The Principle of Double Effect and the Atomic Bombings of WWII

Catholic moral theologians have consistently held that the atomic bombings of Hiroshima and Nagasaki by the United States during World War II were gross violations of justice. The Church herself has taught this:

"Every act of war directed to the indiscriminate destruction of whole cities or vast areas with their inhabitants is a crime against God and man, which merits firm and unequivocal condemnation." A danger of modern warfare is that it provides the opportunity to those who possess modern scientific weapons—especially atomic, biological, or chemical weapons—to commit such crimes (CCC 2314).

The Church and human reason assert the permanent validity of the moral law during armed conflicts. Practices deliberately contrary to the law of nations and to its universal principles are crimes (CCC 2328).

A basic philosophical argument that can be offered for this conclusion is as follows:

1. Intentionally killing non-combatants is unjust.
2. The atomic bombings of WWII intentionally killed non-combatants.
3. Therefore, the atomic bombings of WWII were unjust.

To the argument that the bombings saved more lives than would have otherwise been preserved in the absence of the bombings, the reply must be made that the ends do not justify the means. We cannot do evil that good may come (cf. Romans 3:8). A basic argument rooted in this Pauline principle can be given as follows:

1. We cannot use an evil means to achieve a good end (Romans 3:8).
2. The atomic bombings of WWII constituted the use of evil means (viz., the killing of non-combatants) to achieve a good end (viz., ending the war and minimizing casualties).
3. Therefore, the atomic bombings of WWII were illicit.

The best way to go about refuting these arguments would be to attack the second premises in each. Let's focus on the first argument. One way to challenge the truth of its second premise would be to appeal to the principle of double effect (henceforth, PDE), a well-established principle of Catholic moral theology. St. Thomas Aquinas succinctly formulates the PDE and applies it to the issue of personal self-defense as follows:

Nothing hinders one act from having two effects, only one of which is intended, while the other is beside the intention. Now moral acts take their species according to what is intended, and not according to what is beside the intention, since this is accidental... Accordingly, the act of self-defense may have two effects, one is the saving of one's life, the other is the slaying of the aggressor. Therefore this act, since one's intention is to save one's own life, is not unlawful, seeing that it is natural to everything to keep itself in being, as far as possible. And yet, though proceeding from a good intention, an act may be rendered unlawful, if it be out of proportion to the end. Wherefore if a man, in self-defense, uses more than necessary violence, it will be unlawful: whereas if he repel force with moderation his defense will be lawful, because according to the jurists, it is lawful to repel force by force, provided one does not exceed the limits of a blameless defense. Nor is it necessary for salvation that a man omit the act of moderate self-defense in order to avoid killing the other man, since one is bound to take more care of one's own life than another's (ST II-II, 64, 7).

A more fleshed out formulation of the PDE can be given as follows:

It is lawful to perform an action from which an evil effect is foreseen when the following conditions are present:

1. the action willed itself must be good or at least indifferent; for clearly, if the action is bad, it is also unlawful;
2. a good effect must also follow from the act, and it must not be caused by the evil effect; for the end does not justify the means. Thus, it is not lawful to take what belongs to others in order to give alms, for the evil effect (stealing) results from the act (taking) immediately; whereas the good effect (almsgiving) results only mediately through the theft;
3. the agent must intend only the good effect, since it is unlawful to wish evil. Thus, if one foresees that one's virtuous life will cause the sin of envy in a neighbor, this evil result of one's virtue must not be entertained by one as something pleasing;
4. the agent must have a reason sufficiently weighty for permitting the evil result that follows his act. Evil should not even be permitted, unless there is adequate compensation in the good that is intended (Moral Theology: A Complete Course, Vol. I, par. 104, pg. 55).

With respect to the atomic bombings of World War II, one might try to apply the PDE as follows: The act is the bombing of a city. Now, bombing a city is not intrinsically evil. Suppose that a city is old and abandoned and people want to destroy it so that a new city can be erected in its place. This clearly seems to be morally permissible. Thus, the first condition of the PDE is satisfied. Skipping over the second condition for now, the third condition is likely satisfied. Presumably, the United States did not aim at the mass killing of Japanese civilians—though this was obviously foreseen—but rather the sole intent was to secure peace and minimize casualties by swiftly ending the war. Thus, the second premise of the first argument is false. The fourth condition is also plausibly satisfied. There was a sufficiently weighty reason for permitting the evil effect, namely, ending the most horrific and deadly war that humanity had ever faced.

But what about the second condition? Here is where the application of the PDE to the present case fails. For the evil effect in this case—the mass killing of Japanese civilians and the destruction of Hiroshima and Nagasaki—was the cause of Japan surrendering and thus ending the war. Hence, the second condition of the PDE fails in this case. Consequently, the PDE cannot successfully justify the atomic bombings of World War II. Furthermore, it is a stretch to say that the intention was not to kill civilians when an atomic bomb was dropped on a civilian city. If the killing of civilians was not intended as an end, it was at least intended as a means, and an evil means cannot be justified by a good end (cf. Romans 3:8). At the very least, therefore, the second argument is sound. Therefore, we may conclude that the atomic bombings of World War II were immoral and unjust.