When addressing context in treaty interpretation, the primary point of reference is the Vienna Convention on the Law of Treaties (the "Vienna Convention"). The Vienna Convention was adopted on 23 May 1969 by the United Nations.1 It entered into force for the original parties on 27 January 1980.2 The Vienna Convention constitutes one of the most important instruments of treaty law and is known as the "treaty on treaties".3 As of today, the Vienna Convention has been ratified by 116 States and signed by 45 others.4
When it comes to considerations of context in treaty interpretation, the obvious starting point is Article 31 of the Vienna Convention. Nevertheless, as paradoxical as it may seem, in the words of an author, this and other provisions of the Vienna Convention need "guidance" to be correctly applied as they are far from being straightforward.5
It is considered that some of the rules of the Vienna Convention constitute "a reflection of customary international law", and some non-ratifying States have even recognised this expressly.6 For instance, the rules of interpretation enshrined under Articles 31 to 33 of the Vienna Convention are considered as part of customary international law.7
Article 31 of the Vienna Convention, General Rule of Interpretation
1. A treaty shall 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.
2. The context for the purpose of the interpretation of a treaty shall comprise, in addition to the text, including its preamble and annexes:
(a) any agreement relating to the treaty which was made between all the parties in connection with the conclusion of the treaty;
(b) any instrument which was made by one or more parties in connection with the conclusion of the treaty and accepted by the other parties as an instrument related to the treaty.
3. There shall be taken into account, together with the context:
(a) any subsequent agreement between the parties regarding the interpretation of the treaty or the application of its provisions;
(b) any subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation;
(c) any relevant rules of international law applicable in the relations between the parties.
4. A special meaning shall be given to a term if it is established that the parties so intended.
Article 31 is called the "general rule", in opposition to the "supplementary means of interpretation" enclosed in Article 32 of the Vienna Convention. It is considered that a hierarchy exists between the two provisions: Article 31 takes precedence to preserve the plain language of the treaty, whereas Article 32 may be relied upon only in cases where Article 31 produces "ambiguous, obscure, manifestly absurd or unreasonable results".8
The "context" under Article 31 is, therefore, both related to (i) the text of the treaty, including its preamble and annexes (i.e., Sections 1 and 2) and to (ii) the identification in the Vienna Convention of other items listed in paragraphs (a) and (b) of Section 2 of Article 31. The Vienna Convention thus provides for the "material which is to be taken into account as forming context".9 Context under Article 31 must not be confused with "the circumstances of [...] conclusion" of the treaty under Article 32, which relates, for instance, to the "politico-economic background" of the conclusion of a treaty.10
The primary reason for looking to the context in treaty interpretation is to confirm the ordinary meaning given to the terms of the treaty or to identify such meaning in case of doubt.11
As the International Law Commission (ILC) affirmed in its commentaries on the Draft Articles of the Law of Treaties, "Once it is established – and on this point the Commission was unanimous – that the starting point of interpretation is the meaning of the text, logic indicates the 'ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose' should be the first element to be mentioned. Similarly, logic suggests that the elements comprised in the 'context' should be the next to be mentioned since they form part of or are intimately related to the text".12
The Context of the Treaty Stemming from Its Text – Terms of the Treaty in Their Context
The immediate context of the treaty comprises the grammatical construction or syntax of the provision within which a word that requires interpretation is located.13
Titles and headings may also serve as guidance for determining context in treaty interpretation. For example, in Plama v. Bulgaria, the tribunal analysed Article 17 (in Part III) of the Energy Charter Treaty, which is entitled "Non-Application of Part III in Certain Circumstances", and which reserves the parties' right to deny the advantages of this Part III (i.e., the substantive protection for investors under Part III) to any legal entity owned or controlled by nationals of a state not party to the ECT, if that entity has no substantial business activities in the state party in which it is set up. The tribunal relied on the heading of Part III to confirm its interpretation that denial of protection under Article 17 only excluded the rights of Part III but did not preclude it from exercising jurisdiction under Part V to determine whether, on the facts, Article 17 had been properly invoked (Bulgaria had raised a jurisdictional objection on the ground that Article 17 was applicable, i.e., no rights existed that could give rise to a claim under Part V).14
Another element that can be taken into account in order to determine context in treaty interpretation is the preamble of the treaty, which usually includes the aims, motivation and considerations in drawing up the treaty15 as it helps understanding and identifying the purpose and object of the treaty.16
Punctuation also plays a role in interpreting the terms of the treaty in their context.17
Finally, the link between the terms of the treaty in their context and the "object and purpose" of the treaty as provided under Article 31(1) of the Vienna Convention is illustrated in the Application of the Convention on the Prevention and Punishment of the Crime of Genocide where the ICJ held that "it would be contrary to the object of the provision [Article VI of the Genocide Convention] to interpret the notion of 'international penal tribunal' restrictively in order to exclude from it a court which, as in the case of the ICTY, was created pursuant to a United Nations Security Council resolution adopted under Chapter VII of the Charter."18 This was despite the fact that the Court did not link this approach to any particular provision in the general rule of interpretation; it simply read the provision in question in its context to take account of the provision's object and purpose.19
The Context of the Treaty Stemming from Additional Sources
Here, the context in treaty interpretation is to be found in the additional sources listed in Article 31(2), which come in addition to the treaty's text, preamble and annexes.
