Treaties as a Source of International Law

Article 38(1)(a) of the Statute of the International Court of Justice identifies international conventions, whether general or particular, as a source of international law.

Treaties are particularly important because they allow States to expressly establish the rules to which they agree to be bound.

They perform two major functions:

Codification — recording and systematising rules that may already exist in customary international law.
Law-making — creating new legal obligations and standards for the parties.

Vienna Convention on the Law of Treaties, 1969

The Vienna Convention on the Law of Treaties provides the principal framework governing treaties between States.

It deals with matters including:

conclusion of treaties;
consent to be bound;
reservations;
entry into force;
interpretation;
amendment;
modification;
invalidity;
termination;
withdrawal;
suspension;
observance of treaties.

The Convention is therefore often described as the principal codification of the law of treaties.

Essential Elements of a Treaty

A treaty generally involves the following elements:

1. International Agreement

There must be an agreement between the parties.

2. Parties with Capacity

The parties must possess the necessary capacity under international law to conclude the agreement.

3. Intention to Create Legal Obligations

The agreement must be intended to create rights and obligations governed by international law.

4. Consent

The parties must consent to be bound in accordance with the applicable rules.

5. Regulation by International Law

The agreement must operate within the framework of international law.

Treaty-Making Process

Treaty-making generally involves several stages.

Negotiation

States negotiate the text and terms of the proposed treaty.

Negotiations may occur bilaterally or multilaterally.

Adoption of the Text

The negotiating States formally adopt the text of the treaty.

Authentication

The final text is authenticated as the agreed text.

Signature

States may sign the treaty.

Signature may have different legal effects depending upon the treaty and circumstances. In some cases, signature expresses consent to be bound; in others, the treaty requires a further step such as ratification.

Ratification

Ratification is the formal confirmation by a State of its consent to be bound by the treaty where the applicable treaty or constitutional process requires it.

Acceptance or Approval

Some States use acceptance or approval as alternative procedures for expressing consent to be bound.

Accession

A State that did not participate in the original conclusion of a treaty may become a party through accession where the treaty permits it or the existing parties otherwise agree.

Entry into Force

A treaty becomes legally operative according to the conditions specified in the treaty.

The entry-into-force provision may require a particular number of ratifications or other conditions.

Consent is central to treaty law.

Under the Vienna Convention, a State may express consent to be bound by methods including:

signature;
exchange of instruments constituting a treaty;
ratification;
acceptance;
approval;
accession;
another agreed method.

The applicable method depends upon the treaty and the circumstances.

Pacta Sunt Servanda

One of the most important principles of treaty law is pacta sunt servanda.

Article 26 of the Vienna Convention provides that every treaty in force is binding upon the parties and must be performed by them in good faith.

The principle means:

A State cannot simply disregard a treaty obligation after becoming legally bound by it.

Pacta sunt servanda provides stability and reliability to treaty relations.

Without it, international agreements would have little practical legal value.

Treaties and Good Faith

Good faith is fundamental to the operation of treaty law.

States are expected to:

perform their treaty obligations honestly;
interpret and apply treaties consistently with their obligations;
avoid deliberately frustrating the object and purpose of agreements;
comply with legally binding treaty commitments.

Good faith is therefore closely connected with pacta sunt servanda.

Treaties and Third States

A basic principle of treaty law is that a treaty does not ordinarily create obligations or rights for a third State without its consent.

This principle is reflected in Articles 34–38 of the Vienna Convention.

Pacta Tertiis

The principle is commonly expressed through the maxim:

pacta tertiis nec nocent nec prosunt

Broadly, agreements neither impose obligations upon nor confer rights upon third States without the required legal basis and consent.

However, the Vienna Convention recognises specific circumstances concerning rights or obligations of third States.

Reservations

A reservation is a unilateral statement made by a State when signing, ratifying, accepting, approving or acceding to a treaty, by which it purports to exclude or modify the legal effect of certain provisions of the treaty in their application to that State.

Reservations are particularly important in multilateral treaties.

They allow States to become parties while limiting the application of particular provisions, subject to the legal requirements governing reservations.

