Ordinary meaning is the foundational rule of treaty interpretation codified in Article 31(1) of the Vienna Convention on the Law of Treaties (VCLT, 1969), which directs that a treaty be interpreted in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose.
In practice, interpreters begin with the natural, everyday sense of a word at the time the treaty was concluded, rather than a technical, legalistic, or party-specific reading. Ordinary meaning is not assessed in isolation: it is filtered through context (the full text, preamble, annexes, and related agreements under Article 31(2)) and the treaty's object and purpose. Where a term is ambiguous, obscure, or leads to a manifestly absurd result, interpreters may turn to supplementary means such as preparatory work (travaux préparatoires) under Article 32.
A term carries a special meaning only if it is established that the parties so intended (Article 31(4)) — for example, technical trade vocabulary in WTO agreements.
The approach has been applied extensively by the International Court of Justice, WTO Appellate Body, and investment tribunals. In US – Gasoline (1996), the WTO Appellate Body emphasized that interpretation must begin with the ordinary meaning of treaty language. In Competence of the General Assembly for the Admission of a State to the United Nations (ICJ, 1950), the Court stressed that if the natural and ordinary meaning is clear, no further interpretation is needed.
For diplomats and drafters, the doctrine has two practical consequences:
- Word choice matters. Negotiators should assume terms will be read in their plain sense by future tribunals.
- Dictionaries are evidence, not authority. They inform but do not determine ordinary meaning; context and purpose can override a dictionary definition.
Example
In the 1996 WTO US – Gasoline dispute, the Appellate Body interpreted GATT Article XX's chapeau by starting with the ordinary meaning of terms like 'arbitrary' and 'unjustifiable' discrimination.