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I argue that the criterion of just cause is not independent of proportionality and other valid jus ad bellum criteria. One cannot know whether there is a just cause without knowing whether the other (valid) criteria (apart from ‘right intention’) are satisfied. The advantage of this account is that it is applicable to all wars, even to wars where nobody will be killed or where the enemy has not committed a rights violation but can be justifiably warred against anyway. This account also avoids the inefficiency of having proportionality considerations come up at two different points: in a separate criterion of just cause and in the criterion of proportionality proper. ‘Right intention’, the subjective element of the justification of a war, on the other hand, is not to be subsumed under the criterion of just cause: there can be a just cause without anybody knowing it. Conversely, however, the subjective element requires that those responsible for waging the war do know that the justifying objective conditions are fulfilled. This is in one sense more demanding than traditional just war theory; in another sense, however, it is less demanding: nobody needs to intend to fight for a ‘just aim’. Key words