Interpretation of Treaties: Articles 31 to 33 of the VCLT

Most treaty disputes turn on what the treaty means. Articles 31 to 33 of the Vienna Convention set out a structured approach, starting with the text read in good faith, in context and in light of the treaty's object and purpose, and turning to the drafting history only as a supplementary aid. The ICJ treats these rules as customary law. This note explains the approaches, the three articles and the principles drawn from the cases.

1. Three Approaches

• Textual. The meaning lies in the words the parties chose, read in their ordinary sense.
• Intentions. The aim is to discover what the parties actually intended, using all available evidence, including drafting history.
• Teleological. The treaty should be read to achieve its object and purpose, an approach favoured for constituent instruments and human rights treaties.
• The Vienna synthesis. Article 31 starts from the text but requires it to be read in context and in light of object and purpose, so all three play a part, with the text given priority.

2. The Vienna Rules

Figure 1: Articles 31 to 33

• Article 31(1). A treaty shall be interpreted in good faith in accordance with the ordinary meaning to be given to its terms in their context and in the light of its object and purpose.
• Article 31(2): context. The text, including its preamble and annexes, and any agreement or instrument made in connection with the conclusion of the treaty and accepted by the parties.
• Article 31(3). There shall be taken into account, together with the context, (a) any subsequent agreement between the parties on interpretation or application, (b) any subsequent practice that establishes their agreement on interpretation, and (c) any relevant rules of international law applicable between the parties.
• Article 31(4). A special meaning is given to a term if it is established that the parties so intended.
• Article 32. Recourse may be had to supplementary means, including the preparatory work and the circumstances of conclusion, to confirm the meaning under Article 31, or to determine it when that meaning is ambiguous or obscure, or leads to a manifestly absurd or unreasonable result.
• Article 33. A treaty authenticated in two or more languages is equally authoritative in each; the terms are presumed to have the same meaning, and where a difference remains, the meaning that best reconciles the texts, having regard to object and purpose, is adopted.

3. Principles from the Cases

Figure 2: Leading decisions on interpretation

• Primacy of the text. In Competence of the General Assembly for the Admission of a State (1950), the Court held that if the words in their natural and ordinary meaning make sense in their context, that is the end of the matter; in Territorial Dispute (Libya/Chad), 1994, interpretation was said to be based above all on the text.
• Customary status. In Kasikili/Sedudu Island (Botswana/Namibia), 1999, the Court applied Articles 31 and 32 as customary law and examined subsequent practice.
• Effectiveness. A treaty should be read so that its provisions have effect rather than none (ut res magis valeat quam pereat), as applied in Corfu Channel (1949)
• Languages. In LaGrand (Germany v USA), 2001, the Court used Article 33 and the object and purpose of the Statute to hold that provisional measures under Article 41 are binding.
• Systemic integration. In Oil Platforms (Iran v USA), 2003, the Court read a treaty exception in light of the general law on the use of force under Article 31(3)(c)
• Evolutive interpretation. In Navigational and Related Rights (Costa Rica v Nicaragua), 2009, the generic term commerce in an 1858 treaty was read to include the carriage of tourists, its meaning evolving over time.
• Subsequent agreements and practice. The International Law Commission adopted conclusions on this subject in 2018.

4. Interpretation in Indian Courts

Although India is not a party to the Vienna Convention, Indian courts apply Article 31 as customary law. In AWAS Ireland (2015), the Delhi High Court applied the Article 31 rule of good faith, ordinary meaning, context and object and purpose to the Cape Town Convention. In G.M. Exports (2015), the Supreme Court held that a statute implementing a treaty should be read purposively and in conformity with the treaty (Topic 5).

5. Frequently Asked Questions

When can preparatory work be used to interpret a treaty?

Under Article 32, to confirm the meaning reached under Article 31, or to determine the meaning where Article 31 leaves it ambiguous or obscure or produces a manifestly absurd or unreasonable result.

Can the meaning of a treaty term change over time?

Yes, where the parties used a generic term intended to evolve. In Costa Rica v Nicaragua (2009), the ICJ read commerce in an 1858 treaty according to its present meaning, covering the carriage of tourists.

6. Related Topics

• Topic 13: Law of Treaties I. Conclusion and consent.
• Topic 14: Law of Treaties II. Reservations.
• Topic 16: Law of Treaties IV. Invalidity of treaties.