Introduction — Definition, Nature and Basis of International Law

International law is the body of rules and principles which the international community recognises as binding upon its members in their mutual relations. The expression itself was coined by Jeremy Bentham in 1780 to displace the older phrase "law of nations". Today the discipline regulates not only the conduct of sovereign States towards one another but also a growing list of non-State actors — international organisations, individuals, and certain non-State entities — whose activities transcend national frontiers. The starting question for any student of the subject is foundational and deceptively simple: what is international law, and is it really law at all?

The chapter that follows answers three connected questions. First, how the discipline is defined — the journey from Oppenheim's classical formulation to the modern conceptions of Starke, Fenwick and Schwarzenberger. Second, what its nature is — the celebrated debate, opened by Austin and Holland, on whether a horizontal system without a world legislature, executive or compulsory court can be called "law" at all. Third, what its basis is — the jurisprudential explanation for why sovereign States, owing obedience to no superior, nonetheless treat international rules as obligatory. The answers form the doctrinal foundation on which the rest of the International Law for Judiciary notes are built.

Defining international law

There is no single universally accepted definition. The classical formulations were State-centric and rule-centric; modern formulations are pluralist and process-oriented. The shift mirrors the structural transformation of the international legal order after 1945.

The Oppenheim definition (1905) and its limits

The classical definition was given by Oppenheim in 1905: "Law of Nations or international law is the name for the body of customary and conventional rules which are considered legally binding by civilised States in their intercourse with each other." The definition served the inter-State system of its day but has since become obsolete on five separate counts. It is over-narrow on subjects — it treats only States as bearers of international rights and duties, ignoring the legal personality acquired since 1945 by international organisations and, to a limited extent, by individuals. It is over-narrow on sources — it limits international law to custom and treaty, omitting the "general principles of law recognised by civilised nations" recognised in Article 38 of the Statute of the International Court of Justice and explored in the chapter on sources of international law. It uses the discriminatory expression "civilised States", a phrase the Western powers historically used to exclude non-Christian polities; the term was deleted in later editions. It treats the rules as a static "body" though international law is in fact a continuously evolving process. And by saying that the rules are "considered" legally binding, it weakens the assertion of obligation that the discipline now firmly makes.

The 1992 Oppenheim revision and modern definitions

The ninth edition of Oppenheim, edited by Jennings and Watts in 1992, recast the definition: international law is "the body of rules which are legally binding on States in their intercourse with each other. These rules are primarily those which govern the relations of States, but States are not the only subjects of international law. International organisations and, to some extent, also individuals may be subjects of rights conferred and duties imposed by international law." This is broadly the modern position and is examined more fully in the chapter on the subjects of international law.

Other modern formulations cluster around the same theme. Fenwick describes international law as "the body of general principles and specific rules which are binding upon the members of the international community in their mutual relations" — the phrase "members of the international community" deliberately captures States, organisations, individuals and non-State entities together. Starke offers the most comprehensive formulation: international law is the body of law composed mainly of the principles and rules of conduct which States feel themselves bound to observe in their relations with each other, and which includes additionally the rules relating to the functioning of international organisations and certain rules relating to individuals and non-State entities so far as their rights and duties are the concern of the international community. Whiteman's compressed formulation — "international law is the standard of conduct, at a given time, for States and other entities subject thereto" — captures the same idea in a single sentence. Schwarzenberger refrains from naming the entities and defines international law as "the body of legal rules which apply between sovereign States and such other entities as have been granted international personality", leaving the membership of the international legal community open to expansion.

A working modern definition

Drawing the strands together, international law may be defined as a constantly evolving body of norms which the members of the international community commonly observe in their mutual relations, conferring rights and imposing obligations primarily upon States and to a lesser extent upon international organisations, individuals and non-State entities. The classical view captures the law's structural truth that States remain the primary law-makers and law-takers; the modern view captures its expanding scope. Lord Sankey's description in In re Piracy Jure Gentium (1934 AC 586) of international law as a "living and expanding code" remains a serviceable epigraph.

Distinguishing related expressions

Three terminological distinctions clear the ground. First, "international law" is used in this chapter as identical with public international law and is to be sharply contrasted with private international law or conflict of laws — the body of rules within the municipal law of each State that determines which national law applies when a dispute carries a foreign element. The distinction is developed in the chapter on public vs private international law. Second, international law must be distinguished from international comity — practices observed between States as a matter of courtesy or convenience (the salute of foreign warships, the visa-free entry between Canada and the United States, the open-border arrangement between India and Nepal). Comity carries no legal obligation and breach of it is not an internationally wrongful act. Third, international law must be distinguished from international morality — the standard of right behaviour based on personal or collective judgement. Moral arguments may inform international claims but, when States actually contest a question of international law, they appeal to precedents, treaties and the writings of specialists, not to general feelings of moral rightness.

