We may list here the conditions, as presented in the Catechism, for the legitimate use of military force (2309):
– the damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain;
– all other means of putting an end to it must have been shown to be impractical or ineffective;
– there must be serious prospects of success;
– the use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modern means of destruction weighs very heavily in evaluating this condition
We will proceed through each of these with brief comment, but for the moment it is necessary to take notice of the words preceding this list in the Catechism, “At one and the same time,” are of great import to our reasoning. The conditions set forth are not to be used in an “either…or” process of reasoning. One, or even two, of the conditions may be met, but this does not justify military force. All conditions must be met, or we must exclude military force as a just course of action.