On the alleged customary nature of Article VI of the NPT – A Rejoinder to Joyner and Zanders

Both Dan and Jean-Pascal offer excellent counterarguments in their replies to my blog post on the customary nature of Article VI, and I thank them for this.

After thinking carefully about their comments, I would like to offer some further thoughts.

1) I think that there is no obstacle in principle for a single provision within a treaty to be taken in isolation to establish whether it has become customary international law. The severability of treaty provisions finds support in the Vienna Convention on the Law of Treaties and has been upheld, for instance, in the ICJ Nicaragua Judgment, where the Court examined whether Articles 2(4) and 51 of the Charter reflected customary international law. We could even say that we should sometimes look at whether individual paragraphs within a provision are customary: again, in the Nicaragua case, the ICJ concluded that only the first sentence of Article 51 was a reflection of customary international law but not the second, ie the duty to report the armed reaction in self-defence to the Security Council. True, Article VI is linked to the other pillars of the NPT and is part of that Grand Bargain. But we shouldn’t forget that customary international law has a life of its own, independent from the treaty from which it may have originated: therefore, nothing prevents that only certain provisions of the NPT may have become customary but not others, even though, in the treaty where they were originally contained, they were intended as a package deal.

2) Like Jean-Pascal, I am not sure that the Chemical Weapons Convention is an appropriate analogy with the NPT. Indeed, as Jean-Pascal says, the difference between the NPT and the CWC is that the latter doesn’t distinguish between haves and have-nots. But an even more important difference is that virtually all states parties (and non-parties as well) agree that the use and possession of chemical weapons is unlawful: those states that are suspected of possessing or using them don’t count as contrary practice, as they don’t argue that such situations are lawful, rather they normally deny possession or use (Syria docet) or argue that the chemicals used don’t fall within the definition of the prohibited weapons, therefore confirming the prohibitory rule.

3) Dan is of course correct to say that Article VI formally addresses all NPT states parties. I still think, however, that this provision ‘specially’ affects only those states that possess nuclear weapons, as their position is necessarily different from that of non-nuclear weapon states. The fact that Article VI was what the NNWS asked to the NWS in return for their giving up the right to possess nuclear weapons (as Dan rightly states) demonstrates that this provision was specifically aimed at the NWS. In my view, it’s also impossible for the NNWS to engage in the relevant conduct, ie to give up weapons they don’t possess: they could engage if they acquired nuclear weapons, but that would confirm my argument, ie that the provision only specially affects states once they possess nuclear weapons.

4) I agree with Jean-Pascal that the customary nature of a provision or of a whole treaty doesn’t necessarily depend on how many states have ratified that treaty. Rather, it depends on the attitude of the states not parties in relation to that treaty. I also agree with Sergei Batsanov when he says in his comment to my initial post that we also have to take into account the practice of the several NNWS that accept nuclear weapons on their territory and of those that benefit of the nuclear deterrence umbrella. This practice by NNWS seems to imply an opinio that is difficult to reconcile with the customary nature of Article VI, ie it’s based on the acceptance that certain states may possess nuclear weapons.

To conclude. While I would in principle agree that Article VI, as a treaty provision, may have been breached by the NWS (although doubts about the normativity of this provision remain), I am still not sure that, at this stage, it reflects customary international law. The empirical study wisely advocated by Dan would have to provide evidence of consistent practice and opinio juris in that sense by a sufficiently representative majority of states, including the majority of the specially affected states (as per the North Sea Continental Shelf Judgment).