Proportionality in Self-Defence – Proportionate to What?

Abstract

It is a well-settled rule of customary international law that any use of armed force by a state, to be justified as lawful self-defence under either art 51 or customary law, must satisfy various conditions including the essential criteria of necessity and proportionality. This article focuses on the criterion of proportionality, and examines some of the questions concerning its meaning and application - many of which find no definitive answer in ICJ jurisprudence and the literature. It considers questions such as whether actions in response to a past attack, or to forestall a future attack, can be legally characterised as self-defence; the fundamental purpose of self-defence; and ultimately, to what must the action be proportionate.

Keywords: International Law, Customary International Law, Use of Force, Self-Defence, Proportionality

JEL Classification: K10, K30, K33