[Christian J. Tams holds the Chair of International Law at the University of Glasgow - School of Law]
Let me start off by saying that to participate in the Oxford Guide to Treaties has been a real privilege: it is a great book that combines theoretical reflection and practical insights. I am particular impressed by the list of treaty clauses included as Part VI. Unlike many other areas of international law, treaty law is a framework to give effect to the expressed will of parties. Of course, there are limits to what parties can agree to – jus cogens being the most important –, but they hardly ever act as real constraints on treaty-making. So any analysis of treaty law has to come to terms with the diversity of treaty practice. And as patterns of practice change over time, the topic itself is not static, but in a state of constant reform. That makes it so interesting.
At the same time, there is a risk – and it is reflected in Duncan’s post, even though I would describe it slightly differently. In many respects, the general law of treaties as laid down in the VCLT cannot ‘tame’, or regulate, treaty practice. Sometimes, this is simply pragmatic and realistic: a general treaty on treaties can only offer residual rules, just as a general document on responsibility will yield to special regimes (as per Art 55 of the ILC’s Articles on State Responsibility). The VCLT implements the lex specialis principle not in one general clause, but within the specific provisions, many of which contain caveats: Art 28 eg provides for non-retroactivity ‘[u]nless a different intention appears from the treaty or is otherwise established’; Art 54 as the opening provision of Part V Section 3 provides (unsurprisingly) that ‘The termination of a treaty or the withdrawal of a party may take place: (a) in conformity with the provisions of the treaty’. The phrase ‘unless the treaty otherwise provides’ is used 14 times throughout the VCLT. The general law of treaties is residual, and unlike in the case of State responsibility, it is a lex generalis that is very often derogated by special rules.
In other areas, the VCLT provides not residual rules, but no rules at all; and as a result, solutions are sought under other regimes of international law. Duncan rightly mentions remedies, which the VCLT treats rather in passing and which are sought and addressed under the law of dispute settlement, the law of responsibility and/or special treaty regimes. Geir Ulfstein’s reference to treaty bodies to me would also seem to be a case in point: a major element of the multilateral treaty process that is not regulated in any detail by the VCLT’s general rules, but by international institutional law. But questions of responsibility for treaty breaches are probably the biggest ‘regulatory gap’: pursuant to Art 73, the VCLT ‘shall not prejudge any question that may arise … from the international responsibility of a State’. As a consequence, the huge field of treaty breaches, which domestic legal systems often regulate as part of the law of treaties/contracts, is to the regime of international responsibility.
The combined effect of the application of the lex specialis principle and of the conscious decisions of drafters not to cover treaty law issues in their entirety is that quite often, answers to questions of ‘treaty law’ will have to be sought outside the VCLT. This does not affect its status as the key legal instrument in the field. But it means that it has to be read and applied (and presumably taught) in conjunction with other legal texts addressing treaty law issues. And it means that more than with other general legal texts (say, the ILC’s texts on State responsibility or on diplomatic protection; or the 2004 Convention on Jurisdictional Immunities of States and Their Property), the primary treaty law rules in their infinite variety will often determine outcomes. And because of this, Duncan should be congratulated on his decision – explained to contributors right from the start of the project – to complement the legal analysis by a long and detailed part on ‘Treaty Clauses’.