would give rise to the recognition of international custom if the states had an obligation or conscious duty to abstain, otherwise it would merely remain practice.

Treaty law, on the other hand, has a resemblance to a contract as an essential element for a treaty to be binding is the State’s consent or ratification of the treaty. Treaty law would not be binding upon the States who are non-signatories to the treaty. This is the rule of pacta teriis nec nocent nec prosunt, also incorporated in Article 34 of the Vienna Convention which provides that “a treaty does not create either obligations or rights for a third State without its consent.” Despite this principle, the International Courts have interpreted that treaties may apply to non-signatories where treaties create customary international law.

Disjunction of Treaty Law and Customary Law

Since customary law and treaty law have been regarded as the primary sources of law in the same horizontal plane, it becomes important to examine questions such as whether treaties are merely reflective of customary international law and how the International Court of Justice should interpret laws in situations where treaties might conflict with customary international law. In the North Sea Continental Shelf case[5], the International Court of Justice remarked that even the non-parties to the treaty will be bound by its provisions if the treaty reflects customary international law. The provisions of a treaty exhibiting uniform state practice “of a fundamentally norm creating character” and opinio juris generate customary law binding even on those States who have not consented to the original treaty. D’Amato highlights the danger of treaty provisions entered into by a small number of states creating potential customary law binding upon all States, including the States who have not consented to be governed by the said treaty[6]. One might raise the question that whether this makes the element of State consent redundant if ‘norm-creating provisions’ could be binding on non-consenting States.

Another problem that arose in the Nicaragua case[7] was if treaty law and customary law are identical, whether the treaty ‘subsumes and supervenes’ the customary law? The Court answered this in the negative and remarked that where treaty law and customary law were identical, the customary international law will be applicable separately and will continue to exist independent of treaty law. Therefore, even if the States entered into multilateral treaties, the Court could still rely on principles of customary international law. The Court also highlighted that applying customary international law where it diverged from the provisions of multilateral treaties would not render the judgement ‘insusceptible of compliance or execution’. The rationale provided by the Court was that in the dispute between Nicaragua and USA, both Article 51 of the United Nations Charter and the customary international law governing the use of force were derived from a common fundamental principle in international relations.

Baxter notes this disjunction between treaty law and customary international law with respect to rights and duties of non-party States by highlighting the difference between treaty law departing from custom and treaty law which is declaratory of existing customary laws. The ideal case and the superior source of law, according to him, is when treaties are declaratory of existing customary laws as it is representative of the ‘will of the States, free of ambiguities’. However, he also notes that this is rarely the case, as often, treaty laws diverge from customary international law in some respects.[8] The question that arises then is whether the primary sources of law are truly horizontal or whether there exists a hierarchy within the primary sources. If customary law can prevail over treaty law where the provisions are identical, how does one resolve the challenge of ‘progressive development’ and the negation of State consent?

Doctrine of Sources – Need for Legitimizing Authority in International Law Jurisprudence

It appears from the Court’s opinion in Nicaragua that customary international law is superior to treaty law, however, the question of when does a practice become customary international law is uncertain and open to the interpretation of International Courts. A problem which is encountered with customary laws is that since they are primarily concerned with past practices of the State, contemporary changes or ‘progressive development’ can only be incorporated through codification of customs in treaties. Hence, even if the treaty is meant to be identical to a custom, there will be some amount of divergence and disjunction amongst the international conventions, international customs and general principles of law. Therefore, if the sources of law are kept in a horizontal chain there will be ambiguity in the jurisprudence of International Courts. For instance, in the Barcelona Traction case[9], the Court relied on a mixture of sources including treaties, general principles of law recognized by nations, arbitral jurisprudence and previous decisions of the court[10].

Michael Akehurst recognizes the uncoordinated system of governance in International Law due to the horizontal structure wherein no source of law is superior to the other. Unlike municipal laws where there is a superior constitutional text governing the legislations made by the national governments, no such legal body exists in the sphere of public international law. Moreover, there is no hierarchy amongst the International Courts.[11] Thus, identifying a hierarchy in sources of international law becomes a burdensome task. Harlan Grant Cohen identifies this problem as a paradox in the doctrine of sources and presents an alternative solution to rethink the doctrine of sources centralized on norms and opinio juris. Unlike Baxter, who is more inclined towards a hierarchy of treaty law, Cohen emphasizes upon the importance of state recognition and internalization of rules. According to him, the provisions of treaty law should be ‘judged by the internalized norms supporting them’[12]. The reasoning behind his thesis is that although states enter treaties with free will, they don’t generally comply with the provisions. If the legal rules governing the States are internalized, this will ensure a uniform compliance to the international legal system. However, Professor Cohen’s solution to rethinking about doctrine of sources doesn’t account for inconsistency in recognition of rules amongst the powerful states and the smaller states.

Furthermore, protection to peremptory norms of general international law is given under Article 53 of the Vienna Convention under the principle of jus cogens which provides that “a treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general international law”. This ensures that treaty law entered into by States is not arbitrary or a threat to international peace or security. Although, what constitutes a peremptory norm is uncertain, Article 53 defines it as “a norm accepted and recognized by the international community of States as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law having the same character.”


It is submitted that there is a need for a legitimizing authority in international law for a uniform system of governance. Although customary law and general principles recognized by states present a compelling argument for compliance of states, the hierarchy of treaty law is a better solution to resolve the overlaps and departures in the primary sources of law. The argument presented is not that international customs should not be regarded as a primary source of law, but instead when treaty laws and customary laws differ in opinion, the Courts should give more importance to treaties which have been drafted over recent years with the consent and ratification of States unlike customs which have developed over decades of outdated state practices[13]. Moreover, the states that are non-party to the treaties should not be governed by the provisions of the treaty law merely because the Courts interpret it to be identical to international customs. If the treaty law is rendered binding upon the non-consenting States, it essentially negates the requirement of free will of the states and could lead to potential danger in international politics.

[1] Shaw, M. N. (2017). International Law (6th ed.). Cambridge, United Kingdom: Cambridge University Press.

[2] Colombian-Peruvian Asylum case, Judgment of November 20th 1950: I.C. J. Reports, 1950, pp 266.

[3] Fisheries case, Judgement of December 18th, I95I: I.C. J. Reports 1951, p 116.

[4] S.S. Lotus (Fr. v. Turk.), 1927 P.C.I.J. (ser. A) No. 10 (Sept. 7)

[5] North Sea Continental Shelf, Judgement, I.C.J. Reports 1969, p. 43.

[6] D'Amato, Anthony, "Treaties As a Source of General Rules of International Law" (1962). Faculty Working Papers. Paper 120.


[7] Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States of America), Merits, Judgment, I.CJ. Reports 1986, p. 98

[8] R. R. Baxter, “Treaties and Custom” (1970) 129 Recueil des Cours 25, 64.

[9] International Court of Justice, Barcelona Traction, Light and Power Company, Limited; Judgment of 5 February 1970, I.C.J. Reports 1970, p. 3.

[10]Supra, see 8

[11] Michael Akehurst; The Hierarchy of the Sources of International Law, British Yearbook of International Law, Volume 47, Issue 1, 1 January 1976

[12] Harlan G. Cohen, Finding International Law: Rethinking the Doctrine of Sources, 93 Iowa L. Rev. 65 (2007), <>

[13]Supra, see 6

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