Principle of Double Effect
The Principle of Double Effect was introduced by St. Thomas Aquinas in cases of self-defense. In general, the Principle states that an action that has both a bad and a good effect is morally permissible providing:
- The action in and of itself is morally good or neutral.
- The bad effect is not intended either as a means or as an end.
- The bad effect is not disproportionate in badness in relation to the value of the good effect.
For instance, a vaccine manufacturer typically knows that while a vaccine will save many lives, a few people will die from side-effects of taking the vaccine. The manufacturing of a drug is in itself morally neutral (assuming no unethical research practices are used, workers are compensated fairly, etc.). The bad effect--the deaths due to side-effects--does not further any goals the drug manufacturer has, and hence is not intended as a means to anything. Nor is the bad effect intended as an end in and of itself. Finally, the number of lives saved is much greater than the number lost, and so the proportionality condition is satisfied.
The Principle appears useful in war situations. In a just war, it may be morally acceptable to bomb the enemy headquarters to end the war quickly, even if civilians on the streets around the headquarters might die. For, in such a case, the bad effect of civilian deaths is not disproportionate to the good effect of ending the war quickly, and the deaths of the civilians are not intended by the bombers, either as ends or as means. On the other hand, to bomb an enemy orphanage in order to terrorize the enemy into surrender would be unacceptable, because the deaths of the orphans would be intended, in this case as a means to ending the war early, contrary to condition (2). Whether the Principle applies to the bombing of Hiroshima and Nagasaki is a highly controverted question.