Just War theory is the Catholic moral framework for evaluating when the use of military force may be morally justified. The tradition, developed by St. Augustine and refined by St. Thomas Aquinas, holds that war is always a tragedy but may sometimes be a necessary last resort. The Catechism (CCC 2309) lists strict conditions that must ALL be met: (1) The damage inflicted by the aggressor must be lasting, grave, and certain. (2) All other means of resolving the conflict must have been shown to be impractical or ineffective. (3) There must be serious prospects of success. (4) The use of arms must not produce evils and disorders graver than the evil to be eliminated (proportionality). Even in a just war, the principles of discrimination (non-combatants must never be intentionally targeted) and proportionality (force used must be proportionate to the military objective) apply. The Church also recognizes the legitimacy of conscientious objection and calls Christians to work actively for peace.