Limitations on Reservations

A reservation is generally impermissible where:

the treaty prohibits it;
the treaty permits only specified reservations and the proposed reservation falls outside them;
the reservation is incompatible with the object and purpose of the treaty.

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Interpretation of Treaties

Treaty interpretation is primarily governed by Articles 31–33 of the Vienna Convention.

General Rule

Article 31 requires a treaty to be interpreted:

in good faith;
according to the ordinary meaning of its terms;
in their context;
in light of the treaty’s object and purpose.

The context includes relevant elements identified by the Convention.

Supplementary Means

Article 32 permits recourse to supplementary means of interpretation, including:

preparatory work of the treaty;
circumstances of its conclusion.

These may be used to confirm the meaning resulting from Article 31 or to determine the meaning where interpretation under Article 31 leaves the meaning ambiguous or obscure or produces a manifestly absurd or unreasonable result.

Treaties Authenticated in Multiple Languages

Article 33 deals with treaties authenticated in two or more languages.

Where differences arise between authentic texts, interpretation must take into account the applicable rules of the Convention and the intention reflected in the treaty.

Amendment and Modification

Treaties may be amended or modified according to:

their own provisions;
agreement between the parties;
applicable rules of international law.

The Vienna Convention provides rules concerning both amendment and modification.

An amendment may change the treaty for the parties that accept the amendment, while modification may occur between some parties where the applicable conditions are satisfied.

Invalidity of Treaties

A treaty may be invalid in certain circumstances recognised by international law.

The Vienna Convention identifies grounds including:

error;
fraud;
corruption of a representative;
coercion of a representative;
coercion of a State by the threat or use of force;
conflict with a peremptory norm of general international law.

Jus Cogens

A treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general international law (jus cogens).

A treaty that conflicts with a newly emerging peremptory norm may also become void and terminate under the conditions recognised by the Convention.

Termination of Treaties

Treaties may terminate in several ways, depending upon the treaty and applicable law.

Possible grounds include:

termination according to the treaty’s provisions;
consent of the parties;
material breach;
impossibility of performance in recognised circumstances;
fundamental change of circumstances in limited situations;
emergence of a new peremptory norm;
other grounds recognised by the Vienna Convention.

Termination must therefore be distinguished from simply ceasing to perform an obligation.

Suspension of Treaties

A treaty may sometimes be suspended rather than terminated.

Suspension temporarily releases the parties from performing certain treaty obligations while the treaty remains legally in existence.

The grounds for suspension depend upon the treaty and applicable international law.

Material Breach

A material breach may provide grounds for terminating or suspending a treaty in circumstances recognised by the Vienna Convention.

A material breach includes:

repudiation of the treaty not sanctioned by the Convention; or
violation of a provision essential to the accomplishment of the treaty’s object or purpose.

The legal consequences depend upon whether the treaty is bilateral or multilateral and the circumstances of the breach.

Fundamental Change of Circumstances

The doctrine of rebus sic stantibus permits reliance upon a fundamental change of circumstances only in limited circumstances.

Under the Vienna Convention, the change must generally:

have been unforeseen;
constitute an essential basis of the parties’ consent;
radically transform the extent of obligations still to be performed.

The doctrine is applied restrictively because allowing States to escape treaty obligations too easily would undermine pacta sunt servanda.

Treaties and Customary International Law

Treaties and customary international law have an important relationship.

A treaty may:

codify an existing customary rule;
crystallise an emerging customary rule;
contribute to the development of a new customary rule;
create obligations binding specifically upon its parties.

Therefore, a treaty provision may have significance beyond the treaty itself if the rule also reflects or develops customary international law.

Treaties as Evidence of Custom

A treaty provision may provide evidence of customary international law.

However, the mere existence of a treaty provision does not automatically establish that the same rule is customary law.

The customary status of a rule must be assessed according to the requirements for customary international law, including relevant State practice and opinio juris.

Treaties and Non-Part States

A treaty generally binds its parties.

A State that is not a party is not ordinarily bound by the treaty simply because the treaty exists.

However, a treaty rule may also bind a non-party State if the same rule independently exists as customary international law or another applicable legal rule.

