The Legacy of International Law: Sources

Author: Pankhuri Agarwal, Research Associate

Theories as to the Origin of International Law     

Rules and norms of any legal system derive its authority from their authentic and certain sources. The source of domestic legislations can be legitimated from the mechanical system of constitution, legislature, executive and judiciary which effectuate such laws backed by sanctions. The arena becomes dwindled in the international scenario for the deficiency of specific codified text, body or institution for the purpose. Many raised their eyebrows upon its authority due to complete uncertainty about the origin of International Law. The doctrine of positivism teaches that International Law is the sum of rules by which states have consented to be bound, and that nothing can be law to which they have not consented to be bound1. The positivists believe that International Law can in logic be reduced to a system of rules depending for their validity only on the fact that states have consented to them2. Anzilloti, Triepel, and Oppenheim, the proponents of ‘consent theory’, believe that the states are bound to follow customary rules of International Law because they have given their implied consent for its acceptance3. This theory is untenable for when a rule, formulated by an impressive number of acts of consent emerges as a customary rule, it becomes as such, a rule of law applicable to all, regardless of whether a state accepts or rejects it thereafter4. If consent is all that required then custom will be another name for unwritten treaties5. There are rules which are applicable on states even though they had not given their consent for them. The theory breaks down in the case of a new state being admitted to the family of nations becomes bound by the body of rules in force without expressing its consent thereto except for the customary law where again all nations expect the new state to comply with the existing rules, thus leaving no choice for that new State6. According to Article 2(6) of the UN Charter, the Organization shall ensure that non-Members also act in accordance with its principles7. The positivists restrict the sources of International Law only to customs and treaties. This view is unsustainable in light of the Article 38 of the Statute of the International Court of Justice.

International Court of Justice: Article 38

While the debates were on the peak, the commendable job of International Court of Justice in lieu of specifying the methodological approach to the disputed before it, Article 38 has been construed as giving the direction to the definition of sources of International Law. It identifies five sources, which can be classified under two broad categories:-

A. Formal Sources: (What is the Law?)-

a. international conventions, whether general or particular, establishing rules expressly recognized by the contesting states;

b. international custom, as evidence of a general practice accepted as law;

c. the general principles of law recognized by civilized nations;

B. Material Sources: (Where the Law is?)-

d. subject to the provisions of Article 59, judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law.

The present discussion aims to comprehend the different sources of International Law in light of their content, purpose, and validity and applicability.


The Article does not mention the term ‘treaty’ but, the same has been deduced from the term ‘conventions’. There is a rule of customary International Law of pacta sunt servanda which requires all States to honor their treaties8. The scholarly analysis and experiences has divided treaties into two types: a) traite lois, b) traite contracts. The former being the multi party treaty bears the law making characteristic and the later tends to bear the contractual feature as it is between relatively few parties. The ‘law making treaties’ may be of two kinds:

a) enunciating rules of universal International Law;

b) laying down general or fairly general rules9.

The traditional perception of the treaty being only restricted to its parties, now needs to be modified with the inclusion of the modern treaties which

1) establish a special international regime or

2) establish an international organization.

A good example is the Vienna Convention on the Law of Treaties, 1969. Less than half the States in the world are parties to it but every court which has considered the matter has treated its main provisions as codifying customary law and has therefore treated them as applying to all States whether they are parties to the Convention or not. The law making treaties have the tendency to merge into the customary International Law and hence enjoys the preferential treatment over the customs.  Treaties are not intended to derogate from customary law, and a treaty which seemingly modifies or alters established custom should be construed so as to best conform to, rather than derogate from, accepted principles of International Law10. A treaty will not however prevail over prior customary law if the latter is jus cogens11. The perfect example is the Article 53 of Vienna Convention on the Law of Treaties, 196912.


Custom in International Law is a practice followed by those concerned because they feel legally obliged to behave in such a way or due to a feeling that non-compliance would produce legal consequences imposed by other members of the international community13. The factum of a custom can be analyzed in the light of the excerpt by ICJ in North Sea Continental Shelf Case14:

“Although the passage of only a short period of time is not necessarily, or of itself, a bar to the formation of a new rule of customary International Law… an indispensable requirement would be that within the period in question, short though it might be, State practice … should have been both extensive and virtually uniform in the sense of the provision invoked; and should moreover have occurred in such a way as to show a general recognition that a rule of law or legal obligation is involved15.”

Further, the psychological element of custom to be considered as the source of International Law can be understood in following excerpt:

“Not only must the acts concerned amount to a settled practice, but they must also be such, or be carried out in such a way, as to be evidence of a belief that this practice is rendered obligatory by the existence of a rule of law requiring it16.”

The opinion juris or belief that a state activity is legally obligatory, is the factor which turns the usage into a custom and renders it part of the rules of International Law.

General Principles of Law Recognized by Civilized Nations

Mere presence of certain treaty obligations and customs creates a tricky situation for the International Courts to decide variety of issues involved in a dispute. This creates non liquet situation and thereby the gaps were resorted to be filled through referral to the general principles of law recognized by civilized nations. The general principles are those which are common to the major legal systems of the world for example, the civilian legal system, the common law system and a hybrid system17. At this juncture, the intricacies involved due to overlapping of equity and general principles lead to an assumption that equity might be a source of law. But the closer analysis of the proposition unveils the fact that equity in itself cannot be a source of law for it does not contribute to substantive law, however it can, nevertheless, affect the way substantive law is administered and applied18.

