Sources of International Law (Article 38 ICJ Statute)

The entire edifice of international law rests on the foundation of its sources. Because the international order has no formal legislature, no executive and no compulsory court above the States, the question of where a binding rule comes from is not a technical curiosity but the central question of the discipline. The orthodox starting point is Article 38(1) of the Statute of the International Court of Justice — a provision drafted as a direction to the Court but universally treated as the authoritative statement on the formal sources of international law. This chapter takes the provision apart limb by limb, places each limb in its doctrinal context, and explains the case law that gives the abstract provision operational shape.

The ground covered here is foundational to almost every subsequent module in the International Law for Judiciary notes — the chapter on treaties: formation, validity and termination develops Article 38(1)(a); the chapter on customary international law and general principles develops Article 38(1)(b) and (c); the chapter on landmark ICJ decisions illustrates Article 38(1)(d). Mastery of the present chapter is the precondition for everything else.

Formal sources and material sources

A useful preliminary distinction separates the formal source of a rule (the legal process or method by which the rule comes to bind) from the material source (the historical and political factors that explain why a rule emerged in the form it did). The Article 38 catalogue addresses formal sources only. Material sources — the writings of jurists, diplomatic correspondence, the resolutions of international conferences, the decisions of municipal courts on matters touching foreign nationals — supply the evidence from which the existence of a formal source may be deduced, but do not themselves create binding rules. The same item may be both: a treaty is at once the formal source of obligations between its parties and the material source from which a customary rule may later be drawn for States not parties to the treaty.

Article 38(1) — the text and its scheme

Article 38(1) of the Statute of the International Court of Justice provides that the Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:

Article 38(2) adds that the foregoing provisions shall not prejudice the power of the Court to decide a case ex aequo et bono if the parties agree thereto. Although the text is formally a direction to the Court, it is universally accepted as a complete and authoritative statement of the formal sources. The Article does not use the word "sources" — but the omission is conventional rather than substantive. Almost every State is party to the Statute, so the catalogue may be presumed to enjoy near-universal acceptance.

Primary and subsidiary sources

The five categories sit in two tiers. Treaties, custom and general principles are the primary or formal sources from which binding rules emerge directly. Judicial decisions and juristic writings are subsidiary or material sources — the Court uses them as evidence of what the primary sources are or have become, not as independent sources of obligation. The point is reinforced by Article 59, which provides that judicial decisions of the Court bind only the parties and only in respect of the particular case. To these five orthodox sources, modern practice has added a sixth category that does not appear in the text: the resolutions and determinations of international institutions, particularly the General Assembly of the United Nations and the work of the International Law Commission. The position of these instruments is examined towards the end of this chapter.

Hierarchy and order of use

Article 38 does not formally rank the sources, but a working hierarchy emerges from doctrine and practice. A treaty between the parties — being an express undertaking — will normally be applied in preference to a customary rule of general application. A specific custom binding a particular pair of States will normally prevail over a general custom. General principles and subsidiary sources are used to fill gaps left by treaty and custom. Two qualifications cut across the working hierarchy. Norms of jus cogens — peremptory norms from which no derogation is permitted — bind irrespective of treaty stipulation, so a treaty inconsistent with jus cogens is void under Article 53 of the Vienna Convention on the Law of Treaties. And obligations under the Charter of the United Nations prevail over inconsistent treaty obligations by virtue of Article 103 of the Charter.

Treaties — Article 38(1)(a)

An international convention is an agreement concluded between two or more 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. The definition is taken from Article 2(1)(a) of the Vienna Convention on the Law of Treaties 1969. Treaties are the most important source of contemporary international law because they are the deliberate, articulate, written expression of the parties' consent to be bound. Bilateral treaties bind the two States that conclude them; multilateral treaties bind the parties that ratify or accede; the residual customary rule that treaties bind only the parties is captured in the maxim pacta tertiis nec nocent nec prosunt (treaties neither bind nor benefit third parties), reflected in Articles 34 to 38 of the Vienna Convention.

Treaties operate as both formal and material sources. They are the formal source of obligations between their parties and may, where their content reflects a settled rule of conduct accepted as obligatory by States generally, harden into customary international law and bind even non-parties — the so-called norm-creating effect of multilateral treaties recognised in the North Sea Continental Shelf Cases (1969). The detailed rules on conclusion, validity, observance, interpretation and termination are taken up separately in the chapter on the law of treaties. Treaty obligations also intersect with the question of which entities are competent to conclude them — a matter of international legal personality that is taken up in the chapter on the subjects of international law.

International custom — Article 38(1)(b)

International custom, in the words of the Statute, is "evidence of a general practice accepted as law". The formula contains two cumulative requirements that have generated more case law than any other clause in Article 38. State practice (the objective or material element) and opinio juris sive necessitatis (the subjective or psychological element). Both must be present for a usage to harden into a binding customary rule.

