Why the VCLT Does Not Save Understanding Seven
Both Marko and Joanna Harrington (in comments) have relied on Article 31 of the Vienna Convention on the Law of Treaties to justify the idea that the Court will have to rely on understanding seven to interpret new Article 8bis, the idea being that the adoption of the understandings by consensus is a subsequent agreement that Article 31 makes relevant to the Rome Statute’s context. That argument, however, is inconsistent with the plain language of Article 31:
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: any agreement relating to the treaty which was made between all the parties in connection with the conclusion of the treaty; 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: any subsequent agreement between the parties regarding the interpretation of the treaty or the application of its provisions.
Notice the highlighted language — a subsequent agreement is binding under Article 31 only if all of the parties to a treaty accept that agreement. That’s an obvious requirement; a subset of the parties to a multilateral treaty cannot decide to change the terms of the treaty without the others’ consent. But it’s a requirement that is fatal to understanding seven, because there were at most 80 of the 111 States Parties present when the understandings were adopted by consensus. Nearly 30% of the parties to the Rome Statute have thus not accepted the understandings — which means that understanding seven cannot be binding under Article 31.
There is, of course, one exception to the rule that a subset of the parties to a multilateral treaty cannot change its terms without the consent of all of the other parties — namely, where the treaty itself provides for such non-unanimous changes. That is exactly what Article 121(3) of the Rome Statute does with regard to amendments:
The adoption of an amendment at a meeting of the Assembly of States Parties or at a Review Conference on which consensus cannot be reached shall require a two-thirds majority of States Parties.
There is a strong argument that Article 121(3) is poorly drafted — read literally, it would allow 10 States Parties to adopt an amendment on behalf of all 111 if only 10 were present at a particular moment during an ASP meeting or at a Review Conference. But at least Article 121(3) is in the Rome Statute. Nothing in Article 121 provides that a subset of the ASP can adopt an understanding by consensus. So, again, understanding seven can be binding on the Court only if qualifies as a subsequent agreement under Article 31 of the VCLT — and given that it was adopted by less than 75% of the States Parties, it obviously does not.