The Court qualified its statement by holding that ‘the Court cannot conclude definitely 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’. However, as the Court reminded, a “fundamental” and “intransgressible” rule is that:
"States must never make civilians the object of attack and must consequently never use weapons that are incapable of distinguishing between civilian and military targets".

It is near impossible for any contemplated use of nuclear weapons to meet this criteria as they are weapons of mass destruction. As the Court explained: ‘(i)n view of the unique characteristics of nuclear weapons, .... the use of such weapons in fact seems scarcely reconcilable with respect for (humanitarian) requirements’. Moreover, as Judge Bediaoui, President of the Court, has observed, the qualification is merely a statement of uncertainty in the light of legal and factual materials available before the Court. He stated: ‘I cannot sufficiently emphasize the fact that the Court’s inability to go beyond this statement of the situation can in no manner be interpreted to mean that it is leaving the door ajar to recognition of the legality of the threat or use of nuclear weapons’.

The Court also considered, among other things, the evidence highlighting the irretrievable damage the use of nuclear weapons would cause to the environment and held:
"...that while the existing international law relating to the protection and safeguarding of the environment does not specifically prohibit the use of nuclear weapons, it indicates important environmental factors that are properly to be taken into account in the context of the implementation of the principles and rules of the law applicable in armed conflict".

It stressed in this regard the ‘general obligation to protect the natural environment against widespread, long-term and severe environmental damage; the prohibition of methods and means of warfare which are intended, or may be expected, to cause such damage; and the prohibition of attacks against the environment by way of reprisals’. Therefore, read as a whole the general illegality conclusion of the Court is overpowering. It perhaps deserves mention that both in the context of adhering to humanitarian laws and preventing environmental damage the nuclear weapon states failed to make a case before the Court that a “limited” use of nuclear weapons was either feasible or comply with humanitarian law or avoid catastrophic escalation.

Having pronounced the general illegality of the threat or use of nuclear weapons the Court went on to unanimously hold that:
"...there exists an obligation to pursue in good faith and bring to a conclusion negotiation leading to nuclear disarmament in all its aspects under strict and effective international control".

It observed that nuclear disarmament is ‘an objective of vital importance to the whole of the international community’. The Court explained that Article VI of the Nuclear Non-Proliferation Treaty (NPT) imposes an obligation to achieve a precise result nuclear disarmament in all its aspect- by adopting a particular course of conduct, namely, the pursuit of negotiations on the matter in good faith’. This unanimous opinion which requires states to not simply talk but act is among the most important aspect of the advisory opinion of the ICJ.

The Court refrained from pronouncing upon the practice known as the policy of deterrence. However, it is of interest that India in its written submission before the Court stated as follows:

"Nuclear deterrence had been considered to be abhorrent to human sentiment since it implies that a state if required to defend its own existence will act with pitiless disregard for the consequences to its own and adversary’s people .... A better and saner way to secure everlasting peace would be to ensure that (not) only are such weapons never used but also not made.
...Since the production and manufacture of nuclear weapons can only be with the objective of their use, it must follow that if the use of such weapons itself is illegal under international law, then their production and manufacture cannot under any circumstances as permitted. Besides, the manufacture and stockpiling of nuclear weapons would constitute a threat of their eventual use".

Several decades ago Einstein had observed that ‘the splitting of the atom has changed everything except our modes of thinking, and thus we drift toward unparalleled catastrophe’. The decision of the ICJ goes a long way towards changing the terms of discourse by delegitimising nuclear weapons. Its opinion given at the request of the General Assembly of the United Nations goes the furthest it can in declaring the threat or use of nuclear weapons as illegal under international law. While the opinion of the Court is not formally binding on the States it has offered an authoritative interpretation of the law which states have the moral duty to comply with.