Is international law really law? The Austinian challenge

The most enduring debate in the discipline concerns its very legal character. The challenge is associated with John Austin and Sir Thomas Erskine Holland; the modern reply with Oppenheim, Hart, Starke and Brierly. The conventional Indian position, attributed to Paton and Starke, is that international law is law in the true sense, but a weak law. The whole controversy turns on the definition of "law" itself.

Austin's positivism — international law as positive morality

Austin defined law as "a command of the sovereign attended by sanction in case of violation of the command". Law on this analysis must be (a) a command (b) issued by a determinate political superior (c) enforced by physical sanction. Applying this test, Austin concluded that international law fails on every limb. There is no world sovereign issuing commands; there is no world legislature; there is no world police force capable of enforcing rules against a recalcitrant State; and the rules at the time he wrote were almost entirely customary, not enacted. What is conventionally called international law is therefore a body of "positive international morality" — rules analogous to the rules of an unincorporated club, observed by States out of fear of provoking general hostility but not legally binding. Lord Coleridge CJ adopted exactly this view in Queen v. Keyn (1876) 2 Ex D 63, observing that "law implies a law-giver, and a tribunal capable of enforcing it and coercing its transgressors".

Holland — the vanishing point of jurisprudence

Holland reached the same conclusion by a different route. International law, he said, is the "vanishing point of jurisprudence" because there is neither a sovereign authority to make it nor any sanction beyond public opinion to enforce it. Without a judge or arbiter standing above the disputing States, law in the strict sense is a contradiction in terms. International law is therefore "law by analogy" only — practices voluntarily, though habitually, observed by States in their dealings with one another, resting on consent and courtesy rather than command and sanction.

The modern reply

Six lines of criticism have largely overtaken the Austinian view. First, Austin's definition is itself too narrow. Many primitive communities have effective legal systems operating through customary rules without a determinate sovereign legislator; English common law itself grew out of judicial decisions on customary practice. To exclude custom from the category of law is to disqualify large parts of the legal experience of mankind. Second, the premise that there is no international legislative process no longer holds. The modern law of treaties — codified in the Vienna Convention and explored in the chapter on treaties: formation, validity and termination — supplies a settled procedure for the formulation of binding rules through multilateral conventions and the work of bodies such as the International Law Commission. Third, the premise that there is no international judiciary ignores the International Court of Justice, whose judgments are binding on parties and whose enforcement may, under Article 94 of the UN Charter, be referred to the Security Council. The detailed position is examined in the chapter on the settlement of international disputes and again in the survey of landmark ICJ decisions involving India. Fourth, the premise that there is no sanction mistakes the texture of international enforcement: collective measures under Chapter VII of the Charter, reciprocal countermeasures, reputational cost and the diplomatic isolation of a law-breaker all operate as sanctions, even if they are not centrally administered like a domestic police force. Fifth, States themselves treat the rules as binding — they justify their conduct by reference to international law rather than by denying its existence, a fact Hart captured in his deceptively simple formulation that "international law is law because States regard it as law". Sixth, the empirical record cuts against the Austinian view: as Henkin's celebrated aphorism puts it, "almost all nations observe almost all principles of international law and almost all of their obligations almost all of the time".

The settled position — true law, but a weak law

The position now generally accepted is that international law is true law but, by comparison with developed municipal legal systems, a weak law. The weaknesses are structural rather than conceptual. The legislative machinery operates through treaties and consensus at international conferences, which is slower and more uncertain than parliamentary legislation. The executive machinery — chiefly the Security Council — is paralysed by the veto power of its five permanent members and is in any event incapable of immediate enforcement. The judicial machinery is non-compulsory: the ICJ may exercise contentious jurisdiction only with the consent of the parties, and even where jurisdiction exists, enforcement of judgments depends on the political will of the Security Council. Sanctions are precarious and asymmetrically applied, working better against weak States than against the powerful. And in matters within the "domestic jurisdiction" of a State the law's reach is severely curtailed. Yet none of these weaknesses negates the legal character of the rules themselves. As Brierly observed, the existence of some kind of international law is the inevitable consequence of the co-existence in the world of a plurality of States necessarily brought into relations with one another.

Basis of obligation — why international law binds

If international law is law, what makes it binding on sovereign States who acknowledge no superior? The question is jurisprudential rather than political and has produced three principal schools of answer: naturalism, positivism, and the eclectic or Grotian compromise.

