Double effect (Ethics)

The principle of double effect – also known as the rule of double effect, the doctrine of double effect, often abbreviated as DDE or PDE, double-effect reasoning, or simply double effect – is a set of ethical criteria which Christian philosophers have advocated for evaluating the permissibility of acting when one's otherwise legitimate act may also cause an effect one would otherwise be obliged to avoid. The first known example of double-effect reasoning is Thomas Aquinas' treatment of homicidal self-defense, in his work Summa Theologica. This set of criteria states that, if an action has foreseeable harmful effects that are practically inseparable from the good effect, it is justifiable if the following are true: the nature of the act is itself good, or at least morally neutral; the agent intends the good effect and does not intend the bad effect, either as a means to the good or as an end in itself; the good effect outweighs the bad effect in circumstances sufficiently grave to justify causing the bad effect and the agent exercises due diligence to minimize the harm.