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 bound ((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.)). 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 them ((Joseph Gabriel Starke & Ivan Anthony Shearer, International Law,  Butterworths Law, 1st ed., 1994)). 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 acceptance ((David J. Bederman, Spirit of International Law, University of Georgia Press, 2002)). 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 thereafter ((Bernard Kishoiyian, The Utility of Bilateral Investment Treaties in the Formulation of Customary International Law, 14(2) Northwestern Journal of International Law & Business, 1993, If consent is all that required then custom will be another name for unwritten treaties ((Ibrahim F.I. Shihata, The Treaty as a Law-Declaring and Custom Making Instrument, 22 Revue Egyptienne De Drorr International  51 (1966).)). 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 State ((S.K.Verma, An Introduction of Public International Law, PHI Learning Pvt. Ltd., 1998.)). According to Article 2(6) of the UN Charter, the Organization shall ensure that non-Members also act in accordance with its principles ((Repertoire of the practice of the Security Council, United Nations, 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 treaties ((Christopher Greenwood,  Sources of International Law: An Introduction, United Nations, 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 rules ((J. G. Starke, Introduction to International Law, Butterworths Law, 10th  ed., 1989)).

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 Law ((Rebecca Wallace & Olga Martin-Ortega, International Law, Sweet & Maxwell, 6th ed.)). A treaty will not however prevail over prior customary law if the latter is jus cogens ((League of nations Official Journal (1920), Sp. Supp. No. 3, p. 45)). The perfect example is the Article 53 of Vienna Convention on the Law of Treaties, 1969 ((Article 53: “A treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general International Law”)).


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 community ((supra at 10)). The factum of a custom can be analyzed in the light of the excerpt by ICJ in North Sea Continental Shelf Case ((I.C.J. Rep. 1969, p.3)):

“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 involved ((ibid)).”

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 it ((Military and Paramilitary activities in and against Nicaragua (Nicaragua v The United States) (Merits) I.C.J. Rep. 14, p. 98.)).”

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 system ((supra at 10)). 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 applied ((ibid.)).

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 Law ((supra at 9.));

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 Law ((supra at 10.)).


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 norms ((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).)). 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.

An Introduction to Sources of International Law

Author: Donia Joevion Fuller, Research Associate

The clearest exposition on what one may consider as a source of law is to be found in Article 38(1) of the Statute of the International Court of Justice (ICJ), which states:

  • The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:

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;

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.

Put succinctly, sources of law fall into four categories, international treaties, customary international law, general principles of law and judicial decisions coupled with teachings of the most highly qualified publicists. This Article aims to show the operation of each source of law and how they may of potential benefit to any international tribunal called upon to settle disputes.

International Conventions and the theory of Pacta Sunt Servanda

The Vienna Convention on the Law of Treaties, 1969 (VCLT) stands as the authoritative position on the operation of international conventions, more commonly called treaties.  The Convention defines a treaty as, “ an international agreement concluded between States in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation ((Article 2 (1) (a) VCLT, 1969)).” Central to the operation of treaties, and arguably in keeping with the notion of State sovereignty is that states may contract themselves to any term; consequently, a treaty may have its own mechanism for enforcement and dispute resolution. In the absence of such clear provisions, the VCLT may act as a guide on how to operate.

The issue of state sovereignty also features in the discourse of why states adhere to their treaty obligations. In this regard, the principle of pacta sunt servanda is of utmost importance. Article 26 of the VCLT stipulates that, “Every treaty in force is binding upon the parties to it and must be performed by them in good faith.” Despite the fact that there is no way to manually coerce states into performing their international obligations as against another state, one must recognize that the operation of international politics is such that economic pressure by one party brought to bear on another may be a viable mechanism to secure compliance. In addition, particularly as it relates to developing countries that rely on aid from the European Union and other international organizations, compliance with human rights treaties such as the International Covenant on Civil and Political Rights features largely in the decision whether or not grants will be meted out to various territories. In recent months, Refugees International (RI), a Washington based international advocacy group for lifesaving assistance and protection for displaced people, urged the Obama administration to withhold assistance to the government of South Sudan over alleged human rights abuses by its army (SPLA) in Jonglei state. Similarly, the European Parliament threatened to halt funds to Egypt, citing Port Said death sentences, human rights violations, and lack of political consensus in Egypt.

