Is the NPT Customary International Law?: A Question Central to the Marshall Islands ICJ Case

I was just reading Avner Cohen’s recent piece on the Marshall Islands case over at the BAS website. In it Cohen writes:

The lawsuit reflects a growing belief among international legal and policy experts (as well as some diplomats) that the time has come for the NPT to be treated—due to its near universal adherence—as part of customary international law by which all states must abide, regardless of whether or not they actually signed the treaty.

Based on this reasoning, the Marshall Islands asks the International Court of Justice to rule that all nine nuclear states are in material breach of their legal obligation to disarm under international law, regardless of their status under the NPT. Currently the international community does not consider the NPT to be part of international customary law; if it were, the treaty would have a legal status similar to that of the international bans on slavery or torture. Should the International Court of Justice make such a ruling, it could elevate the discourse on nuclear disarmament from vague declarations of intentions to stark statements of legally binding commitment.

Cohen is certainly right to identify the question of whether the NPT, or at least Article VI of the NPT, is part of customary international law, as a central question in the Marshall Islands (RMI) case. It is the argument on which the entirety of the RMI’s case against those of the nine potential respondents who are not parties to the NPT, rests. But I thought I would try to provide some clarity to Cohen’s discussion of this question.

The question of whether the NPT, in whole or in part, has entered into customary law is one that has been knocking around in international legal discourse for a long time. I’ve talked with colleagues at conferences about the subject for many years, though as far as I know there has not yet been a focused treatment published on this question. I know some people over the years have told me they were working on one, but I have yet to see it in print. If there is such a treatment out there, I would be happy to have attention drawn to it in the comments.

Generally speaking, broadly-subscribed-to treaties, such as the NPT, are fertile ground for potentially finding that a process sometimes referred to as parallel customary law creation has occurred. This simply means that, even if the principles codified in the treaty were not, prior to codification, a part of customary international law, the very fact of their codification, and even more importantly the subsequent implementation of these principles by states parties, under the (quite correct) impression that these principles are legally obligatory upon them, satisfies the two elements of state practice and opinio juris that together turn a principle into a rule of customary international law.

This phenomenon is quite common in the international legal system. Examples include principles of the 1977 Additional Protocols to the Geneva Conventions on the Law of Armed Conflict, principles of the 1969 Vienna Convention on the Law of Treaties, and principles of the 1982 UN Law of the Sea Convention. In each of these contexts, states who are not parties to the treaties themselves, have recognized that, while the treaty per se is not binding on them, some of the principles codified in the treaty have, through parallel state practice and opinio juris, become rules of customary international law which are binding on them through that separate source of international law.

These examples are also illustrative of another characteristic of parallel customary law, which is that customary law development parallel to a treaty is not an all-or-nothing proposition. In each of the examples cited above, it is only some of the principles codified in the treaty that are considered to have entered into the corpus of customary international law. Not necessarily all of them. This is why, for example, the ICRC’s study on customary law in the law of armed conflict is so important – it is a rigorous analysis of which of the principles codified in the Geneva Conventions and their Additional Protocols have entered into CIL. And that study found that the substance and definitions of the obligations as between the treaty and CIL differs significantly.

So let’s now come back to the NPT. In my 2009 book I wrote that the NPT had not, at least in toto, entered into customary international law, unlike the CWC and the BWC:

On a normative development level as well, the contract treaty nature of the NPT has not given the elements of customary law creation clear universal principles to attach to, in order to enable the creation of parallel custom, unlike in the cases of the Chemical Weapons Convention (CWC) and the Biological Weapons Convention (BWC), to be discussed in detail below. Such parallel customary law in the cases of these other multilateral nonproliferation treaties constitutes an important supplemental source of legal obligation through which even non-parties, and particularly secondary proliferators of WMD technologies, may be bound to the terms of the cornerstone international legal instruments.

I still think that this analysis is correct. However, there are some articles of the NPT that are worded in such a way as to comprise universal obligations upon all states parties to the treaty, notwithstanding they are a part of the treaty’s quid pro quo structure of obligations. The most important of these are Articles IV & VI of the treaty.

As I’ve already explained, there is no problem legally with having individual articles or provisions of a treaty pass into customary international law, even if the entirety of the treaty in which they are found does not. So the question I think becomes, is there sufficient evidence of state practice and opinio juris to support the conclusion that either or both Article IV or Article VI have become principles of customary international law?

