Soft Law, Unilateral Acts and Estoppel in International Law

Not every obligation in international law comes from a treaty or custom. Declarations, guidelines and codes that are not binding still guide conduct and shape new rules; these are called soft law. A state may also bind itself by its own public statement, or be prevented from denying a position it has led others to rely on. This note covers soft law, unilateral acts, and estoppel and acquiescence.

1. Soft Law

Figure 1: Examples of soft law instruments

• Meaning. Instruments with normative content that are not legally binding in themselves, such as declarations, resolutions, guidelines, codes of conduct and memoranda; also vague or aspirational clauses within treaties.
• Precursor to treaties. The Universal Declaration of Human Rights, 1948 led to the two Covenants of 1966; the Declaration of Legal Principles Governing the Activities of States in the Exploration and Use of Outer Space (1963) preceded the Outer Space Treaty, 1967.
• Evidence of custom. Declarations adopted with wide support may show opinio juris: the Friendly Relations Declaration, 1970 (resolution 2625) is treated as reflecting customary law on the use of force and non-intervention (Nicaragua, 1986)
• Interpretation and flexibility. Soft law helps interpret treaties and allows states to cooperate where a binding treaty is not yet possible, as with the Stockholm (1972) and Rio (1992) Declarations on the environment.
• In India. Courts have drawn on soft law: the Rio principles in Vellore Citizens (1996) and the Yogyakarta Principles in NALSA (2014)
• Criticism. It blurs the line between law and non-law and may be cited selectively.

2. Unilateral Acts

• Kinds. Promise, recognition, protest, waiver or renunciation, and notification.
• Binding force. A public declaration made with the intention to be bound can create legal obligations without any acceptance or quid pro quo; the basis is good faith.
• Who can bind the state. Heads of state, heads of government and foreign ministers; other ministers within their fields of competence.
• ILC Guiding Principles, 2006. The International Law Commission adopted Guiding Principles applicable to unilateral declarations of states capable of creating legal obligations, drawing on these cases.

Figure 2: When a statement binds a state

• Legal Status of Eastern Greenland (Denmark v Norway), PCIJ, 1933. The Norwegian Foreign Minister Ihlen told the Danish minister orally that Norway would not make any difficulties over the settlement of the question; the reply bound Norway, and Denmark was held sovereign over the whole of Greenland.
• Nuclear Tests (Australia and New Zealand v France), 1974. Public statements by the French President and ministers that France would stop atmospheric nuclear tests, made with the intention to be bound and addressed to the world, created a legal obligation; the claims therefore no longer had any object.
• Frontier Dispute (Burkina Faso/Mali), 1986. Remarks by Mali's head of state in a press interview were not binding; where the parties could have made an agreement, an intent to be bound by a unilateral statement is not readily inferred.
• Armed Activities (DRC v Rwanda), 2006. A minister of justice may in some circumstances bind the state, but the statement relied on was too general to amount to a binding commitment.

3. Estoppel and Acquiescence

Figure 3: Estoppel and acquiescence

• Estoppel. A state that has made a clear and consistent representation, on which another state has relied in good faith to its detriment, cannot later take a contrary position; the elements were discussed in North Sea Continental Shelf (1969)
• Acquiescence. Tacit recognition shown by unilateral conduct, or by silence where a protest was called for, which the other party may treat as consent (Gulf of Maine, 1984)
• Temple of Preah Vihear (Cambodia v Thailand), 1962. Thailand had accepted and benefited from a map placing the temple in Cambodia for about fifty years, including during a 1930 visit by Prince Damrong; it was precluded from denying the map, and the temple was held to be in Cambodian territory.
• Arbitral Award of the King of Spain (Honduras v Nicaragua), 1960. Nicaragua, having by express declaration and conduct recognised the 1906 award as valid, could not later challenge it.

4. Frequently Asked Questions

Can an oral statement bind a state?

Yes. In Eastern Greenland (1933), an oral reply by Norway's Foreign Minister to the Danish minister was held binding on Norway. What matters is the intention to be bound and the authority of the person making the statement.

Is the Universal Declaration of Human Rights binding?

Not as a General Assembly resolution. Many of its provisions are, however, widely regarded as reflecting customary international law, and its content became binding treaty law through the 1966 Covenants.

What is the difference between estoppel and acquiescence?

Estoppel rests on a clear representation by one state and reliance on it by another. Acquiescence arises from silence or inaction where a protest would be expected, which is read as tacit consent. Both rest on good faith and often appear together, as in Preah Vihear (1962).

Does a unilateral declaration need to be accepted by other states?

No. In Nuclear Tests (1974), the ICJ held that a public declaration made with the intention to be bound creates a legal obligation without any acceptance, reply or reaction from other states, because good faith requires the declaring state to keep its word.

5. Related Topics

• Topic 9: General Principles, Judicial Decisions, Writers and Equity. Good faith and estoppel as principles.
• Topic 12: Codification. The International Law Commission.
• Topic 25: Acquisition and Loss of Territory. Acquiescence and title.