The Principle of Double Effect

3. Four Key Objections

3.3 Problem 3: Misses Core of Morality

By not recognising that some consequences of voluntary actions are foreseen but unintended, absolutism misses the core of morality.

Even if the distinction between acts and consequences is made, advocates of the Principle of Double Effect will say that problems will remain unless we distinguish between the foreseen and intended consequences of a voluntary act, on the one hand, and the foreseen but unintended consequences on the other. For some absolutists to lump together, for example, all foreseen deaths consequent to voluntary acts as 'intentional' is to ignore that which is of central importance to morality. PDE proponents argue that it is the intended consequences of a person's voluntary actions, as opposed to the unintended but foreseen consequences, that is indicative of his moral character and integrity.

To illustrate this line of reasoning, consider these three actions permitted by PDE under an absolutist ethic that prohibits the killing of an innocent person.

  1. A man makes a breach in a dike that is about to break in order to avert sudden destruction of a whole town, knowing that as a consequence of his act two people will drown.[4]
  2. A group of people locked in a room find a time-bomb and throw it out of a single window in order to save their lives, seeing that it will land near a man below who will be unable to escape.[5]
  3. A doctor knowingly injects a possibly lethal dose of morphine into a terminally ill patient in order to relieve him of pain, but not desiring his death. The patient subsequently dies of an overdose.

According to the advocates of PDE, although killing has occurred in all three cases, the acts are not morally blameworthy because the foreseen deaths of the victims were unintended. In all of these cases, all four conditions for application of PDE (§2 above) are satisfied.

Some critics of PDE have argued that PDE does not even get off the ground because the claimed distinction between intended and unintended foreseen consequences of voluntary actions is mistaken. These critics claim that all such foreseen consequences are intended.[6] I think that these critics are mistaken for the reason that although there are some consequences that are difficult to determine whether they are intended or not, other cases are clear. The dentist who extracts a tooth from his patient does not intend the resulting pain. The cancer therapist who treats a patient with X-ray therapy does not intend for their hair to fallout. The man who gets drunk does not intend to have his next morning's hangover.[7]

Book cover: Utilitarianism by John Stuart Mill

The proponent of PDE is correct in isolating the intention of moral agents as being morally relevant to moral evaluation, at least in many cases, and PDE's distinction between intended and unintended consequences is a significant improvement over the absolutist ethic that makes no such distinction. However, I do not think that the intentions of moral agents are relevant in the ways specified by PDE. As a preliminary observation, it seems that not all foreseen but unintended consequences should avoid blame. The driver that accidently kills a pedestrian because he was too lazy to have his faulty brakes repaired, knowing full well that such a consequence was likely to occur, is not absolved from blame for the death of the victim because his death was unintended.

As Thomson [1973: 152f] has argued, to properly determine whether an intention to produce bad effects is a necessary indicator of the moral status of an action, what is needed is a comparison between two situations in which the only relevant difference is that in one the foreseen bad consequence is intended, while in the other it is unintended. In that vein, consider the case[8] of two doctors, each practising in a country that permits voluntary euthanasia and that has enacted laws to safeguard against abuse. Further, suppose that each doctor is treating a terminally ill patient who is suffering constantly and who has made repeated, considered requests for a peaceful death. In each case, the doctor has administered a large dosage of a pain killing drug that is the minimum necessary to relieve pain, knowing, however, that the patient will certainly die of an overdose.

The single difference between the two circumstances is that in one situation, the doctor did not intend the death of the patient, merely seeking to relieve his pain, while in the other, the doctor intended the patient's death as a means of providing permanent relief from unbearable pain. As the first-mentioned doctor satisfies all four conditions of the application of PDE, his unintended killing is permitted. Applying PDE to the second situation, the intentional killing of the patient is deemed blameworthy.

It could be argued on humanitarian grounds, however, that there is no moral distinction between the two acts of killing. If one were forced into making some moral distinction, I think that a good case could be made out for morally appraising the second-mentioned doctor more than the first. This could be argued on the basis that the second- mentioned doctor's humanitarian intentions are worthy of reinforcement for the greater benefit of future patients. For these reasons, it seems prudent to conclude that condition 2 of PDE, that the agent must not intend the bad effect, is misdirected.

Similarly, condition 3, that the good effect must not be a product of the bad effect, seems also to be mistaken. The second-mentioned doctor's act fails to satisfy condition 3 because the good effect, the permanent relief from unbearable pain, is only obtained by means of the bad effect, the patient's death. However, if there is no moral distinction between the first-mentioned doctor's act and that of the second, condition 3 is unwarranted.[9] So, although the Principle of Double Effect is an improvement over absolutist ethics that make a too simple analysis of intention, the principle fails to resolve satisfactorily the problems of such a rudimentary analysis. And this is because it misplaces the relevance of intentions in moral evaluation.


  1. [4] This scenario is presented by Williams [1974: 199f].
  2. [5] This scenario is presented by D'Arcy [1966: 172].
  3. [6] See, for example, Williams [1974: 203]. See also Bentham [1823: ch. 8, ¶6].
  4. [7] The most comprehensive and worthwhile attempt at characterising an intentional action that I have seen is that by Kenny [1968: 154]. An intentional action, according to Kenny, is one in which the agent a) knows he is doing it and b) wants to do it either for its own sake or in order to further some other end.
  5. [8] Thomson has her own very instructive example in her [1973: 153f].
  6. [9] For further example scenarios, see Frey [1975]. See also Thomson's example in her [1973: 153f], which also violates condition 3. Williams' example, in Smart and Williams [1973: 98f], of a man who must intentionally kill one person to save the lives of ten others is also a case of a violation of conditions 2 and 3 if the man decides to shoot, even though I think that his intentional killing of the one person is morally defensible.

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