Focusing on Article VI, as that is the operative provision in the Marshall Islands case, this basically becomes an empirical question. The tests for state practice and opinio juris are well expressed and defined in international legal sources, and what is needed is a focused study evaluating state practice, and inferences about the sense of legal obligation under which states have taken that action, in order to answer the question of whether the principles in Article VI have indeed been established as customary law. If they have been, then this hugely strengthens the RMI’s case against the four non-NPT parties in the cases.

As I said above, I have not personally conducted such an empirical study. I don’t know if anyone has. If they have, I would invite them to come forward and enlighten us!

But I will give my own sense, which is admittedly anecdotal and qualitative at this point, just from viewing the landscape of state practice and opinio juris on this question through statements made at NPT PrepComs and RevCons, etc. for some time now.

I would conclude that there are indeed a sufficient number of states who consider the obligation in Article VI of the NPT to be a binding legal obligation, and who have acted in conformity with that opinio juris, over a sufficient amount of time, with sufficient consistency, in order to establish the Article VI obligation as an obligation of customary international law, in addition to its codification in the NPT.

It must be remembered that perfect universal conformity with a rule, or recognition of the rule as binding, is not necessary for customary law to form. As the ICJ itself said in the 1986 Nicaragua case:

It is not to be expected that in the practice of States the application of the rules in question should have been perfect, in the sense that States should have refrained, with complete consistency, from the use of force or from intervention in each other’s internal affairs….the Court deems it sufficient that the conduct of States should, in general, be consistent with such rules, and that instances of State conduct inconsistent with a given rule should generally have been treated as breaches of that rule, not as indications of the recognition of a new rule.

So the fact that there are among the NWS especially, states that do not view the Article VI obligation to in fact be a binding legal obligation, does not per se mean that it is not a binding obligation, nor that it has not entered into customary law. Looking to statements of the Non-Aligned Movement, which represents a supermajority of states, as well as to the 2010 NPT Review Conference Final Document, as I did in some detail in my 2011 book, I think there is ample evidence of opinio juris to support the conclusion that the Article VI obligation is a part of customary international law, even if the NPT in its entirety is not.

This is obviously going to be a highly contentious part of the RMI’s case, particularly against India and Pakistan, who as I wrote previously are two of the only three states (along with the UK) over whom the ICJ likely does have jurisdiction to proceed with this case.


10 Comments on “Is the NPT Customary International Law?: A Question Central to the Marshall Islands ICJ Case”

  1. Dan Joyner says:

    I’ve just been having an email conversation with someone. I won’t mention their name, but they wrote:

    “It can’t be customary international law if a number of states consistently object, a situation which I believe obtains in the case of Article VI. There must be plenty of statements by the P-5 that Article VI is aspirational and does not create immediate obligations to do more than pursue a long-term goal.”

    I responded as follows:

    “I think that you are incorrect in the standard you are applying to the formation of CIL. Please note the quote from the ICJ in the Nicaragua case that I excerpted in my post. If a supermajority of states display sufficient state practice and opinio juris, CIL will form even if a minority of states object. Now, if individual states object sufficiently they can establish themselves as persistent objectors to the rule. This means that they individually are not bound by it. But it does not stop the rule from coming into being. Furthermore, persistent objector status is very difficult to achieve and I doubt very much that it has been achieved by any of the nuclear weapons possessing states. They may argue that point, and it may be an issue before the court, but I doubt that they will succeed.”

  2. masoud says:

    Dear Dan,

    Am I wrong in my belief that this is the first time in history adherence to Article VI of the NPT is being demanded through an international legal forum? If so how can we say that states have acted as if Article VI or more specifically, the principle that building and maintaining Nuclear arsenals is illegal, is a binding legal obligation?

    As far as I am aware, none of the NWS have ever faced any international sanction, either through international tribunals, or unilateral or multilateral action for their ongoing nuclear arsenal buildup. And out of the non-signatory states that have developed nuclear arsenals, only North Korea has faced any kind of continued objection. India and Pakistan briefly faced international scorn for developing international arms, but the nuclear programs of both countries have been subsequently legitimized through the removal of the initial sanctions, followed by a sharp uptick in nuclear cooperation with a variety of singnatories to the NPT.

    Israel’s nuclear arsenal has been outright praised and sheltered from the very start by at least a significant minority of European states, even though it has been opposed by groups like the NAM.

