The principle of double effect affects Catholic (and arguably Protestant) moral teaching on subjects from war to abortion, meaning it’s highly relevant to our debates over the use of drone strikes and the tragic death of  Savita Halappanavar . In a nutshell, the principle is that  ”sometimes it is permissible to bring about as a merely foreseen side effect a harmful event that it would be impermissible to bring about intentionally.”

According to twentieth-century analytic philosopher Elizabeth Anscombe, it’s a crucial but easily abused principle—-which makes it all the more worth exploring here. In an essay ( PDF here ) on the ethics of killing the innocent in war, she argues that behind Catholics’ lack of concern on that subject lay “double-think about double-effect.” On the necessity of the principle, she writes:

The distinction between the intended, and the merely foreseen, effects of a voluntary action is indeed absolutely essential to Christian ethics. For Christianity forbids a number of things as being bad in themselves. But if I am answerable for the foreseen consequences of an action or refusal, as much as for the action itself, then these prohibitions will break down. If someone innocent will die unless I do a wicked thing, then on this view I am his murderer in refusing: so all that is left to me is to weigh up evils. Here the theologian steps in with the principle of double-effect and says: “No, you are no murderer, if the man’s death was neither your aim nor your chosen means, and if you had to act in the way that led to it or else do something absolutely forbidden.” Without understanding of this principle, anything can be—and is wont to be—justified, and the Christian teaching that in no circumstances may one commit murder, adultery, apostasy (to give a few examples) goes by the board. These absolute prohibitions of Christianity by no means exhaust its ethic; there is a large area where what is just is determined partly by a prudent weighing up of consequences. But the prohibitions are bedrock, and without them the Christian ethic goes to pieces. Hence the necessity of the notion of double effect.

Yet, she continues, the idea is often mis-applied:
At the same time, the principle has been repeatedly abused from the seventeenth century up till now. The causes lie in the history of philosophy. From the seventeenth century till now what may be called the Cartesian psychology has dominated the thought of philosophers and theologians. According to this psychology, an intention was an interior act of the mind which could be produced at will. Now if intention is all important—as it is—in determining the goodness or badness of an action, then, on this theory of what intention is, a marvellous way offered itself of making any action lawful. You only had to ‘direct your intention’ in a suitable way. In practice this means making a little speech to yourself: “What I mean to be doing is . . . ”

This perverse doctrine has occasioned repeated condemnations by the Holy See from the seventeenth century to the present day . . . .


And in the passage perhaps most relevant to us today:
This same [abuse of double effect] is used to prevent any doubts about the obliteration bombing of a city. The devout Catholic bomber secures by ‘a direction of intention’ that any shedding of innocent blood that occurs is ‘accidental’. I know a Catholic boy who was puzzled at being told by his schoolmaster that it was an  accident  that the people of Hiroshima and Nagasaki were there to be killed; in fact, however absurd it seems, such thoughts are common among priests who know that they are forbidden by the divine law to justify the direct killing of the innocent.

It is nonsense to pretend that you do not intend to do what is the means you take to your chosen end. Otherwise there is absolutely no substance to the Pauline teaching that we may not do evil that good may come.


The four conditions for using the principle in Catholic moral teaching, according to the Stanford Encyclopedia of Philosophy , are:
1. The act itself must be morally good or at least indifferent.
2. The agent may not positively will the bad effect but may permit it. If he could attain the good effect without the bad effect he should do so. The bad effect is sometimes said to be indirectly voluntary.
3. The good effect must flow from the action at least as immediately (in the order of causality, though not necessarily in the order of time) as the bad effect. In other words the good effect must be produced directly by the action, not by the bad effect. Otherwise the agent would be using a bad means to a good end, which is never allowed.
4. The good effect must be sufficiently desirable to compensate for the allowing of the bad effect.

Properly applying the principle to concrete situations, even with such conditions spelled out, will doubtless remain difficult, but I found Anscombe’s essay illuminating. You can read the whole thing here  as a PDF.

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