principle of double effect the view that there is a morally relevant difference between those consequences of our actions we intend and those we do not intend but do still foresee. According to the principle, if increased literacy means a higher suicide rate, those who work for education are not guilty of driving people to kill themselves. A physician may give a patient painkillers foreseeing that they will shorten his life, even though the use of outright poisons is forbidden and the physician does not intend to shorten the patient’s for all definite values of p, including the probability case just given. If we allow that some (significant) statements have no truth-value or probability and distinguish external negation ‘Tp’ from internal negation ‘T-p’, we can distinget may accept as inevitable, without intending to bring about, the deaths of a number of civilians. Traditional moral theologians affirmed the existence of exceptionless prohibitions such as that against taking an innocent human life, while using the principle of double effect to resolve hard cases and avoid moral blind alleys. They held that one may produce a forbidden effect, provided (1) one’s action also had a good effect, (2) one did not seek the bad effect as an end or as a means, (3) one did not produce the good effect through the bad effect, and (4) the good effect was important enough to outweigh the bad one.
Some contemporary philosophers and Roman Catholic theologians hold that a modified version of the principle of double effect is the sole justification of deadly deeds, even when the person killed is not innocent. They drop any restriction on the causal sequence, so that (e.g.) it is legitimate to cut off the head of an unborn child to save the mother’s life. But they oppose capital punishment on the ground that those who inflict it require the death of the convict as part of their plan. They also play down the fourth requirement, on the ground that the weighing of incommensurable goods it requires is impossible.
Consequentialists deny the principle of double effect, as do those for whom the crucial distinction is between what we cause by our actions and what just happens. In the most plausible view, the principle does not presuppose exceptionless moral prohibitions, only something stronger than prima facie duties. It is easier to justify an oblique evasion of a moral requirement than a direct violation, even if direct violations are sometimes permissible. So understood, the principle is a guide to prudence rather than a substitute for it.
See also ETHICS, EUTHANASIA , INTENTION , JUST WAR THEOR. P.E.D.