First, paragraph (a) mentions agreements relating to the treaty made between all the parties in connection with the conclusion of that treaty. This typically consists of diplomatic notes, for instance, exchanged in connection with the treaty.20
Then, paragraph (b) mentions instruments made by one or more parties in connection with the conclusion of the treaty and accepted by the other parties as instruments related to the treaty. This can be illustrated by the executive orders directing the transfer of Iranian assets issued by President Jimmy Carter when the Algiers Accords were signed on 19 January 1981, ending the Iran hostage crisis, which were entirely separate documents from the Accords and were accepted by Iran. They were later relied upon by the Tribunal dealing with the Iran-United States Claims in order to interpret the Accords.21
As the ILC emphasised in its commentary on the Draft Articles of the Law of Treaties, "The principle on which this provision [Article 31(2)] is based is that a unilateral document cannot be regarded as forming part of the 'context' within the meaning of Article 27 [actual Article 31] unless not only was it made in connection with the conclusion of the treaty but its relation to the treaty was accepted in the same manner by the other parties."
Moreover, according to Article 31(3), together with the context, the interpreter must consider:
(a) any subsequent agreement between the parties regarding the interpretation of the treaty or the application of its provisions;
(b) any subsequent practice in the application of the treaty which establishes the agreement of the parties regarding its interpretation;
(c) any relevant rules of international law applicable in the relations between the parties.
Supplementary Means of Interpretation
Article 32 of the Vienna Convention, Supplementary Means of Interpretation, provides:
Recourse may be had to supplementary means of interpretation, including the preparatory work of the treaty and the circumstances of its conclusion, in order to confirm the meaning resulting from the application of article 31, or to determine the meaning when the interpretation according to article 31:
(a) leaves the meaning ambiguous or obscure; or
(b) leads to a result which is manifestly absurd or unreasonable.
A number of tribunals have considered that Article 32 of the Vienna Convention permits recourse as a supplementary means of interpretation in addition to a treaty's "preparatory work" and the "circumstances of its conclusion", as indicated by the word "including", to other supplementary means of interpretation that may be applied to confirm the meaning resulting from the application of Article 31 of the Vienna Convention.22 These tribunals have held that "Article 38(1)(d) of the Statute of the International Court of Justice provides that judicial decisions and awards are applicable for the interpretation of public international law as 'subsidiary means'. Therefore, these legal materials can be considered as 'supplementary means of interpretation' in the sense of Article 32 VCLT."23
As mentioned above, these supplementary materials should, however, only serve a tribunal to confirm a prior meaning or to resolve an issue of interpretation stemming from Article 31.24
Context in treaty interpretation, therefore, covers a wide range of elements both internal to the treaty itself and external. Together, these components help to understand the provisions of the treaty.