Customary International Law- Opinio Juris and State Practice  

By virtue of being a treaty itself and having been widely accepted by the international community as the authority on the interpretation of treaties, the principles enshrined in the document illustrate the operation of customary international law ((Frederic L. Kirgis, “Reservations to Treaties and United States Practice,” ASIL Insights (May 2003), available at Customary international law as defined by the ICJ Statute is a general practice accepted as law. The ICJ itself stated in the North Sea Continental Shelf Case: “It is of course axiomatic that the material of customary international law is to be looked for primarily in the actual practice and opinio juris of States ((ICJ, Continental Shelf case (Libyan Arab Jamahiriya v. Malta), Judgement, 3 June 1985, ICJ Reports 1985, pp. 29–30, para. 27.)).” This profound statement is taken by many scholars to mean that in order to establish that there is a principle or rule of customary international law, there are two facets that must be observed. Firstly, there must be evidence of State practice (usus) as well as  a belief that such practice is required, prohibited or allowed, depending on the nature of the rule, as a matter of law (opinio juris sive necessitatis).

Reverting to the opening statement relating to the VCLT, for a fact, less than half of the recognized States of the international community are actually parties to the treaty. Yet, the Courts have consistently considered its provisions as codifying customary law ((Anthony Aust, Modern Treaty Law and Practice (2nd edn. CUP, Cambridge 2007) 7–8 and n7))and have therefore treated them as being of general application to all states irrespective of their status in relation to the treaty. For instance, in the Kasikili/Sedudu Island Case the ICJ held that Article 31 of the VCLT relating to the interpretation of treaties reflected customary international law. Consequently, it was applicable to the case notwithstanding that neither Botswana nor Namibia was parties to the VCLT ((Case concerning Kasikili/Sedudu Island. (Botswana / Namibia). Judgment of 13 December 1999. para 18)).

For this reason, it is understandable that a fairly high threshold must be met when asserting that both elements are met and two cases from the ICJ in particular illustrates this proposition. On the hand the Case of the SS Lotus expressly showed that State practice in the absence of opinion juris will not suffice and the Advisory Opinion on Nuclear Weapons ((Legality of the Threat or Use of Nuclear Weapons, Advisory Opinion, I.C.J. Reports 1996, p. 226, International Court of Justice (ICJ), 8 July 1996, available at: [accessed 7 August 2013]))shows the converse to be true ((France. v. Turkey, 1927)). Despite the general acceptance of this definition however, it remains problematic when one considers that some international rules are permissive and reflect a belief in a right more so than an obligation. For this reason, the better view may be to consider opinion juris as an expression , assertion and acknowledgment of a legal right or obligation as opposed to a belief in one.

General Principles

It is submitted that in time, general principles of law may assume more importance than even international conventions and principles of customary law. The reason for this bold assertion is that in several areas, the law is being outstripped by technological developments. For instance, in the use of unmanned weapons or drones to combat acts of terrorism along a state’s border, the UN Charter and in particular Articles 2(4) and 51 may become problematic in their application.