Naturalist theory — the law of reason

The naturalist school, dominant in the seventeenth and eighteenth centuries and associated with Pufendorf, locates the binding force of international law in a higher "law of nature" — a system of universal principles emanating from human reason and the rational nature of man. International law on this view is part of natural law and binds States because, as members of the universal moral community, they are obliged to observe the rules necessary for the peaceful maintenance of that community. Hart's modern restatement put it on a minimum-content basis: the rules necessary for the survival of mankind are inherent in human nature, recognised by reason and confirmed by experience. International peace and security being necessary for survival, the rules relating to them are part of the law of nature. The naturalist account explains the binding force of jus cogens norms (peremptory rules from which no derogation is permitted), the principle of pacta sunt servanda (treaties must be observed), and the contemporary movement to protect international human rights. Its weakness — that "natural law" is too vague and too disconnected from State practice to ground specific rules — is real but not fatal: the naturalist tradition supplied much of the moral framework on which the modern positive law was later built.

Positivism — the consent of States

Positivism, dominant from the nineteenth century onwards and associated with Bynkershoek and Oppenheim, locates the binding force of international law in the will of the State. Two variants matter. The doctrine of the will of the State holds that international law is law because it has, in fact, been enacted or followed by States; in Triepel's formulation, the common will of States meeting in a law-making treaty produces the binding rule. The doctrine of consent, more influential in practice, holds that the rules become positive law when the State has consented to be bound — expressly through a treaty or impliedly through acquiescence in a customary rule. The Permanent Court of International Justice gave the doctrine its classical statement in the Lotus case: "The rules of law binding upon States... emanate from their own free will." The doctrine has obvious appeal: it explains why a State is bound by a treaty it has ratified and, with some strain, why it is bound by a custom it has helped to form.

Limits of pure consent and the modern compromise

Pure consent theory, however, fails at several points. It cannot adequately explain why a new State entering the community is automatically bound by pre-existing customary rules to whose formation it did not contribute. It cannot explain the binding force of jus cogens norms, which bind even against contrary consent. It cannot explain why the obligation should not lapse the moment consent is withdrawn — a result no working legal system could tolerate. And it cannot explain the binding character of general principles of law recognised by civilised nations and of judicial decisions, both of which appear in Article 38 of the ICJ Statute as sources independent of express consent. The modern position, reflected in the eclectic or Grotian school, harmonises the two traditions: naturalism supplies the moral foundation and the peremptory norms; positivism supplies the operational rules adopted through treaty and custom; and the binding force of the system as a whole rests on the compromised and coordinated wills of States, supplemented by considerations of legal conscience, opinio juris, reciprocity, self-interest and the necessity of co-existence in a globalised world.

The Indian municipal-law interface

India's relationship with international law is set by the Constitution. Article 51 directs the State to endeavour to foster respect for international law and treaty obligations in the dealings of organised peoples with one another — a Directive Principle, non-justiciable but constitutionally significant. Article 253 empowers Parliament to make any law for the whole or any part of the territory of India for implementing any treaty, agreement or convention with another country. India follows the dualist tradition: a treaty does not, of its own force, bind individuals within India; legislation is required to translate the treaty obligation into enforceable municipal law. The deeper account of this relationship is taken up in the chapter on the Indian Constitution and international law and in the chapter on the implementation of international treaties in Indian courts. Even within the dualist framework, the Supreme Court has repeatedly used international instruments as interpretive aids — in Vishaka v. State of Rajasthan (1997) 6 SCC 241 the Court drew directly on CEDAW to lay down workplace harassment guidelines, and in Gramophone Co. of India v. Birendra Bahadur Pandey (1984) 2 SCC 534 it held that comity of nations may require domestic courts to read municipal statutes harmoniously with international obligations wherever the language permits.

Codification and the International Law Commission

Codification — the systematic reduction of customary and conventional rules into authoritative written form — has been a defining project of the modern era. The idea was sketched by Bentham at the close of the eighteenth century but found institutional expression only with the establishment of the International Law Commission by the United Nations General Assembly in 1947 under Article 13(1)(a) of the Charter. The Commission's mandate, set by Article 1 of its Statute, is the promotion of the progressive development of international law and its codification. Its 34 members, elected by the General Assembly on the nomination of member States, possess recognised competence in international law and reflect a broad spectrum of legal systems. The Commission has produced or laid the groundwork for landmark instruments — the four Geneva Conventions on the Law of the Sea (1958), the Vienna Convention on Diplomatic Relations (1961), the Vienna Convention on Consular Relations (1963), the Vienna Convention on the Law of Treaties (1969), the United Nations Convention on the Law of the Sea (1982) and the Draft Articles on the Responsibility of States for Internationally Wrongful Acts (2001). Its work on diplomatic and consular immunity is taken up in the chapter on diplomatic and consular privileges and immunities. Codification has its critics — it risks freezing a still-developing system, encourages hair-splitting interpretation, and is necessarily partial because customary rules continue to outpace written ones — but the advantages of accessibility, certainty and intelligibility are now generally regarded as outweighing the costs.

