The principle of double effect allows a good action to be
made even though both good and bad results are reasonably
foreseen. The following four conditions must be met before the action which produces both good and evil, may be considered to be a legitimate act.
• The action is morally legitimate. By action we mean
the object, or the act apart from its results.
• The actor intends the good effect only, even though
a bad effect is reasonably foreseen.
• The good effect outweighs the bad effect. The good
caused must be greater than the evil caused.
• The bad effect is unavoidable, and the actor must
take reasonable action to minimize the bad effect.
A textbook example of the principle of double effect would be a fighter pilot intercepting a high jacked airliner which is believed to be on a mission to crash itself into a large building containing a thousand or more people.
The pilot may shoot down the airliner (killing all its occupants), in order to prevent it from crashing into a building and killing even more people…If warning messages, shots, 164
promises and pleas fail; if the target building, or the many possible targets cannot be evacuated.
This decision must not be one in which “a hundred people are killed, in order to prevent the deaths of a thousand.” Such a proposal is not the use of the double effect principle, it would be deliberate murder of a hundred, to save a thousand.
Intention or end is key.
The decision must be “to prevent the high jacked airliner from crashing into a target, (and killing the passengers is an unintended, but unavoidable double effect).” In this allowable decision, we are not swapping one life for ten lives; the deaths of the passengers and crew are not the goal or intention of the act. The only intention here is to stop the aircraft from hitting the building, the unavoidable deaths are allowable by the principle of double effect.131