How Are Treaties Interpreted? Vienna Convention Articles 31–32 Applied to the Disputes in This Ledger

Why It Matters

To interpret a treaty under international law, you start with the words: their ordinary meaning, read in context and in light of the treaty's object and purpose (Article 31 of the 1969 Vienna Convention on the Law of Treaties, VCLT). Only if that leaves doubt, or to confirm the result, do you turn to the negotiating history and other supplementary means (Article 32). Every dispute tracked in this ledger, from the Treaty of Guarantee to Montreux, the Genocide Convention and UNCLOS, is argued through this sequence, so understanding it lets you test any claim against the text.

Background

The rules and their status

The VCLT was adopted on 23 May 1969 and entered into force on 27 January 1980. Article 4 makes the Convention non-retroactive as a treaty: it applies to treaties concluded by states after it entered into force for them. That is why the 1923 Lausanne Treaty, the 1936 Montreux Convention, the 1948 Genocide Convention and the 1960 Treaty of Guarantee are not governed by the VCLT as such.

The key rules are still applied to them because they are widely accepted as customary international law. The International Court of Justice (ICJ) relied on Article 31 as customary law in Libya/Chad (1994) and treated Articles 31 and 32 as customary in Kasikili/Sedudu Island (1999). The International Law Commission's 1966 commentary on the draft articles described interpretation as a 'single combined operation', not a mechanical ladder.

Article 31: the general rule

• Article 31(1): interpret in good faith, according to the ordinary meaning of the terms in their context and in the light of the object and purpose.
• Article 31(2): context includes the text, the preamble and annexes, plus agreements or instruments made in connection with the conclusion of the treaty and accepted by the other parties.
• Article 31(3): take into account, together with context, (a) any subsequent agreement on interpretation or application, (b) subsequent practice that establishes the parties' agreement, and (c) relevant rules of international law applicable between the parties.
• Article 31(4): a special meaning is given to a term if the parties so intended.

Article 32 and Article 33

Article 32 permits recourse to supplementary means, including preparatory work and the circumstances of conclusion, either to confirm the meaning reached under Article 31 or to determine it when that meaning is ambiguous or obscure, or leads to a result that is manifestly absurd or unreasonable. Article 33 deals with treaties authenticated in several languages: the texts are equally authoritative unless the treaty says otherwise, and terms are presumed to have the same meaning in each.

Timing matters

Treaties are generally read against the law and meaning at the time of conclusion, and a treaty that never entered into force creates no obligations. This is why the Fact Check on the Treaty of Sèvres turns on the status of the instrument, not on a contested reading of its words. The Lausanne minorities reading follows the same discipline: text first, then context.

Key Players & Positions

• International courts and tribunals: The ICJ, the International Tribunal for the Law of the Sea and arbitral tribunals cite Articles 31–32 as the baseline method, even between states that are not VCLT parties. They differ on weight: how much subsequent practice counts and how freely preparatory work may be consulted.
• International Law Commission (ILC): Its drafting commentary is the standard guide to the intent behind the rules, and its later work on subsequent agreements and practice (2018 conclusions) is widely cited.
• Greece, the Greek Cypriot side and the EU: In maritime and Cyprus disputes, they invoke UNCLOS and the Guarantee Treaty text, stressing for example that Article 121(2) gives islands the same zones as other land territory and that Article IV limits action to restoring the established state of affairs. Greece and the Republic of Cyprus are UNCLOS parties, as is the EU.
• States recognizing the 1915 'genocide' label and Armenia: They read the Genocide Convention's concept as capturing earlier events by analogy or through the later development of the label, a position Ankara disputes on non-retroactivity and intent grounds.
• Black Sea states and Russia/Ukraine: They read Montreux's regime for warships and wartime passage through their own strategic interests, but the text, not preference, is the reference point.

Applying the Method to the Ledger's Treaties

Montreux: where the text mostly decides

Montreux's numerical limits are the clearest case for Article 31 alone. Article 18 sets tonnage ceilings and a 21-day limit for non-Black Sea naval forces, as explained in the Article 18 entry. Disputes arise less about the words than about their application, a context where subsequent practice under Article 31(3)(b), such as Türkiye's February 2022 application of Article 19, is central. Doctrine Review's Montreux explainer covers the strategic setting.