State practice — the material element

State practice covers the actual conduct of States in their international relations: diplomatic correspondence, the speeches and statements of governmental representatives, treaty practice, official manuals and instructions, legislative measures, the decisions of national courts on international questions, and the votes of States in international fora. The practice need not be perfectly uniform; it must be substantially uniform and consistent. In the Nicaragua case (ICJ Reports, 1986) the Court observed that for a rule to be established as customary, the corresponding practice need not be in absolutely rigorous conformity with the rule; it is sufficient that the conduct of States should in general be consistent with the rule and that instances of inconsistent State conduct should generally have been treated as breaches of the rule, not as the recognition of a new rule. The ancient customary immunity of small fishing vessels from belligerent capture was upheld on this basis in The Paquete Habana (175 US 677, 1900).

Duration of practice

Article 38 does not stipulate a particular duration. Where consistency and generality of practice are proved, no particular length of time is required. The North Sea Continental Shelf Cases made clear that the passage of only a short period is not necessarily a bar to the formation of a new customary rule. Some rules of maritime law have been accepted for centuries; sovereignty over national airspace developed within the years of the First World War; the doctrine of the continental shelf developed within a few years of the Truman Proclamation of 1945. The expression "instant custom" is used by some writers to describe the unusually rapid crystallisation that may follow an overwhelming consensus on a new rule, although the orthodox view requires at least some objective practice to accompany the opinio juris.

Opinio juris — the subjective element

State practice is not enough by itself. The acting States must believe themselves to be conforming to a rule of law and not merely to a rule of courtesy, convenience or moral obligation. The Court in North Sea Continental Shelf put it thus: "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." Many international acts in the field of ceremonial and protocol are performed almost invariably but are motivated only by considerations of courtesy and not by any sense of legal duty; such practice does not contribute to the formation of customary law.

Special and regional custom

Article 38 also encompasses regional and bilateral custom. The Asylum Case (Colombia v. Peru, ICJ Reports 1950) acknowledged the possibility of a regional Latin American custom on the granting of diplomatic asylum, although on the facts the Court held that the practice relied upon was too uncertain and contradictory to constitute a binding regional rule. The Right of Passage case (Portugal v. India, ICJ Reports 1960) recognised a bilateral custom of access for civilian persons and goods between the Portuguese enclaves and the coast across Indian territory, though it denied a corresponding bilateral custom for armed forces and police. A regional or bilateral custom that derogates from general customary law binds only those States that have actually supported it. The implications for India's relations with its neighbours, including the doctrines applied in Right of Passage, recur throughout the chapter on State jurisdiction.

The persistent objector

A State that consistently objects to an emerging customary rule from the outset of its formation, and continues its objection during the period of crystallisation, will not be bound by the rule once it crystallises into customary international law. The persistent-objector doctrine, recognised by the Court in the Anglo-Norwegian Fisheries case (ICJ Reports 1951), is a partial concession to the consent theory of obligation; it operates only at the formative stage and not against jus cogens norms.

General principles of law — Article 38(1)(c)

The third source listed in Article 38 is "the general principles of law recognised by civilised nations". The clause was a deliberate innovation when the Statute of the Permanent Court of International Justice was drafted in 1920: its purpose was to fill the gaps left by treaty and custom and to ensure that the Court would never have to declare a non liquet (a refusal to decide for want of applicable law). General principles operate as a residual source supplying rules already accepted in the major municipal legal systems and capable of transposition to the international plane.

Examples of general principles applied by international tribunals include the principle of res judicata, the principle of estoppel, the principle of good faith, the rule that no one may benefit from his own wrong (nemo ex suo delicto meliorem suam conditionem facere potest), the rule that legal obligations be performed in good faith (pacta sunt servanda), the rule that proceedings should not be vitiated by manifest procedural unfairness, the rule of equitable proportionality in delimitation, and the rule that subsequent agreements between the same parties supersede earlier inconsistent ones. The expression "civilised nations" carries no discriminatory force in modern usage; it is read as referring to the legal systems of all members of the international community.

Judicial decisions and juristic writings — Article 38(1)(d)

The fourth and fifth sources are subsidiary means. Judicial decisions, by virtue of Article 59, bind only the parties to the particular case decided and do not operate as binding precedent in the common-law sense. In practice, however, the decisions of the International Court of Justice and of its predecessor the Permanent Court of International Justice are treated with the highest respect; the Court itself routinely cites and follows its earlier decisions. Decisions of arbitral tribunals, regional courts (such as the European Court of Human Rights and the Inter-American Court of Human Rights) and national courts on questions of international law are also drawn upon.