Classification of Treaties

Treaties may be classified in several ways.

Bilateral Treaties

Treaties concluded between two parties.

Examples include agreements concerning:

boundaries;
extradition;
trade;
cooperation.

Multilateral Treaties

Treaties involving several parties.

Examples include major international conventions concerning:

human rights;
environment;
international organisations;
diplomatic relations.

Law-Making Treaties

Treaties intended to establish general rules applicable among a significant group of States.

Treaty Contracts

Treaties primarily concerned with specific reciprocal arrangements between the parties.

Importance of Treaties

Treaties perform several important functions in international law.

1. Creating Legal Obligations

Treaties allow States to voluntarily establish binding legal commitments.

2. Codifying Existing Law

Treaties can codify rules that previously existed as customary international law.

3. Developing International Law

Treaties can create new legal standards and contribute to the development of customary rules.

4. Promoting Cooperation

Treaties establish frameworks for cooperation in areas such as:

trade;
environment;
health;
security;
human rights;
criminal justice.

5. Resolving Disputes

Treaties may establish:

dispute-settlement procedures;
arbitration mechanisms;
jurisdictional arrangements;
obligations to negotiate or mediate.

Important Cases

North Sea Continental Shelf Cases, 1969

The ICJ examined the relationship between treaty provisions and customary international law.

The Court considered whether the equidistance rule contained in the 1958 Geneva Convention on the Continental Shelf had become binding as customary international law.

The case is important for understanding how treaty provisions and customary rules may interact.

Reservations to the Convention on Genocide, 1951

The ICJ considered the permissibility of reservations to multilateral treaties.

The Court developed an important approach based on compatibility with the object and purpose of the treaty.

The advisory opinion had a major influence on the subsequent development of treaty law concerning reservations.

Gabčíkovo-Nagymaros Project, 1997

The ICJ examined treaty obligations, material breach, necessity and fundamental change of circumstances in the context of a major development project between Hungary and Slovakia.

The case demonstrates the importance of pacta sunt servanda and the restrictive approach to escaping treaty obligations.

Qatar v. Bahrain, 1994

The ICJ examined whether certain exchanges and instruments constituted binding international agreements.

The case is important for demonstrating that the legal character of an international agreement depends upon the intention and circumstances rather than simply its formal title.

Aegean Sea Continental Shelf, 1978

The ICJ considered whether instruments and declarations relied upon by the parties created a legal basis for the Court’s jurisdiction.

The case illustrates the importance of determining whether an international instrument creates binding legal obligations.

Important Distinctions

Treaty vs Customary International Law

Point	Treaty	Customary International Law
Formation	Express agreement	General State practice accepted as law
Consent	Usually explicit	May operate without a specific treaty commitment
Written form	Generally written	May be unwritten
Binding scope	Primarily parties	Generally broader where customary rule exists
Evidence	Treaty text	Practice and opinio juris

Signature vs Ratification

Point	Signature	Ratification
Meaning	Formal signing of treaty text	Formal confirmation of consent to be bound where required
Effect	Depends on treaty and circumstances	Establishes consent where ratification is the applicable method
Always required?	No	No
Relationship	May precede ratification	May follow signature

Termination vs Suspension

Point	Termination	Suspension
Effect	Treaty ceases to operate for the relevant parties	Operation is temporarily halted
Legal existence	Generally ends	Continues
Duration	Permanent unless treaty is later concluded anew	Temporary
Basis	Governed by applicable international law	Governed by applicable international law

Reservation vs Interpretation

Point	Reservation	Interpretation
Purpose	Exclude or modify legal effect of provisions for reserving State	Determine meaning of treaty provisions
Timing	Made in connection with expressing consent	Can arise whenever treaty meaning must be determined
Effect	May alter application of provisions to reserving State	Clarifies meaning of existing provisions

Common Confusions

Is every international agreement a treaty?

No.

An international instrument must satisfy the requirements for a treaty under applicable international law. Political declarations or other arrangements may not necessarily create binding treaty obligations.

Does signing always make a State legally bound by the whole treaty?