Footnotes
1. E. Shirlow and K. Gore, Chapter 1: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 2.
2. Vienna Convention on the Law of the Treaties (Vienna Convention), 23 May 1969.
3. Vienna Convention, 23 May 1969.
4. United Nations Treaty Collection entry on Vienna Convention (last accessed 25 April 2024).
5. R. Gardiner, Treaty Interpretation (2nd edn., 2015), p. 7.
6. E. Shirlow and K. Gore, Chapter 1: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 17.
7. R. Gardiner, Treaty Interpretation (2nd edn., 2015), p. 163.
8. E. Shirlow and K. Gore, Chapter 6: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 118. This is based on the wording of Article 32 of the Vienna Convention, which reads as follows: "Recourse may be had to supplementary means of interpretation, including the preparatory work of the treaty and the circumstances of its conclusion, in order to confirm the meaning resulting from the application of article 31, or to determine the meaning when the interpretation according to article 31: (a) leaves the meaning ambiguous or obscure; or (b) leads to a result which is manifestly absurd or unreasonable."
9. R. Gardiner, Treaty Interpretation (2nd edn., 2015), p. 197.
10. R. Gardiner, Treaty Interpretation (2nd edn., 2015), p. 197.
11. R. Gardiner, Treaty Interpretation (2nd edn., 2015), p. 198.
12. International Law Commission, Draft Articles on the Law of Treaties (1966), Articles 27-28 (from which Vienna Convention Articles 31 and 32 developed virtually unchanged), Cmt. 9.
13. See, e.g., Land, Island and Maritime Frontier Dispute (El Salvador/Honduras: Nicaragua intervening) Judgement, 11 September 1992, ICJ Rep. 351, paras. 373-374, where the issue was whether the ICJ had the authority to delimit disputed maritime boundaries. The question on the wording was whether the phrase in the agreement between the disputing parties "determination of a legal situation" was equivalent to "delimitation". The ICJ decided that while the word "determine" in English (and "determinar" in Spanish) could potentially imply delimitation, it had to be understood in its specific context. In the case at hand, the object of the verb "determine" was not the maritime spaces themselves but rather their legal situation, particularly in comparison to other related agreements. Additionally, the decision highlighted that both parties in the dispute recognised that the dispute was about a matter of sovereignty rather than a delimitation one. Therefore, the ICJ concluded that interpreting "determine" to mean delimitation in this context would be inconsistent with the broader context of the treaty and the intentions of the parties involved.
14. Plama v. Bulgaria, ICSID Case No. ARB/03/24, Decision on Jurisdiction, 8 February 2005, para. 147.
15. E. Shirlow and K. Gore, Chapter 6: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 206.
16. E. Shirlow and K. Gore, Chapter 6: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 206.
17. E. Shirlow and K. Gore, Chapter 6: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 207.
18. Application of the Convention on the Prevention and Punishment of the Crime of Genocide (Bosnia and Herzegovina v Serbia and Montenegro) 26 February 2007, ICJ Rep. 43, paras. 160 and 445.
19. E. Shirlow and K. Gore, Chapter 6: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 210.
20. E. Shirlow and K. Gore, Chapter 6: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 116.
21. E. Shirlow and K. Gore, Chapter 6: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 116.
22. The Canadian Cattlemen for Fair Trade v. USA, Award on Jurisdiction, 28 January 2008, para. 50; Chevron Corporation (USA) and Texaco Petroleum Company (USA) v. Ecuador, PCA Case No. 34877, Interim Award, 1 December 2008, para. 121; Caratube International Oil Company LLP v. Kazakhstan, ICSID Case No. ARB/08/12, Decision on Provisional Measures, 31 July 2009, para. 71.
23. The Canadian Cattlemen for Fair Trade v. USA, Award on Jurisdiction, 28 January 2008, para. 50; Chevron Corporation (USA) and Texaco Petroleum Company (USA) v. Ecuador, PCA Case No. 34877, Interim Award, 1 December 2008, para. 121; Caratube International Oil Company LLP v. Kazakhstan, ICSID Case No. ARB/08/12, Decision on Provisional Measures, 31 July 2009, para. 71.
24. E. Shirlow and K. Gore, Chapter 6: An Introduction to the VCLT and Its Role in ISDS: Looking Back, Looking Forward, in E. Shirlow and K. Gore, The Vienna Convention on the Laws of Treaties in Investor State Disputes: Evolution and History (2022), p. 118.
The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.
We operate a free-to-view policy, asking only that you register in order to read all of our content. Please login or register to view the rest of this article.