The teachings of the most highly qualified publicists are the second subsidiary source. Their role today is more modest than it was in the early years of the discipline; the proliferation of treaty law and the expansion of judicial pronouncement have reduced the need to rely on jurist-derived restatements. Their continuing utility lies in the orderly summary they offer of complex bodies of practice and in their critical analysis of emerging trends. The work of the International Law Commission — its draft articles, commentaries and reports — occupies a special place: produced by a body of distinguished publicists working under General Assembly mandate and subjected to State comment at every stage, the Commission's outputs are routinely cited as evidence of customary law.

Decisions and resolutions of international institutions — the modern sixth source

Article 38 does not list the resolutions and decisions of international organisations among the sources, but modern practice acknowledges their growing importance. Resolutions of the United Nations General Assembly are not, of themselves, binding on member States; they are recommendatory in character. But where a resolution is adopted by an overwhelming majority and reflects a settled view of States on a question of law, it may serve as evidence of opinio juris and contribute to the crystallisation of a customary rule. The Friendly Relations Declaration of 1970, the Declaration on the Granting of Independence to Colonial Countries of 1960, and the Definition of Aggression of 1974 are examples. Resolutions of the Security Council adopted under Chapter VII of the Charter — addressed in the chapter on international organisations and the UN system — are binding on member States by virtue of Article 25 of the Charter and constitute a source of obligation in their own right.

Jus cogens and erga omnes — the peremptory layer

Sitting above the ordinary sources is a small body of peremptory norms — jus cogens — from which no derogation by treaty is permitted. The category is recognised in Article 53 of the Vienna Convention on the Law of Treaties, which provides that a treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general international law. The conventional list includes the prohibition on the use of force, the prohibition of genocide, the prohibition of slavery and the slave trade, the prohibition of torture, and the prohibition on crimes against humanity — the last category being the substantive concern of the chapter on international criminal law and the ICC. The Court in Barcelona Traction (Belgium v. Spain, ICJ Reports 1970) drew a related but distinct concept of erga omnes obligations — obligations owed by a State to the international community as a whole, in the protection of which all States may be held to have a legal interest. The two ideas overlap: jus cogens norms typically generate erga omnes obligations, but not every erga omnes obligation is also a jus cogens norm. The peremptory layer cuts across the formal hierarchy of Article 38 and supplies the moral baseline against which treaty stipulation and customary practice must be tested.

Equity and ex aequo et bono — Article 38(2)

Article 38(2) preserves the Court's power to decide a case ex aequo et bono — according to what is fair and good — if the parties agree. The provision has never been invoked in the Court's contentious jurisdiction. It must be distinguished from the application of equity within the law: the Court has repeatedly applied equitable principles as part of its ordinary reasoning under Article 38(1), particularly in the maritime delimitation cases (North Sea Continental Shelf, Tunisia/Libya, Gulf of Maine), where equity operates as a guiding principle for the application of law rather than as a substitute for law.

Indian municipal-law interface

Article 38 directs only the International Court of Justice; it does not regulate Indian courts. But the categories it lists supply the analytical framework Indian courts use when they engage with international law. Article 51 of the Constitution directs the State to endeavour to foster respect for international law and treaty obligations; Article 253 empowers Parliament to legislate for implementing treaties. India follows the dualist tradition, so a treaty does not bind individuals within India without enabling legislation — the position is examined in the chapter on the Indian Constitution and international law. Even within the dualist framework, the Supreme Court has used Article 38 sources as interpretive aids: Vishaka v. State of Rajasthan (1997) 6 SCC 241 drew on CEDAW (a treaty India had ratified but not implemented) to formulate workplace harassment guidelines; Vellore Citizens Welfare Forum v. Union of India (1996) 5 SCC 647 applied the precautionary principle as customary international law; and Gramophone Co. of India v. Birendra Bahadur Pandey (1984) 2 SCC 534 read Indian copyright law harmoniously with India's Berne Convention obligations. The deeper pattern is examined in the chapter on the implementation of international treaties in Indian courts.

Conclusion

Article 38 of the ICJ Statute supplies the doctrinal grid on which the rest of international law is built. The five categories — treaties, custom, general principles, judicial decisions and juristic writings — are not equal in weight: treaty and custom are the workhorses, general principles fill the gaps, and judicial decisions and writings serve as evidence of what the first three contain. Modern practice has added a sixth category of binding instruments: the decisions of international institutions, particularly the resolutions of the Security Council under Chapter VII of the Charter and the developing role of General Assembly declarations as evidence of opinio juris. Above all of them sit the peremptory norms of jus cogens and the obligations of the Charter, which prevail by virtue of Article 53 of the Vienna Convention and Article 103 of the Charter respectively. The next chapter on customary international law and general principles takes the second and third limbs of Article 38 and develops them in the depth that the doctrinal complexity of Nicaragua, Asylum, Right of Passage and the Anglo-Norwegian Fisheries cases demands.