ABSTRACT
The right of self-defense recognized expressly in Article 51 of the UN Charter and by customary law allows every state to respond with force to an illegal armed attack on it provided such force is necessary and proportionate. Legitimate self-defense also embraces collective self-defense, a concept expressly included in Article 51. Article 51 authorizes self-defense “if an armed attack occurs.” The majority of governments and scholars consider that this means “only if an armed attack occurs.” Some commentators, such as Derek Bowett and Stephen Schwebel, have argued to the contrary, mainly on the ground that customary law allowed force in response to a threat of attack and that this was safeguarded as the “inherent right” referred to in Article 51. “Necessity” and “proportionality” are conditions of self-defense that depend largely on the particular circumstances of the situation in question. Collective self-defense allows a state to come to the aid of another state that has been illegally attacked.
