Proportionality in International Law

In the most general terms proportionality requires a balance to be drawn between frequently conflicting values. Consequently, its application depends on a subjective value judgment and that very indeterminacy sometimes sits uneasily within law. Proportionality, nevertheless, is a pervasive and familiar concept within both the civil and criminal national legal systems of states. The norm first found expression in international law in the doctrine of the just war, the Christian version of which formed the basis of the secular just war writings of early commentators on the developing discipline of international law, such as Grotius and de Vattel. Nowadays the principle is reflected either explicitly or implicitly in several diverse areas of international law. It appears explicitly as either a treaty norm—as, for example, in the regulation of targeting decisions in International Humanitarian Law (IHL)—or as a customary norm in the case of self-defense and Countermeasures. In other situations, proportionality operates as a judicial mechanism of review implicit in the need to balance competing interests such as in European Union Law (EU Law), International Human Rights Law (IHRL), and the dispute settlement regime of the World Trade Organization (WTO). Proportionality is also a component of Maritime Law and Delimitation, the Law of Treaties, and International Criminal Law (ICL). The norm even has considerable support as constituting that elusive concept, a general principle of international law. The significance and scope of its role varies widely depending on the area of international law in question and determines to a considerable extent the amount of literature available on the topic. Despite its increasing importance in international law, exactly what proportionality requires of a particular decision maker in any given area of international law remains unsettled and is the subject of widespread judicial and scholarly debate. There is no one meaning of proportionality that is common in all contexts in which it operates or any consensus as to its application across the board. In order to provide some structure to the debate scholars have identified two major analytical approaches to the application of proportionality that they see reflected in state practice and jurisprudence: the so-called “quantitative” approach where the response is tailored or equivalent to the action against which it is to be measured, and the so called “qualitative” approach where other factors are to be taken into account. It is not suggested in the literature that all practice fits neatly into one or other category, but they are useful for the purposes of analysis and much of the material that follows incorporates these concepts.