2 International Customary Law

Custom can more easily be a foundation of universal laws than international treaties. The two requirements that are necessary to be satisfied here are first, that sates in fact do follow the custom (state practice), and second, that they accept it to be necessary a law (opinio juris sive necessiatis; as in Barker 2000: 55). In other words, international custom has to be evidenced by general state practice and at the same time regarded as a binding law in the normative sense. The two elements are often referred to as the objective and subjective (or material and ideational) elements of international custom respectively. State practice is a relatively uncontroversial condition for a custom to be interpreted as a law. State practice includes activity of the organs and officials of states that relate to the possible rule of international law. This means also state practice at the meetings of international organizations (such as the United Nations General Assembly) by voting or otherwise expressing their view on matters under consideration. There are also instances where only what states say can be the evidence of their view on proper conduct in a particular situation (such as in the case of Nicaragua v United States; ICJ Reports #14 in Wikipedia 2006). The practice has to be consistent and regular, but does not have to be perfectly uniform by all states. The second element (opinio juris) is crucial from a normative-theoretical position. One could understand its importance by focusing on the Prisoner’s Dilemma game again. Its’ stable outcome (Nash equilibrium) is a welfare-inferior behavior – that is, defection on the sides of both players. In cases both players know that cooperation strategy is the norm (“law”), and that defection on cooperation is sanctioned in at least some way, then both actors can be better off cooperating with the certainty that also the other player will cooperate. This all allows international law to be not just what states in fact do, and what they would do anyhow (which would then be no rule of law at all), but also what states want to be done. The enforcement of such rules in an anarchical environment is a complicated matter, and it will not be extensively discussed in this paper. It is sufficient to stress that the material element of a custom (state practice or enforcement), being one of the two constitutive parts of this source of law, brings the normative concerns back to reality by proving the viability of certain ideals of behavior. Another important issue in customary law is the necessary duration of state practice and opinio juris for a customary law to be considered legally binding. Several authors speak of the possibility of the so-called “instant custom” (Cheng 1963 in Barker 2000: 57, for example), where only a very short period of time can be sufficient to the formation of a new rule. The two examples Barker (2000) provides include the law of outer space that developed in the later 1950s and early 1960s, and the law governing exclusive economic zones that developed in a decade after 1973. The law on outer space started as a United Nations General Assembly resolution (which is not binding) and was codified only in 1968 with the Treaty on the Principles Governing the Activities of States in the Exploration and Use of Outer Space, […] (Harris 2004: 245-252). This precedence gives to a certain extent of binding power to the UN General Assembly resolutions at the condition that they are followed by practice supported by an opinio juris and thus constitute a customary law. The most renowned cases connected to customary international law are the Asylum case (Columbia v Peru) and the North Sea continental shelf case (Germany v Denmark and The Netherlands). In the Asylum case, a Peruvian rebel was not extradited from Columbia on the ground that Peru repudiated on steps that would constitute such a custom. In the case of the dispute over the North Sea continental shelf, a custom of using an equidistance principle in dividing the seabed among neighboring countries was not found to be a universal practice. Another example of traditionally customary law is that of diplomatic privileges. Many of the former customs, including the diplomatic privileges (1961 Vienna Convention on Diplomatic Relations; Harris 2004: 353), however, have been codified in multilateral treaties, especially in the period after Second World War. This could be interpreted as a declining reliance on customs as rules of the international community.