Israel Law Review


The Proportionality Principle in Operation: Methodological Limitations of Empirical Research and the Need for Transparency

Aaron Fellmetha1

a1 Professor, Arizona State University College of Law (email:


The principle of proportionality, notoriously obscure in application and subjective in interpretation, has been enforced so rarely as to call into question its potency as a meaningful international legal standard. Nonetheless, international criminal tribunals, academics, and the ICRC's monumental study on customary international humanitarian law all confidently proclaim the principle as embedded in the customary international law applicable to both international and non-international armed conflicts. To assess whether these claims are accurate, and to flesh out how states interpret the principle in practice, the author and a colleague have undertaken a long-term, multinational empirical study of state practice in interpreting and enforcing the proportionality principle. This article discusses the methodological options available and explains the one chosen for the proportionality study. The limitations of the study, in spite of its deliberate methodology, suggest that the debilities of the proportionality principle may not be conceptual as much as a byproduct of unnecessary military secrecy. This article concludes that greater transparency in state compliance with the rule of discrimination and the principle of proportionality would, at least, facilitate an understanding of how the hitherto obscure principle operates in practice and, at best, could create systemic effects that would decrease the dangers to civilians in armed conflicts.

(Online publication March 05 2012)


  • law of war;
  • international humanitarian law;
  • proportionality;
  • transparency;
  • empirical research


The author thanks Yaël Ronen and the staff of the Israel Law Review for helpful comments on an earlier draft of this article.