Judicial Decisions

Judicial decisions may be applied subject to the provisions of Article 59 which mandates that the decision of the court has no binding force except between the parties and in respect of that particular case. It must be noted that though ICJ does not prescribe the compulsory rule of stare decisis, but the court in normal parlance owing to the jurisprudential concept of ‘legitimate expectation and certainty has tried to follow its past decisions to the extent possible and applicable. The non exclusion of the rulings of the national court in Article 38, national decisions can be used as a persuasion while the international judgments being delivered by ICJ. There are two ways in which the decisions of the state court may lead to the formation of rules of International Law19;

a) decision may be treated as weighty precedents, or even as binding authorities

b) decision dictate the formation of custom leading directly to the growth of customary rules of International Law.

Unfortunately, the biasedness towards the powerful developed countries is being showcased for the decisions of US, UK etc are given primary importance. Writings are a subsidiary means of determining what the law is on a certain issue at a particular point in time and have a continuing role to play given the absence of stare decisis in International Law20.


The above direction as to the definition of International Law though exclusively stated in the ICJ, the experts have also included other aspects within the ambit of sources of International Law. Acts of International Organizations forms soft law for the purpose of International Law whereby the non-legally binding international instruments are collected in the written form. Some examples of it are: Universal Declaration of Human Rights, 1948, the Charter of New Paris for a New Europe, United Nations General Assembly Resolutions. Regional organizations like Council of Europe, The European Union, The Organization of American States, and The African Union represent what a particular regional grouping of States consider to be the law. The International Law Commission, a subsidiary organ of the General Assembly was established in 1946 with the task of progressive development and codification of law according to Art.13 of the UN Charter. The article 15 of Statute of the International Law Commission states that “the expression “progressive development of International Law” is used for convenience as meaning the preparation of draft conventions on subjects which have not yet been regulated by International Law or in regard to which the law has not yet been sufficiently developed in the practice of States. Similarly, the expression “codification of International Law” is used for convenience as meaning the more precise formulation and systematization of rules of International Law in fields where there already has been extensive State practice, precedent and doctrine.” Jus cogens is a body of peremptory principles or norms from which no derogation is permitted and which may therefore operate to invalidate a treaty or agreement between states to the extent of the inconsistency with any of such principles or norms21. Article 53 of Vienna Convention on Law of the Law of Treaties is a perfect example of it. The Article 38 of ICJ in absence of any such authoritative pronouncement has assumed so much of importance that the sources are being preferred in the hierarchical form as prescribed in it, even though no such provision or clause is present to that effect. The tremendous horizontal and vertical expansion of International Law dispels the aura of doubts as to its legality and authority, serving the greater purpose behind the institution of International Law. The International Criminal law and International Humanitarian law have emerged as separate branches of International Law for the protection of the humanity. The silence as to the repeated questions of the sources of International Law will be applauded for then the larger humanitarian interests can be served better.

  1. Andrew Clapham, Brierly’s Law of Nations: An Introduction to the Role of International Law in International Relations, Oxford University Press, 7th ed., 2012, p. 49. []
  2. Joseph Gabriel Starke & Ivan Anthony Shearer, International Law,  Butterworths Law, 1st ed., 1994 []
  3. David J. Bederman, Spirit of International Law, University of Georgia Press, 2002 []
  4. Bernard Kishoiyian, The Utility of Bilateral Investment Treaties in the Formulation of Customary International Law, 14(2) Northwestern Journal of International Law & Business, 1993, []
  5. Ibrahim F.I. Shihata, The Treaty as a Law-Declaring and Custom Making Instrument, 22 Revue Egyptienne De Drorr International  51 (1966). []
  6. S.K.Verma, An Introduction of Public International Law, PHI Learning Pvt. Ltd., 1998. []
  7. Repertoire of the practice of the Security Council, United Nations, []
  8. Christopher Greenwood,  Sources of International Law: An Introduction, United Nations, []
  9. J. G. Starke, Introduction to International Law, Butterworths Law, 10th  ed., 1989 []
  10. Rebecca Wallace & Olga Martin-Ortega, International Law, Sweet & Maxwell, 6th ed. []
  11. League of nations Official Journal (1920), Sp. Supp. No. 3, p. 45 []
  12. Article 53: “A treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general International Law” []
  13. supra at 10 []
  14. I.C.J. Rep. 1969, p.3 []
  15. ibid []
  16. Military and Paramilitary activities in and against Nicaragua (Nicaragua v The United States) (Merits) I.C.J. Rep. 14, p. 98. []
  17. supra at 10 []
  18. ibid. []
  19. supra at 9. []
  20. supra at 10. []
  21. E.Suy, The Concept of Jus Cogens in Public International Law, 1967 in, Lagonissi Conference on International Law, Papers and Proceedings, Vol. II: The Concept of Jus Cogens in International Law, (Geneva 1967). []