No.

The legal effect of signature depends upon the treaty and the circumstances. A State may need to ratify, accept or approve the treaty before becoming bound.

Can a State withdraw from any treaty whenever it wants?

No.

Withdrawal depends upon the treaty and applicable international law. If a treaty contains no withdrawal provision, the Vienna Convention provides restrictive rules governing whether withdrawal is possible.

Can a State ignore a treaty because its domestic law says otherwise?

Generally, no.

Article 27 of the Vienna Convention establishes that a party may not invoke its internal law as justification for failure to perform a treaty, subject to the specific rule concerning internal law and competence to conclude treaties.

Can a treaty bind a State that never became a party?

Not merely because the treaty exists.

A non-party State is generally not bound by the treaty itself. However, a treaty rule may independently apply to it if the rule also exists under customary international law or another applicable legal basis.

Can treaties override jus cogens?

No.

A treaty conflicting with a peremptory norm of general international law is void under the Vienna Convention.

Topic at a Glance

Point	Position
Source	Treaties / International Conventions
Principal provision	Article 38(1)(a), ICJ Statute
Principal treaty framework	Vienna Convention on the Law of Treaties, 1969
Core principle	Pacta sunt servanda
Key rule	Treaties in force are binding and must be performed in good faith
Formation	Negotiation, adoption, authentication, signature and consent to be bound
Consent	Signature, ratification, acceptance, approval, accession or agreed method
Reservations	Permitted subject to treaty and international law
Interpretation	Articles 31–33, Vienna Convention
Third States	Generally no obligations without consent
Invalidity	Includes coercion, fraud, error and conflict with jus cogens in specified circumstances
Termination	Governed by treaty and international law
Key cases	North Sea Continental Shelf, Genocide Reservations, Gabčíkovo-Nagymaros, Qatar v. Bahrain
Main importance	Creates, codifies and develops international legal obligations

Quick Revision

Treaties are one of the principal sources of Public International Law.
Article 38(1)(a) of the ICJ Statute recognises international conventions as a source of international law.
The Vienna Convention on the Law of Treaties, 1969 provides the principal framework governing treaties between States.
A treaty is an international agreement governed by international law.
The title of an instrument does not alone determine whether it is legally a treaty.
Treaties may be bilateral or multilateral.
The treaty-making process may involve:
- negotiation;
- adoption;
- authentication;
- signature;
- ratification;
- acceptance or approval;
- accession;
- entry into force.
Pacta sunt servanda is a fundamental principle of treaty law.
Article 26 VCLT requires treaties in force to be performed in good faith.
Article 27 VCLT generally prevents States from invoking internal law to justify failure to perform a treaty.
Reservations may be made subject to the treaty and applicable international law.
A reservation cannot be made where it is incompatible with the object and purpose of the treaty.
Articles 31–33 VCLT govern treaty interpretation.
Treaties generally do not create obligations for third States without their consent.
Treaties may codify existing customary international law.
Treaty provisions may also contribute to the development of customary international law.
Treaties may be invalidated in circumstances recognised by international law.
A treaty conflicting with jus cogens is void.
Treaties may be terminated or suspended according to applicable international law.
North Sea Continental Shelf is important for the relationship between treaties and custom.
Reservations to the Genocide Convention is important for treaty reservations.
Gabčíkovo-Nagymaros Project is important for treaty performance, breach and termination.
Treaties provide predictability, stability and structured cooperation in international relations.

Conclusion

Treaties are a fundamental source of international law because they provide States with a formal mechanism for creating binding legal obligations. The Vienna Convention on the Law of Treaties establishes the principal framework governing their formation, interpretation, performance, amendment, invalidity and termination. The principle of pacta sunt servanda ensures that treaties in force are performed in good faith, while rules concerning reservations, third States and treaty interpretation provide stability and predictability. Treaties also interact closely with customary international law: they may codify existing rules, crystallise emerging rules or contribute to the development of new customary norms. Consequently, treaties remain one of the most important instruments through which the international legal system creates and develops binding rules.

Author

Treaties as a Source of International Law

Meaning of a Treaty