The Principle of Proportionality under International Law

The principle of proportionality constitutes a legal principle of great importance under the domestic constitutional and administrative laws of many countries. Pursuant to the principle, which strives to balance individual rights and the interests of the general public, many legal systems have introduced important legal constraints on the power of government. The principle of proportionality also fulfills a significant function under international law and restricts the way in which states exercise their powers and rights: human rights law requires states to justify as necessary and proportional every limitation of individual rights; international humanitarian law (the laws of war) contains a number of rules that prohibit excessive injury to civilians and enemy combatants; the laws governing the use of force in international relations permit states to resort to force in self-defense, but require that the application of force be proportionate; and international law regarding state responsibility facilitates the imposition of sanctions against law-breaking states while requiring the proportionality of such sanctions. In all of these cases, the principle of proportionality provides an analytical framework that enables judicial bodies to review the propriety of certain measures on the basis of a value comparison (cost-benefit, violation-sanction). In fact, some regard the principle of proportionality as a general principle of law that governs all fields of international law.

This book aims to examine the status and manner of application of the principle of proportionality under international law. Since the application of the principle under international especially, human rights, use of force and international responsibility. In addition, the principle serves as the underlying rationale for several important rules derived from the laws of war (international humanitarian law), such as the prohibitions against excessive collateral damage and against the use of certain weapons, and restrictions on belligerent reprisals. Still, it seems that the Israeli Supreme Court's ruling in the Security Barrier and Targeted Killing cases – i.e., that the principle constitutes a general principle of international law – does not accurately represent existing law.

In any event, although there is widespread acceptance of the binding nature of the principle of proportionality, international law has yet to succeed in establishing clear guidelines for applying the principle. True, some guidelines may be derived from case law and legal literature – e.g., least harmful measures, adequate procedures for examining the measure's comparative advantages and disadvantages, safeguards against abuse, and protection of the essence of the right. However, these tests  are not universally accepted by all jurists and do not seem to be suitable in every legal context in which the principle of proportionality can be applied. The result of this is that in some critical areas of international law, such as self-defense or targeted killings, the principle of proportionality offers only limited normative guidance.

Despite this, the very ambiguity of the principle supports a careful study of its content in light of past practices and the law affects its application under domestic law, this examination is valuable for both international and national discourse. Indeed, the application of the principle of proportionality under international law has served as the basis of important decisions concerning the route of the separation barrier and the legality of targeted killings, which were issued during the last decade by the Israeli Supreme Court. A critical examination of the compatibility of the aforementioned court decisions with widely held views concerning the status and content of the principle under international law will offer a better understanding of the principle's potential, and of the normative and methodological limits of its application.

The main research questions that this book addresses are:

1. What is the status of the principle of proportionality under international law? Does the principle constitute part of customary law? (This question may be particularly relevant for the purpose of ascertaining the scope of incorporation of the principle in Israeli law, and for determining its applicability to states that are not party to treaties that refer to the principle.) Does the principle constitute a general principle of law that governs every form of interaction between individuals and governments, or does it merely provide a source of inspiration for specific rules of law (which have been adopted in treaties or consolidated into custom)?
2. How is the principle of proportionality applied under international law? Which sub-tests assist in applying the principle? (And what is the status under international law of these sub-tests?) Is the principle comprised of stable elements or does its content change in each specific field of application? What degree of rigidity or flexibility should characterize the application of the principle? (i.e., what margin of discretion – narrow or wide – do states have regarding the application of the principle?)
3. To what extent can the principle of proportionality, as developed under international law, contribute to the development of domestic law, in general, and to the development of Israeli law, in particular?

The research concludes that the principle of proportionality constitutes a principle of customary international law that governs a number of branches of international law –  experience of other decision makers. Therefore, precedents that provide national courts, including Israeli courts, with an important normative perspective on the extensive treatment of the principle at the international level could help them implement this principle in their decisions, either on the basis of international law, or of national law that draws on international law as a comparative source of inspiration.