State practice and the evolution of the law of self-defence: clarifying the methodological debate

Abstract

Self-defence has recently been invoked in order to justify interventions in Syria. This precedent raises the question of the evolution of the law of self-defence in relation to controversial issues such as the right to respond in self-defence to attacks committed by non-state actors and anticipatory self-defence. The aim of this article is less to provide a detailed analysis of this evolution than to reflect on the general conditions under which the law of self-defence may evolve through state practice, especially in relation to such controversial issues. Although state practice is commonly used in legal literature as a means for assessing the evolution of the law of self-defence, scholarship is still quite scarce on the methodological aspects of this evolution through state practice. The article intends to clarify this issue. It first demonstrates that state practice alone is not able to lead to the evolution of the law of self-defence and must be distinguished in that respect from the argument based on the emergence of (new) facts or realities. The article also shows that the conditions for the evolution of the law of self-defence through state practice should vary, not according to the conventional versus customary aspects of that law, but depending upon its evolution through modification or interpretation. It concludes that controversial issues, such as the right to react in self-defence to attacks by non-state actors and anticipatory self-defence, are matters of interpretation rather than modification, and must not therefore meet any too strict requirement to be admitted as part of the current state of the law of self-defence.