Just War

Thomas Aquinas – Just War Theory from Summa Theologiae II-II, q. 40.

War is justified (nation A wars justly against nation B) on the following conditions:

  • A. It is called by a sovereign authority.
  • B. It has a just cause.
  • C. The combatants have right intentions.
  • D. Qualifying Conditions (from the theory of double-effect from his justification of killing in self-defense: ST II-II, 64, 7).
    1. Cannot intend intrinsically evil actions.
    2. A good action, or at least a morally neutral action, can have two effects: a good intended, and an evil, not intended, but tolerated.
    3. Proportionality the good to be achieved outweighs the evil of war.

A. A Just War must be called by a sovereign authority. It is a nation (not individuals) who declares war.

  1. wars are just when they are in defense of the common goods.
  2. the sovereign has care for the common good (of a particular nation)

B. Just Cause

  1. Thomas Aquinas addresses causes which concern the nation (nation A) itself.
    a. An enemy (nation B) is attacked because they deserve it.
    b. The enemy is guilty of some fault.
    c. A nation may war justly
    i. To avenge a wrong.
    ii. Punish enemy for refusing to make amends for some past fault.
    iii. To restore what was seized unjustly.
  2. Later thinkers have expanded the notion of just cause. (See ‘The Just War’ by Jonathan Barnes in The Cambridge History of Later Medieval Philosophy (1982), pp. 771-785.
    a. Is war justified when someone other than the warring nation suffered from an enemy’s unjust aggression?
    i. Friends and allies: Nation A may justly war on nation B to defend nation C. (See Thomas Aquinas, ST II-II, 188, 3 ad 1)
    ii. The inhabitants of the enemy’s country.
    a) St. Thomas More (1535) – Yes, war may be justified for humanitarian reasons.
    b) Francisco Suarez (1617) – No, such a war violates the sovereignty of the other nation and will lead to international chaos.
    b. There has not been any actual aggression from the enemy, but the nation has reason to fear that there is a threat of an attack.
    i. Francisco de Vitoria (1546) – No, wars are just only when redressing actual injustice.
    ii. Francis Bacon (1626) – Yes, just fear is a lawful cause for war.
    iii. Hugo Grotius (1645) – To threaten one’s neighbors is an actual injustice; it is aggression against peaceful order between nations.

C. The combatants in a just war must have right intentions.

  1. advancement of good and the avoidance of evil.
  2. unjust reasons include
    a. Greed.
    b. Cruelty.
    c. Vengence
  3. just reasons include
    a. Secure peace
    b. Punish evil-doers.
    c. Uplifting of good.

D. Qualifying Conditions – from the justification of self-defense and the theory of double-effect.

  1. Cannot intend intrinsically evil actions: Combatants must respect non-combatants.
    a. Combatants who cease to be so.
    i. Surrendering
    ii. Wounded
    b. Cannot target civilians.
    i. Civilian casualties, while foreseeable, cannot be intended.
    ii. Measures must be taken to minimize civilian casualties.
  2. Proportionality the good to be achieved outweighs the evil of war.
    a. One cannot war justly over a slight cause.
    (i. War is a last resort.)
    (ii. There must be a reasonable chance of success; one cannot engage in justified, but hopeless actions.)
    b. One may only use the minimal force necessary to achieve just ends.

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