38 for the operations of irregular corps and thus ensure that there was someone to hold accountable if they did not act in accordance with the laws and customs of war. 115 94. In other words, States have in practice accepted that belligerents may use paramilitary units and other irregulars in the conduct of hostilities only on the condition that those belligerents are prepared to take responsibility for any infringements committed by such forces. In order for irregulars to qualify as lawful combatants, it appears that international rules and State practice therefore require control over them by a Party to an international armed conflict and, by the same token, a relationship of dependence and allegiance of these irregulars vis-à-vis that Party to the conflict. These then may be regarded as the ingredients of the term “belonging to a Party to the conflict”. 95. The Appeals Chamber thus considers that the Third Geneva Convention, by providing in Article 4 the requirement of “belonging to a Party to the conflict”, implicitly refers to a test of control. 96. This conclusion, based on the letter and the spirit of the Geneva Conventions, is borne out by the entire logic of international humanitarian law. This body of law is not grounded on formalistic postulates. It is not based on the notion that only those who have the formal status of State organs, i.e., are members of the armed forces of a State, are duty bound both to refrain from engaging in violations of humanitarian law as well as - if they are in a position of authority - to prevent or punish the commission of such crimes. Rather, it is a realistic body of law, grounded on the notion of effectiveness and inspired by the aim of deterring deviation from its standards to the maximum extent possible. It follows, amongst other things, that humanitarian law holds accountable not only those having formal positions of authority but also those who wield de facto power as well as those who exercise control over perpetrators of serious violations of international humanitarian law. Hence, in 115 Military Prosecutor v. Omar Mahmud Kassem et al., 42 International Law Reports 1971, p. 470, at p. 477. The court consequently held that the accused, members of the PLO captured by Israeli forces in the territories occupied by Israel, did not belong to any Party to the conflict. As the court put it (ibid., pp. 477-478): “In the present case [... n]o Government with which we are in a state of war accepts responsibility for the acts of the Popular Front for the Liberation of Palestine. The Organisation itself, so far as we know, is not prepared to take orders from the Jordan[ian] Government, witness[ed by] the fact that [the Organization] is illegal in Jordan and has been repeatedly harassed by the Jordan[ian] authorities.” Case No.: -94-1-A 15 July 1999