On the one hand, the Charter outlaws the unlawful use of force, yet recognizes the inherent right of self-defence in respect of an armed attack. Where the latter is concerned, the there are certain procedures to be carried out before an act of self-defence is affected. The nature of unmanned weapons is such response to any such attack is immediate and would bring such a response outside the scope of the Charter. Yet, in the face of the 9/11 Terrorist Attack, is it reasonable to warrant that a State potentially compromise its security by following these procedures? Similarly, based on the principles enshrined in the Nicaragua Case it is doubtful whether the use of such technology fulfils the criteria laid out where anticipatory self defence is concerned. These questions are of course beyond the scope of this Article which merely aims to delineate the content of what are broadly considered sources of international law.  Nonetheless, to the extent that as Sir Gerald Fitzmaurice observed, a principle of law, as opposed to a rule, underlies a rule and explains the reasons for its existence. A rule answers the question ‘what’ whereas a principle answers the question ‘why ((Sir Gerald Fitzmaurice, ‘The General Principles of International Law’ (1957) 92 Collected Courses of the Hague Academy of International Law, p. 7.)), it is submitted that a principle may be more readily applied to emerging problematic areas of law, than a rule of for instance customary international law.

An apt example of the application general principles may be found in the Lena Goldfields Company Case where arbitrators recognized and indeed applied principles governing unjust enrichment as a general principle of law recognized by civilized nations ((H. C. Gutteridge, Transactions of the Grotius Society Vol. 38, Problems of Public and Private International Law, Transactions for the Year 1952 (1952), pp. 125-134- The Meaning and Scope of Article 38(1)(c) of the ICJ Statute)). In the landmark Chorzow Factory Case the Court categorically observed that, it is a principle of international law, and even a general conception of law, that any breach of an engagement involves an obligation to make reparation.  Whilst a comprehensive analysis of the precise scope and use of general principles supersedes the scope of the article, it may suffice to say that these principles essentially provide a mechanism to address international issues not already subject either to treaty provisions or to binding customary rules. Such general principles may arise both from municipal law and international law, and many may actually be described as procedural or evidential principles as well as those which affect with the machinery of the judicial process ((A; Bassiouni, M. Cherif, A Functional Approach to General Principles of  International Law,  Mich. J. Int’l L. 768 (1989-1990).)).

Judicial Decisions and Teachings of the Most Qualified Publicists

It is not surprising that the ICJ should recognize the utility of judicial decisions as a source of international law. In so far as there is no operation of binding precedent in international law, dissimilar to the operation of common law jurisdictions. Further, it is just as well that no distinction is made between judicial decisions of municipal and international courts. In relation to the latter, it is submitted that these too can be evidence of what is accepted as a general principle of law and even a customary practice.

In light of the growing problem of technology outstripping international customary principles and even broadly applicable treaties, the writings of qualified publicists are insightful on the dynamics that bring to bear on particular issues, and may also be reflective of the sentiment of that writer’s country on the issue. The benefits to an international tribunal are obvious, though such writings would never be seen as declaring the law. In view of the foregoing, an question which often emanates from these discussions is whether there is a hierarchy of sources of law.

A Hierarchy of Sources?

A simple answer to the question proposed would be in the negative. However such a sparse response would not adequately explain the matrices within which sources of law operate. To that end it is submitted that cognizance must be taken of rules of jus cogens which may be defined as customary international rules of the highest order. So much so, that Article 3 of the VCLT, 1969 explicitly states that even a treaty that seeks to enforce a practice contrary to such rules is void. Examples of such rules include the rule against torture, genocide and slavery.

However, if a rule of customary international law has not attained this status, nothing precludes States from contracting in a manner that contradicts such a customary rule. How the Court will deal with any dispute where treaty and custom conflict is another matter, but presumably the principle of pacta sunt servanda would prevail, particularly as a State may find itself bound by a customary practice that it arguably had no part in solidifying to the detriment of a treaty obligation. The latter, it is submitted is one of the ultimate expressions of State sovereignty, indeed at least theoretically, a State cannot be forced to subject itself to the terms of a treaty.  The extent to which a definitive hierarchy is even useful may be at best academic. Thus, it is respectfully submitted that for States, the best resolution in this case is not necessarily to try to find a hierarchy, but merely to attempt to discover the international rules and principles governing the legality or lack thereof of proposed state action coupled with an attempt to abide by them.