A relation between opinio iuris and state practice in making customary international law - part II

An explanation for the balance between state practice and opinio juris in the making of customary international law can be found both in legal theory and in the practice of international relations. Nevertheless, it seems to be more effective to seek a cause in the latter. As is implied by the aforementioned judicial quotations, the balance is adequate to a particular category of states’ behaviour. A distinction can be set up according to predominant interests of the international community. In some areas, interests are rather in conflict than concord and usually a competitiveness can be recognized as a key feature. In those areas, because of the very nature of a competition state practice prevails over opinio juris whenever new rules are emerging. In contrast, wherever a wide consent has been reached, opinio juris prevailed at the outset. A cause of this consent is frequently a need for cooperation in certain matters based on rational reasons. In particular, this holds true for the customary rules in international humanitarian law where the opinio juris entirely predominates, ‘even when there is no widespread and consistent state practice, or even no practice at all,’[1] as A. Cassese puts it.

The essence that we can draw from the discussion of this essay is, that being aware of recent trends in the international community we can see their impact on the balance between state practice and opinio juris. As most of natural resources were divided to sovereign states and the remainder was intended for common use and consequently competitiveness receded, the community became more integrated and likely to find common agreement on various matters. Both technical progress and the disaster of the two World Wars contributed to enlarge common needs of the international community. Therefore, triumph of cooperation implied the necessity of the balance to be changed in favour of opinio juris in the making of customary international law.

[1] A. Cassese, International Law (2nd ed. 2005), at 161.