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World Court Digest

I. Substantive International Law - First Part
2.2. Customary International Law
2.2.1. Formation of Customary International Law

¤ Legality of the Threat or Use
of Nuclear Weapons
Advisory Opinion of 8 July 1996
I.C.J. Reports 1996, p. 226

[pp. 253-255] 65. States which hold the view that the use of nuclear weapons is illegal have endeavored 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.
66. 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-defense 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.

67. 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.
68. 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.
69. 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.
70. 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 gradual evolution of the opinio juris required for the establishment of a new rule.

71. 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 juris on the illegality of the use of such weapons.
72. 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.
73. 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.

[p. 277 Decl. Shi] In my view, "nuclear deterrence" is an instrument of policy which certain nuclear-weapon States use in their relations with other States and which is said to prevent the outbreak of a massive armed conflict or war, and to maintain peace and security among nations. Undoubtedly, this practice of certain nuclear-weapon States is within the realm of international politics, not that of law. It has no legal significance from the standpoint of the formation of a customary rule prohibiting the use of nuclear weapons as such. Rather, the policy of nuclear deterrence should be an object of regulation by law, not vice versa. The Court, when exercising its judicial function of determining a rule of existing law governing the use of nuclear weapons, simply cannot have regard to this policy practice of certain States as, if it were to do so, it would be making the law accord with the needs of the policy of deterrence. The Court would not only be confusing policy with law, but also taking a legal position with respect to the policy of nuclear deterrence, thus involving itself in international politics which would be hardly compatible with its judicial function.

[p. 309 S.O. Fleischhauer] The practice embodied in the policy of deterrence is based specifically on the right of individual or collective self-defense and so are the reservations to the guarantees of security. The States which support or which tolerate that policy and those reservations are aware of this. So was the Security Council when it adopted resolution 984 (1995). Therefore, the practice which finds expression in the policy of deterrence, in the reservations to the security guarantees and in their toleration, must be regarded as State practice in the legal sense.

[pp. 314-315 D.O. Schwebel] What does the practice of such possession of nuclear weapons thus import? Nuclear Powers do not possess nuclear arms to no possible purpose. They develop and maintain them at vast expense; they deploy them in their delivery vehicles; and they made and make known their willingness to use them in certain circumstances. They pursue a policy of deterrence, on which the world was on notice when the NPT was concluded and is on notice today. The policy of deterrence differs from that of the threat to use nuclear weapons by its generality. But if a threat of possible use did not inhere in deterrence, deterrence would not deter. apossession by the five nuclear Powers is lawful until the achievement of nuclear disarmament; if possession is the better part of deterrence; if deterrence is the better part of threat, then it follows that the practice of States - including their treaty practice - does not absolutely debar the threat or use of nuclear weapons.

Thus the régime of the Non-Proliferation Treaty constitutes more than acquiescence by the non-nuclear States in the reality of possession of nuclear weapons by the five nuclear Powers. As the representative of the United Kingdom put it in the oral hearings,

"The entire structure of the Non-Proliferation Treaty presupposes that the parties did not regard the use of nuclear weapons as being proscribed in all circumstances."

To be sure, the acquiescence of most non-nuclear-weapon States in the fact of possession of nuclear weapons by the five nuclear Powers – and the ineluctable implications of that fact - have been accompanied by vehement protest and reservation of rights, as successive resolutions of the General Assembly show. It would be too much to say that acquiescence in this case gives rise to opinio juris establishing the legality of the threat or use of nuclear weapons. What it - and the State practice described - does do is to abort the birth or survival of opinio juris to the contrary.

[pp. 319-320 D.O. Schwebel] The General Assembly has no authority to enact international law. None of the General Assembly's resolutions on nuclear weapons are declaratory of existing international law. The General Assembly can adopt resolutions declaratory of international law only if those resolutions truly reflect what international law is. If a resolution purports to be declaratory of international law, if it is adopted unanimously (or virtually so, qualitatively as well as quantitatively) or by consensus, and if it corresponds to State practice, it may be declaratory of international law. The resolutions of which resolution 1653 is the exemplar conspicuously fail to meet these criteria. While purporting to be declaratory of international law (yet calling for consultations about the possibility of concluding a treaty prohibition of what is so declared), they not only do not reflect State practice, they are in conflict with it, as shown above. Forty-six States voted against or abstained upon the resolution, including the majority of the nuclear Powers. It is wholly unconvincing to argue that a majority of the Members of the General Assembly can "declare" international law in opposition to such a body of State practice and over the opposition of such a body of States. Nor are these resolutions authentic interpretations of principles or provisions of the United Nations Charter. The Charter contains not a word about particular weapons, about nuclear weapons, about jus in bello. To declare the use of nuclear weapons a violation of the Charter is an innovative interpretation of it ' which cannot be treated as an authentic interpretation of Charter principles or provisions giving rise to obligations binding on States under international law. Finally, the repetition of resolutions of the General Assembly in this vein, far from giving rise, in the words of the Court, to "the nascent opinio juris", rather demonstrates what the law is not. When faced with continuing and significant opposition, the repetition of General Assembly resolutions is a mark of ineffectuality in law formation as it is in practical effect.

[p. 424 D.O. Shahabuddeen] To sum up, putting at the highest all of the matters relied on by the proponents of legality, the Court could find that those matters do not suffice to cancel out the continuing assertion of the proponents of illegality that the threat or use of nuclear weapons is illegal. It would follow that the basic difficulties noticed above would remain. If, as I consider, a correct finding is that, on the law as it stood at the commencement of the nuclear age, a prohibitory rule then existed, that finding, as to what was the then law, cannot be contradicted by subsequent inconsistent State practice; the most that subsequent inconsistent State practice could do would be to generate a new rule rescinding, or modifying the old rule. But the position taken by most of the NNWS1 would make it impossible to establish that the necessary opinio juris emerged to support the creation of a new rule having the effect of reversing the old, and more particularly if the latter had the status of jus cogens. The prior prohibitory rule would thus continue to the present time.

1Non-Nuclear Weapon States