The Principle of Double Effect

Suppose that you know that an action has two consequences, or effects, one good and one bad. Is it moral to perform that action?

In other words, the harm is FORESEEN -- we expect it to happen, or we understand that there is a strong likelihood that the harm will occur.

Does the fact that we foresee the harm make our action immoral?

The principle of double effect (i.e., multiple consequences) addresses this question.

One can morally do an action with foreseen harmful consequences, provided four conditions are met:

The good effect — but not the evil one — must be directly intended. Any intention to bring about evil corrupts any action. (If you’d do the same thing in a situation that would get the bad effect but not the good one, you’ve violated this condition. You can't be using the good outcome as your excuse for causing the harm.)
Isolated from the two consequences, the action itself must be good, or at least it must be morally neutral. (Donating money to charity is good; using mint toothpaste instead of another flavor is morally neutral.)
The good effect must be produced directly by the agent’s action, and not by means of the evil effect. (If the evil effect causes the good effect, you’ve violated this condition.
There must be a proportionate reason for permitting the foreseen evil effect to occur. (If nothing good will actually be gained, or if the evil will outweigh the good, you’ve violated this condition.)

Both #1 and #4 suggest that the agent must take steps that will minimize the resulting evil or harm.

Here is an example taken from the Stanford Encyclopedia of Philosophy:

"The terror bomber aims to bring about civilian deaths in order to weaken the resolve of the enemy: when his bombs kill civilians this is a consequence that he intends. The strategic bomber aims at military targets while foreseeing that bombing such targets will cause civilian deaths. When his bombs kill civilians this is a foreseen but unintended consequence of his actions. Even if it is equally certain that the two bombers will cause the same number of civilian deaths, terror bombing is impermissible while strategic bombing is permissible."

The classic source of the doctrine is Thomas Aquinas' argument (Summa Theologica, II-II, Qu. 64, Art.7) that we can kill in self-defense: one may use violence against another to save one's own life, even if a consequence of the self-defense will be the death of the aggressor.

This doctrine of double effect is rejected by utilitarians and other consequentialists who deny the moral relevance of intentions. J. S. Mill, for example, denies that good intentions matter.

Notice what happens if we apply the doctrine to cases that involve a harmful cumulative effect of permitting a particular action or behavior.

CUMULATIVE EFFECT: Sometimes we have situations where each individual behavior has good consequences, but where the total result of large numbers of people making the same choice has horrible consequences. For example, very little harm is done to the environment if I realize I'm out of ketchup and I drive to the store before dinner so that I buy some ketchup. However, if large numbers of people own cars and burn gasoline to run trivial errands, we soon have a great deal of pollution and carbon emissions and we have long-lasting harm that is not justified by all the short-term benefits we gained in creating this long-term mess.

Another common example of cumulative effect is that telling one sexist joke at work has little or no effect, but an ongoing pattern of telling sexist jokes constitutes harassment.

Once we recognize that our PATTERN of activity is the problem, and that the cumulative consequences FAIL according to #4 above (the proportionality requirement), then we are no longer morally justified in allowing this behavior. Where large numbers of individuals cannot be trusted to voluntarily coordinate their activities, we must establish and enforce laws that will stop the harmful behavior.

In other words, the doctrine of double effect gives us a principle for social intervention to limit free behavior.

We get a principled reason to support affirmative action, environmental protection laws, and consumer protection laws.

If we return to Aquinas as the source of the doctrine of double effect, then we might also consider his philosophy of justice. For Aquinas, the central idea of justice is to bring it about to "render" to each his own, where "each man's own is that which is due to him according to equality of proportion." (Summa Theologica, II-II, Qu. 58, Art.11) Governments therefore have the duty to enforce restrictions on behavior, such as the Biblical commandment not to commit murder. (Aquinas calls them "negative precepts.") Prohibiting behaviors that harm others is central to justice, because it is unjust to distribute harm to anyone who does not, by their own action, deserve punishment: "all injuries that are inflicted on the person of our neighbor are understood to be forbidden under the head of murder as being the principal of all. ... those that come under the head of damage done to property are understood to be forbidden together with theft" (Summa Theologica, II-II, Qu. 122, Art.6).

Destruction of the environment is not just a sin; our shared environment is also something that governments are morally required to protect.