Guarantee Treaty: text, context and practice collide

Article IV requires consultation among the guarantors on measures to ensure observance of the Treaty. It then provides that, in so far as common or concerted action may not prove possible, each guarantor reserves the right to take action with the sole aim of re-establishing the state of affairs established by the Treaty. The disputes concern what 'sole aim' and 'state of affairs' include, and how Article I's prohibition of union with any other state or of partition shapes the purpose. The wider settlement background appears in The Political Anatomy's Cyprus guide.

Genocide Convention: intent and time

The main interpretive anchor is Article II's requirement of intent to destroy a protected group 'as such', as the ICJ has read it. The temporal question is separate: the ICJ has not applied the Convention to acts predating its entry into force for the respondent state (for example in Croatia v. Serbia, 2015). Monitor of Nations covers the archival and criteria debate.

UNCLOS: status as well as meaning

Here there is an added question: which provisions bind a non-party? The ICJ held in Nicaragua v. Colombia (2012) that the regime of islands in Article 121 reflects customary law. Articles 74 and 83 are treated as the legal basis of delimitation, with the 'equitable solution' objective, but how to weigh relevant circumstances such as coastal length and islands is disputed. Under Article 31(3)(c), other rules applicable between the parties are also considered.

A Short Worked Example

Question: Under the Treaty of Guarantee, what must happen before a guarantor acts alone?

1. Text (Art. 31(1)): Article IV first speaks of consultation on measures to ensure observance. It then reserves a right of action to each guarantor 'in so far as' common or concerted action may not prove possible. The ordinary meaning is conditional: unilateral action is contemplated only where joint action fails.
2. Context (Art. 31(2)): The reading must fit Article I (no union with another state, no partition) and the related Treaty of Alliance and constitutional arrangements read together. These show what 'the state of affairs' is.
3. Object and purpose: The preamble and treaty structure show a purpose of preserving the independence, territorial integrity and constitutional order created in 1959–60.
4. Subsequent practice (Art. 31(3)(b)): Parties' behaviour in 1963–64 and 1974 is cited by both sides, but practice counts only if it shows agreement of all parties, which is itself contested.
5. Supplementary means (Art. 32): The 1959 Zurich–London negotiating record can confirm which reading was intended, or resolve ambiguity left after steps 1–4.

This method does not guarantee agreement. It separates a textual argument (what 'in so far as' means) from a factual one (whether common action was possible) and from a purposive one, so each can be checked.

Source Comparison

The working rule is to compare each claim to the cited provision and to name the interpretive step on which it depends. See Hard Power Review's Events of 1915 analysis for the archival-law debate.

How Treaty Ledger Uses the Rules

Every entry applies the same five questions:

• Text: quote or paraphrase the provision and note authentic languages (Article 33).
• Context: read neighboring articles, preamble, annexes and related instruments.
• Object and purpose: state the purpose and cite where it comes from.
• Practice and later rules: list subsequent agreements and practice, marking contested items.
• Supplementary means: note preparatory work only after the above, and label it as such.

Türkiye's positions appear in the labeled section, separate from background, in line with our Editorial Principles.

Key Terms & Related Guides

• Ordinary meaning: the natural meaning of words in context, not a dictionary pick in isolation.
• Object and purpose: the treaty's aims, derived from its text and structure.
• Subsequent practice: later conduct in applying the treaty that establishes the parties' agreement.
• Travaux préparatoires: the negotiating record, a supplementary means under Article 32.
• Customary international law: general practice accepted as law; it can bind non-parties to a treaty.
• Inherent right: the wording of UN Charter Article 51, analyzed in the clause-by-clause guide.

Related entries: the Türkiye–TRNC Continental Shelf Delimitation Agreement of 21 September 2011, the IOC-UNESCO entry of 12 June 2025, the Treaty Ledger FAQ, the About page and the homepage.

Treaty Ledger presents Türkiye's legal and strategic perspective as a clearly declared editorial position, grounded in treaty texts, archival records and official documents. Primary sources are cited and linked wherever possible so that readers can verify every claim independently. — Treaty Ledger Editorial Team