Doctrine of Double Effect

The Doctrine of Double Effect is an ethical principle that is used to explain how certain actions that would cause considerable harm can be morally permissible where the bringing about of such harm is a side effect of the promotion of some good end. This principle is usually invoked by ethicists who subscribe to a deontological, or rule-based, approach to ethics, especially those who subscribe to the Judeo-Christian ethical tradition. (Indeed, Thomas Aquinas is credited with developing the first formulation of this Doctrine in his discussion of self-defense in the Summa Theologica.) Such ethicists are unwilling to hold that the good that could be brought about by the infliction of such harm would itself justify the bringing about of the harm, as would, for example, a utilitarian ethicist.

According to the proponents of the Doctrine of Double Effect, four conditions must be met in order for it to be justly invoked to explain the moral permissibility of an act whose performance would cause harm as a side effect. First, the act itself must be morally good or at least morally neutral. Second, the agent performing the act must not intend the bad effect, but must merely foresee that it would occur as a result of his action. Third, the good effect that is intended must be produced directly by the act that the agent performs; it cannot be produced through the bad effect. That is, the bad effect cannot be used as a means to secure the good effect; it can only flow from the agent's act as a corollary effect of it. Finally, the good effect must be proportionate to the bad effect.

To illustrate this, consider an example where a developer builds a housing project, knowing that to do so will have the side effect of causing environmental damage as a result of the increase in fuel emissions from the increased use of cars in the vicinity. According to the proponents of the Doctrine of Double Effect, the developer is permitted to build the housing project, even if his doing so will lead to environmental damage, provided that he only intends to build the houses and merely foresees such damage occurring. The building of houses is itself a morally neutral act, the bad effect is foreseen but not intended, the good effect is not produced through the building of the houses; this is merely a corollary to the developer's act, and the badness of the environmental damage is outweighed by the goodness of providing housing.

The Doctrine of Double Effect is, however, subject to the criticism that there is no more than a semantic distinction between what is foreseen and what is intended in the cases where the Doctrine is invoked. Thus, when the developer above builds his houses he must intend to do, and not just foresee, environmental damage, since the two effects are inherently linked. As such, it is argued, the core distinction of the Doctrine is untenable.