The Principle of Double Effect has been with us since the Middle Ages and has sanctified actions that might otherwise be viewed as morally wrong. What I wish to show in this brief perspective is that an overlooked element in the discussions of this principle raises a serious question about its applicability.

The principle is invoked in those circumstances in which an individual's action has two consequences: one that the agent can foresee and is purportedly good, the other that he can also foresee and is purportedly bad. For Thomas Aquinas, it permitted an individual to defend himself against physical attack, even if such an action resulted in the death of the assailant. For today's physician, it permits him to provide pain-killing morphine, even if he can foresee that the accumulated dosages may be sufficient to kill the patient. The question is, does this principle, in fact, resolve such dilemmas?

The four conditions of the Principle of Double Effect are

1. 1) The action in itself must be good or morally neutral

2. 2) The good effect and not the bad effect is intended

3. 3) The good effect is not produced by means of the bad effect

4. 4) There is a proportionately important reason for permitting the bad effect.

If a physician satisfies these conditions while giving morphine to a terminally ill patient who is suffering severe, chronic pain, he is, according to the principle, acting morally.

In order to determine whether his action is, in fact, morally correct, can we confidently assert that the physician has met these requirements? There are two considerations that indicate that we cannot do so: One is based on the inability of the physician to determine his own intention; the other is based on our inability to determine what the physician's intention is.

Let us look at the first consideration. The physician may believe that his intention is only to ameliorate the pain. But he can be deceiving himself. His desire to deal with the extreme and chronic pain of his terminally ill patient by shortening his life can conflict with the opposing strictures of the law or with the policies of his professional association. Yet the physician cannot ignore the possibility of his patient dying, as it figures in the calculations he must make in titrating the morphine that he administers. A conflict of this sort can result in the physician repressing his unacceptable and tabooed intention and then “act in good faith” in helping his patient. The physician may claim to be acting only to ameliorate the patient's pain when, in fact, he unconsciously intends that the morphine will shorten the life of his patient. My claim is not that every physician has such a desire, but rather that he may not be able to tell which of the two possible intentions (or perhaps both) is operative.

The fact that we, as observers, are unable to determine a physician's intentions is my second reason for denying the applicability of the Principle of Double Effect. Suppose that our physician believes that euthanasia is morally permissible when a patient is dying and in great pain. He cannot openly operate in terms of this belief, given the law and the social or professional taboos against euthanasia. But he can violate condition two, and possibly condition three, of the Principle of Double Effect by claiming to offer the morphine in order to ameliorate the pain, but hope that it will bring about the death of his patient. Under these circumstances, we would be unable to discover the physician's true intention.

What I have attempted to demonstrate in this short analysis is that in the sorts of situations in which the Principle of Double Effect is relevant, either self-deception or the deception of others is a genuine possibility. In the first instance, neither honesty nor careful introspection serves as a guarantee against mistaken belief. In the second instance, a deception can be carried out by the same means as an act of nondeception. Thus, it follows that if neither we nor the physician is able to determine his true intention in treating a patient with morphine, then at least one of the conditions of the Principle of Double effect is inapplicable. In this circumstance, there is no alternative to assessing the morality of the physician's action except in terms of its consequences.