The Respective Roles of Custom and Principle in the International Law of Armed Conflict

This paper was presented as the Second Friedrich Martens Memorial Lecture inMay 2007. It takes a critical view of the current frequent reference to custom as asource of the law of armed conflict and suggests that in many cases one shouldmore properly speak of the general principles of law. While some norms of the lawof armed conflict may not necessarily reflect “general practice accepted as law”,they may still be recognized as binding on account of their inner force and on thebasis of what may be referred to as communis opinio juris. The author advances the view that the existence of such communis opinio can beestablished by means of a threefold test. Thus, in order to be considered a principleof the law of armed conflict, a norm must (1) have a modicum of support on thepart of States, for instance in the shape of a reflection in military manuals, (2)reflect widely recognized core values of humanity, and (3) enjoy broad support ininformed international discourse (e.g., in Red Cross and Red Crescent conferences,in academic circles etc.). These requirements reflect, in effect, the three sourceslisted cumulatively in the Martens Clause: “the usages established among civilisednations, the laws of humanity, and the dictates of the public conscience.”