Conclusion — a living and expanding code

The introduction to international law leaves the student with three settled propositions. International law is best defined as a constantly evolving body of norms that the members of the international community observe in their mutual relations, conferring rights and imposing obligations primarily upon States and increasingly upon international organisations and individuals. International law is law in the true sense — the Austinian denial, plausible in the nineteenth century when there was neither a world legislature nor a world court nor a sanctioning system, no longer holds against a discipline that today operates through codified treaties, an established Court at The Hague, an institutional framework of sanctions and a near-universal practice of States justifying their conduct by reference to legal rules. And the basis of its binding force lies neither in pure natural law nor in pure consent but in the compromised wills of States operating within a moral framework that has gathered force since 1945. The remaining chapters of these notes apply this foundation to the operative law: the sources, the subjects, the rules of State jurisdiction and diplomatic immunity, the regime of treaties, the protection of human rights, and the institutional architecture of the United Nations system. The departure point for all of them is the proposition that international law is, in Lord Sankey's phrase, a living and expanding code.

Frequently asked questions

Who first used the expression "international law" and when?

The English jurist Jeremy Bentham used the expression "international law" for the first time in 1780. He coined it to displace the older Latin-derived expression "law of nations" (jus gentium), which he considered ambiguous because it failed to distinguish between rules governing the conduct of States towards one another and rules governing the legal status of individuals across jurisdictions. Bentham's coinage stuck and is now the standard English-language label for the discipline. The expression "law of nations" is still occasionally used as a synonym, particularly in older texts and in continental European literature.

Why is the Oppenheim 1905 definition of international law considered obsolete?

Oppenheim's 1905 definition restricted international law to customary and conventional rules binding upon "civilised States" in their intercourse with one another. It is considered obsolete on five grounds. It limits the subjects of international law to States, ignoring international organisations and individuals; it limits the sources to custom and treaty, omitting general principles of law and judicial decisions recognised in Article 38 of the ICJ Statute; it uses the discriminatory expression "civilised States"; it treats the rules as a static body when international law is a dynamic and evolving system; and the qualifying phrase "considered legally binding" weakens the assertion of obligation. The 1992 ninth edition revised the definition to address these concerns.

Is international law a true law or only positive morality?

International law is true law, not merely positive morality. Austin's classical view — that law must be the command of a sovereign backed by sanction, and that international law fails this test — has been rejected on six grounds. The definition is too narrow because it excludes customary rules that operate as law in many primitive communities and in the common law itself. International legislative procedure now operates through multilateral treaties and the International Law Commission. The International Court of Justice supplies a judicial mechanism. Sanctions exist through countermeasures, Security Council action and reputational cost. States consistently treat the rules as binding. And as Henkin observed, almost all nations observe almost all of their international obligations almost all of the time.

Why is international law described as a "weak law"?

International law is true law but weak by comparison with developed municipal systems. The legislative machinery operates through treaties and consensus, which is slower and more uncertain than parliamentary legislation. The executive machinery is dominated by the Security Council, paralysed by the veto power of its five permanent members. The judicial machinery is non-compulsory: the International Court of Justice exercises contentious jurisdiction only with party consent, and enforcement of its judgments depends on the political will of the Security Council. Sanctions are precarious and asymmetric, working better against weaker States. And matters within the domestic jurisdiction of States are largely insulated from international scrutiny. These are structural weaknesses of the horizontal international order, not reasons to deny that the rules are law.

What is the difference between international law and international comity?

International law consists of rules that States are legally bound to observe in their mutual relations; breach attracts international responsibility. International comity consists of practices observed between States as a matter of courtesy, convenience or reciprocal goodwill; breach attracts no legal consequence. Examples of comity include the salute to foreign warships at sea, visa-free entry between Canada and the United States, and the open-border arrangement between India and Nepal. The treatment of diplomatic agents, by contrast, is governed by international law — specifically the Vienna Convention on Diplomatic Relations 1961 — and breach attracts the full range of legal consequences, including expulsion of the host State's diplomats and possible reference to the International Court of Justice.

How does India relate to international law within its constitutional framework?

India follows the dualist tradition: a treaty does not, by its own force, become part of municipal law or bind individuals within India. Article 51 of the Constitution directs the State to endeavour to foster respect for international law and treaty obligations — a non-justiciable Directive Principle of constitutional significance. Article 253 empowers Parliament to make law for implementing any treaty, agreement or convention with another country. The Supreme Court has, however, used international instruments as interpretive aids even without enabling legislation. In Vishaka v. State of Rajasthan (1997), the Court drew on CEDAW to frame guidelines on workplace sexual harassment; in Gramophone Co. of India v. Birendra Bahadur Pandey (1984), it held that comity may require municipal statutes to be read harmoniously with international obligations.