Advisory Opinion of Legality of the Threat or Use of Nuclear Weapons
(ICJ Reports 1996, p. 226)

(Constituent elements of custom; General Assembly Resolutions as one of the sources of international law)

(The General Assembly requested the International Court of Justice to provide an advisory opinion on the following question: ‘Is the threat or use of nuclear weapons in any circumstance permitted under international law?’)

The Court will now turn to an examination of customary international law to determine whether a prohibition of the threat or use of nuclear weapons as such flows from that source of law. As the Court has stated, the substance of that law must be “looked for primarily in the actual practice and opinio juris of States” (Continental Shelf (Libyan Arab Jarnahiriya/Malta), Judgment, 1. C. J. Reports 1985, p. 29, para. 27).

States which hold the view that the use of nuclear weapons is illegal have endeavoured to demonstrate the existence of a customary rule prohibiting this use. They refer to a consistent practice of non-utilization of nuclear weapons by States since 1945 and they would see in that practice the expression of an opinio juris on the part of those who possess such weapons.

Some other States, which assert the legality of the threat and use of nuclear weapons in certain circumstances, invoked the doctrine and practice of deterrence in support of their argument. They recall that they have always, in concert with certain other States, reserved the right to use those weapons in the exercise of the right to self-defence against an armed attack threatening their vital security interests. In their view, if nuclear weapons have not been used since 1945, it is not on account of an existing or nascent custom but merely because circumstances that might justify their use have fortunately not arisen.

The Court does not intend to pronounce here upon the practice known as the “policy of deterrence”. It notes that it is a fact that a number of States adhered to that practice during the greater part of the Cold War and continue to adhere to it. Furthermore, the members of the international community are profoundly divided on the matter of whether non-recourse to nuclear weapons over the past 50 years constitutes the expression of an opinio juris. Under these circumstances the Court does not consider itself able to find that there is such an opinio juris.

According to certain States, the important series of General Assembly resolutions, beginning with resolution 1653 (XVI) of 24 November 1961, that deal with nuclear weapons and that affirm, with consistent regularity, the illegality of nuclear weapons, signify the existence of a rule of international customary law which prohibits recourse to those weapons. According to other States, however, the resolutions in question have no binding character on their own account and are not declaratory of any customary rule of prohibition of nuclear weapons; some of these States have also pointed out that this series of resolutions not only did not meet with the approval of all of the nuclear-weapon States but of many other States as well.

States which consider that the use of nuclear weapons is illegal indicated that those resolutions did not claim to create any new rules, but were confined to a confirmation of customary law relating to the prohibition of means or methods of warfare which, by their use, overstepped the bounds of what is permissible in the conduct of hostilities. In their view, the resolutions in question did no more than apply to nuclear weapons the existing rules of international law applicable in armed conflict; they were no more than the “envelope” or instrumentum containing certain pre-existing customary rules of international law. For those States it is accordingly of little importance that the instrumentum should have occasioned negative votes, which cannot have the effect of obliterating those customary rules which have been confirmed by treaty law.

The Court notes that General Assembly resolutions, even if they are not binding, may sometimes have normative value. They can, in certain circumstances, provide evidence important for establishing the existence of a rule or the emergence of an opinio juris. To establish whether this is true of a given General Assembly resolution, it is necessary to look at its content and the conditions of its adoption; it is also necessary to see whether an opinio juris exists as to its normative character. Or a series of resolutions may show the gradua1 evolution of the opinio juris required for the establishment of a new rule.

Examined in their totality, the General Assembly resolutions put before the Court declare that the use of nuclear weapons would be “a direct violation of the Charter of the United Nations; and in certain formulations that such use “should be prohibited”. The focus of these resolutions has sometimes shifted to diverse related matters; however, several of the resolutions under consideration in the present case have been adopted with substantial numbers of negative votes and abstentions; thus, although those resolutions are a clear sign of deep concern regarding the problem of nuclear weapons, they still fall short of establishing the existence of an opinio juvis on the illegality of the use of such weapons.

The Court further notes that the first of the resolutions of the General Assembly expressly proclaiming the illegality of the use of nuclear weapons, resolution 1653 (XVI) of 24 November 1961 (mentioned in subsequent resolutions), after referring to certain international declarations and binding agreements, from the Declaration of St. Petersburg of 1868 to the Geneva Protocol of 1925, proceeded to qualify the legal nature of nuclear weapons, determine their effects, and apply general rules of customary international law to nuclear weapons in particular. That application by the General Assembly of general rules of customary law to the particular case of nuclear weapons indicates that, in its view, there was no specific rule of customary law which prohibited the use of nuclear weapons; if such a rule had existed, the General Assembly could simply have referred to it and would not have needed to undertake such an exercise of legal qualification.

Having said this, the Court points out that the adoption each year by the General Assembly, by a large majority, of resolutions recalling the content of resolution 1653 (XVI), and requesting the member States to conclude a convention prohibiting the use of nuclear weapons in any circumstance, reveals the desire of a very large section of the international community to take, by a specific and express prohibition of the use of nuclear weapons, a significant step forward along the road to complete nuclear disarmament. The emergence, as lex lata, of a customary rule specifically prohibiting the use of nuclear weapons as such is hampered by the continuing tensions between the nascent opinio juris on the one hand, and the still strong adherence to the practice of deterrence on the other.

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