    But, I’ve thought about it a little bit, and there does seem to be some points the other side of this argument too. Ironically, the strongest evidence I can think of that would tend to favor interpreting the principles of Article VI as a biding legal obligation, are:
    1. The UNSC resolutions and sanctions against Iraq, as well as it’s invasion by the US, primarily on the suspicion that it might be continuing to develop nuclear arms. And that this concern was typically given more prominence by the UNSC and the US than concerns that it might be developing chemical and Bbological arms, both of which, I think, are banned under CIL.
    2. The many UNSC resolutions against Iran, under the pretext that Iran might be pursuing nuclear arms.
    3. The IAEA BOG resolutions calling on Iran to take steps, even ‘beyond the Additional Protocol’ to demonstrate that it isn’t building nuclear arms, as well as it’s highly irregular finding of non-compliance against Iran after it had declined to do so.
    4. The many IAEA DG reports to the BOG, regretting that he is unable to certify that ‘all fissionable materials’ are ‘in peaceful use’, even though the DG lacks any other apparent legal framework to make such an evaluation.
    5. The many unilateral sanctions issued by the US and the EU against Iran for said reasons.
    6. The overt compliance with said unilateral sanctions by banks all over the world.
    7. The international sanctions campaign against Lybia before it abandoned it’s legal program, and it’s immediate reintegration in the western economic fold after it did.
    8. Israel’s attacks on Osiriak in Iraq, and al-Kibar, the justifications Israel gave for these actions, and the lack of any serious international sanctions that Israel has subsequently felt.

    So it seems that almost every state that has at times acted as though article VI isn’t really binding has at some other points acted as if it extremely binding. Seems like more of wash than I first realized when I started this comment.

    Or at least that’s my uninformed two cents.

  3. masoud says:


    I’ve got another question or two for you, or anyone else out there in the know that has the time.

    In an earlier post, you mentioned that the US and most of the other P5 countries will only recognize the jurisdiction of the ICJ on a case by case basis. I believe you said GB was the only exception

    I’m trying to out how this is supposed to work. The US, for example, is listed as an original member of the ICJ. Therefore any member state of the NPT should be able to bring suit against it for not living up to it’s NPT obligations. Did it issue whatever the treaty equivalent of a signing statement is, while doing so? ICJ website’s primer on this says, among other things:

    (e) The Court itself decides any questions as to its jurisdiction

    Article 36, paragraph 6, of the Statute provides that in the event of a dispute as to whether the Court has jurisdiction, the matter shall be settled by the decision of the Court. Article 79 of the Rules lays down the conditions which govern the filing of preliminary objections.

    How is this particular circle squared? How would the P5 be able to get away from the ICJ jurisdiction even if none of the provisions of the NPT have entered CIL?

    Is there a case to be made that on CIL matters touching on international peace and security, or WMD, the necessity of recognizing the jurisdiction of of the ICJ has itself entered CIL?

  4. EmmaP says:

    I like Masouds two cents worth, indeed the whole discusion, and no mention of oil anywhere……

  5. Chloe Sommers says:

    Hi there, I stumbled upon your post as I was researching whether the NPT in totality or at least Article II of the NPT falls into the category of customary international law. I am conducting this research based on the 2018 Jessup International Moot Court Competition problem, which deals with a fictional State with essentially the same status and circumstances as India (with regards to the NPT). If you’re interested, here’s a link to the problem.

    Thank you for this article, and any insight as to the CIL status of Article II in recent years would be much appreciated!

    • Dan Joyner says:

      Hi Chloe, I’m very familiar with the Jessup problem. I’m the faculty advisor for the Alabama team! They’re just finishing up writing their memorials, as I’m sure you are too. I hope you found these debates useful to your research. Good luck in the competition.

  6. […] conventionalisation of nuclear weapons invites their advancement, which is hardly in line with the (allegedly customary) obligation of nuclear disarmament under Article VI of the NPT. States are not in compliance with […]

  7. […] conventionalisation of nuclear weapons invites their advancement, which is hardly in line with the (allegedly customary) obligation of nuclear disarmament under Article VI of the NPT. States are not in compliance with […]

  8. […] conventionalisation of nuclear weapons invites their advancement, which is hardly in line with the (allegedly customary) obligation of nuclear disarmament under Article VI of the NPT. States are not in compliance with […]

  9. Melvin says:

    It’s a pity you don’t have a donate button! I’d without a doubt donate to this outstanding blog!
    I guess for now i’ll settle for bookmarking and adding
    your RSS feed to my Google account. I look forward to fresh updates and will talk about this site with my Facebook group.
    Chat soon!

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s