doubleeffect

The principle of double effect is a moral doctrine used to evaluate actions that produce two effects: a good effect and a bad effect. It is most closely associated with traditional Catholic moral theology but has been discussed in secular philosophy and modern medical ethics as a framework for justifying certain difficult decisions. The core idea is that an action can be morally permissible even if it has a harmful side effect, provided the harm is not intended, is not the means to the good outcome, and there is a sufficiently grave reason to permit it.

The standard formulation of the principle rests on four conditions. First, the action itself must be morally good or at least morally neutral. Second, the agent must intend only the good effect, with the bad effect foreseen but not intended. Third, the bad effect must not be a means by which the good effect is achieved. Fourth, there must be a proportionately grave reason to permit the bad effect, such that the good effect justifies allowing the harm. The distinction between intention and foreseen consequence is central, as is the requirement of proportionality between the good and bad outcomes.

In practice, the principle is used in medical ethics to analyze end-of-life and treatment choices, such as pain relief that may shorten life or procedures that save one life but risk harming another. Critics argue that the criterion of intention can be vague or subjective and that the line between intended and foreseen effects can be difficult to apply. Some secular ethicists prefer outcome-based or principle-based approaches that do not rely on intention in the same way. See also intention, proportionality, and medical ethics.