Twenty years ago this week, on 8 July 1996, the International Court of Justice (ICJ) issued an advisory opinion regarding nuclear weapons. In a decision that split its fourteen-member bench, the court found, with the president's casting vote:
[T]he threat or use of nuclear weapons would generally be contrary to the rules of international law applicable in armed conflict, and in particular the principles and rules of humanitarian law; [h]owever, in view of the current state of international law, and of the elements of fact at its disposal, the Court cannot conclude definitively whether the threat or use of nuclear weapons would be lawful or unlawful in an extreme circumstance of self-defence, in which the very survival of a State would be at stake.
This ruling has given rise to divergent positions about the lawfulness of nuclear weapons. Some stand by the notion that there is no room left for their lawful use. On this view, the only thing that is perhaps missing is a treaty confirming their illegality. For many, including myself, international law currently lacks a clear-cut, comprehensive prohibition against their use. This absence is paradoxical, since biological and chemical weapons, the other two weapons of mass destruction, are categorically banned regardless of the circumstances of their use. Still others interpret the advisory opinion as rightly conceding that today's international law permits the use of nuclear weapons in exceptional circumstances.
There is a legal gap
In December 2014, the Vienna conference on the humanitarian impact of nuclear weapons concluded with Austria's observation that "there is no comprehensive legal norm universally prohibiting [their] possession, transfer, production and use". The "Austrian Pledge" - which is also a UN General Assembly resolution now and enjoys the official endorsement of more than 120 states - calls upon states "to identify and pursue effective measures to fill the legal gap for the prohibition and elimination of nuclear weapons".
The "gap" metaphor quickly caught on. In April 2015, two international NGOs active in the field jointly published Filling the Legal Gap: The Prohibition of Nuclear Weapons. They argued that negotiations should commence in 2015 with a view to concluding a ban treaty. When that year's review conference of the Non-Proliferation Treaty (NPT) ended without a final document, a sizable group of states decried a "reality gap, a credibility gap, a confidence gap and a moral gap" in what nuclear disarmament should mean. Those for whom customary international law already prohibits nuclear weapons insist that there is no legal gap but only a "compliance gap" with their prohibition.
There is no legal gap
Resistance to the metaphor has also become increasingly vocal. Let us focus on one of the two senses, i.e., the prohibition of nuclear weapons, in which the existence of a legal gap is contested. (The other sense concerns the content of disarmament obligations under the NPT's Article VI. The United States challenges the notion that there is any legal gap there. So does Italy.)
In April this year, Canada and The Netherlands filed papers with a UN open-ended working group where many participants echoed the need to fill the prohibition gap. The Dutch paper does not specifically deny the "so-called" legal gap. Instead, it quotes the ICJ's 1986 Nicaragua judgment that found that general international law imposes no limitation on the level of armaments of a state. The paper also highlights the 1996 advisory opinion's ambivalence. All we get is the impression that The Netherlands sees no legal gap insofar as "international law does not contain any rule prohibiting nuclear weapons as such".
Canada's position - which it reiterated during the working group meetings - is more explicit. For Canada, "[t]he mere fact that a law or legal norm has not been imposed does not necessarily mean there is a legal gap". While seeking a ban "is an understandable aspiration, the reality is that under current customary international law, the use and possession of nuclear weapons is not illegal". Canada cautions that "legal gap arguments have the potential to be wrongly interpreted as implying there are legal grounds, as opposed to moral or humanitarian grounds, to negotiate a ban on nuclear weapons".
In Canada's view, "a true legal gap requires a situation where the absence of a law or legal norm prevents an inherently 'illegal' situation from being addressed". A New Zealand diplomat succinctly rebutted this mysterious notion called "inherent illegality". Nevertheless, Canada could be implying that a gap exists only where positive law fails to codify what is already forbidden. Since today's customary international law does not ban nuclear weapons per se, the absence of a ban treaty is not a legal gap.
Legal gap or no legal gap - that is not the question
The "no legal gap" argument suggests that the absence of a prohibition does not necessarily mean the absence of a rule. By declining to ban nuclear weapons in all circumstances, international law implicitly permits their use in some circumstances. Permission is a rule, even if it is an implicit one.
This, to be sure, is all very engrossing stuff for lawyers. Delightfully esoteric and full of technical nuances, this line of reasoning raises the kinds of questions on which doctoral dissertations are written and legal careers built. Does today's international law still permit by default what it does not specifically prohibit? Is state survival really a right under international law? Did the ICJ effectively declare non liquet ("the law is not clear") in 1996 and, if so, did it have the authority to do so? The list goes on.
The whole "is there or is there not a legal gap" debate is a bit of a digression, however. For those who see a gap in nuclear weapons' international law status, the gap refers to the absence of their prohibition, not the absence of a rule on their use. Most of us involved in this discussion agree that the law presently lacks a nuclear weapons ban, whether we call it a legal gap or not.
Why, then, would anyone want to mask this agreement? This, I suspect, is because the deniers of a "legal gap" are trying to denigrate the real preoccupation of their opponents. On the one hand, as long as the law contains no gap, there is, by definition, no gap to fill. The world can go back to the usual business of nuclear disarmament in good conscience. On the other hand, admitting a gap's existence would in practice mean admitting the need to fill it. If we successfully prevented the absence of a prohibition of nuclear weapons from being portrayed as a legal gap, that should undercut the ban advocacy's validity.
Advocating a nuclear weapons ban treaty is not an abstract exercise done for some aesthetic reasons ("a gap must be filled because it is there"). Rather, "filling the legal gap" is a figure of speech that helps visualise the lack of a categorical prohibition of nuclear weapons as a problem in need of a solution. The metaphor also highlights prohibition as an item conspicuously missing in the catalogue of effective nuclear disarmament measures proposed by nuclear-armed and umbrella states.
Let us call a spade a spade
In his declaration appended to the ICJ's 1996 advisory opinion, President Bedjaoui warned against those "who will inevitably interpret [the controversial paragraph] as contemplating the possibility of States using nuclear weapons in exceptional circumstances". He continued: "I feel obliged in all honesty to construe that paragraph differently, a fact which has enabled me to support the text".
For those who see a legal gap, filling it simply means introducing a general nuclear weapons ban. For those who do not, international law permits nuclear weapons in some situations. More importantly for them, this permission is in fact a nonissue. No need to fix the law, because it works fine as it is - this, ultimately, is what it means to say that there is no legal gap.