1. In a recent important contribution to the literature on euthanasia, the whole of one of the seven chapters was dedicated to the doctrine: Williams, G.Intention and Causation in Medical Non-Killing. London: Routledge; 2007.
2. For example, Cavanaugh, TA.Double-Effect Reasoning: Doing Good and Avoiding Evil. Oxford: Clarendon Press; 2006; McGee, A.Finding a way through the ethical and legal maze: Withdrawal of medical treatment and euthanasia. Medical Law Review 2005;13:357–85.
3. Seale, C.National survey of end-of-life decisions made by UK medical practitioners. Palliative Medicine 2006;20:3–10. But see Forbes, K, Huxtable, R.Clarifying the data on double effect. Palliative Medicine 2006;20:395–6.
4. Joseph Fins, responding to the charge that the doctrine of double effect was too scholarly to be useful, replied: “I can’t imagine a world at the end of life without double effect. We’d be highly impoverished without it, and patients would suffer needlessly without it. We do need our philosophical contrivances in order to be pragmatic physicians and caregivers.” Cited in New York Times, 27 Dec 2009; available at http://www.nytimes.com/2009/12/27/health/27sedation.html?_r=1&em=&pagewanted=all.
5. See note 2, Cavanaugh 2006.
6. Huxtable, R.Get out of jail free? The doctrine of double effect in English law. Palliative Medicine 2004;18:62–8.
7. The title of Quinn’s foundational article illustrates this simple definition. Quinn, W.Actions, intentions, and consequences: The doctrine of double effect. Philosophy and Public Affairs 1989;18(4):334–51.
8. Fathers of the English Dominican Province, translators, Summa Theologica of Saint Thomas Aquinas. New York: Benziger Bros.; 1947. Section 2 of part 2, question 64, article 7, body. In keeping with standard notation for Aquinas’s texts, the Summa will hereafter be cited as ST and references will note its particular section and part (1a, 1a2ae, 2a2ae, 3a) question (q.) article (a.), and part of article. Parts of an article are indicated by obj. (objectio—preliminary argument—usually numbered), sed contra (counterargument), resp. (responsio, body of argument), ad 1, ad 2, and so forth (replies to preliminary arguments as numbered).
9. Awareness of effects outside of intention—and allowance for them—does not originate with Aquinas. For instance, cities of refuge are prescribed in the Hebrew Bible “so that a slayer who kills a person without intent may flee there.” The Holy Bible. New Revised Standard version. New York: Oxford University Press; 1991. Numbers 35:11. The case law that follows in Numbers 35:16–34 takes into account the difference between premeditated murder and manslaughter.
10. See note 8, ST 2a2ae, q. 64, a. 7, resp. See also ST 1a2ae q. 12 a. 1, “Whether intention is an act of the intellect or the will?”
11. See note 8, ST 2a2ae, q. 64, a. 8, resp.
12. See note 8, ST 2a2ae, q. 64, a. 8, sed contra.
13. It is common for implications to be attributed to Thomas as original doctrine. See Jordan, MD.Rewritten Theology; Aquinas after His Readers. Oxford: Blackwell; 2006. But Thomas’s purpose, central theme, and principle of organization for the Summa is set out at its beginning: “The chief aim of sacred doctrine is to teach the knowledge of God, not only as He is in Himself but also as He is the beginning of things and their last end, and especially of rational creatures. …[O]ur endeavor [is] to expound this science.” See note 8, ST 1a, q. 2. See also ST 1a, q. 44, aa. 1; 3; 4, ad 4. See also Mangan, JT.An historical analysis of the doctrine of double effect. Theological Studies 1949;X(I):44–6.
14. See note 8, ST 1a2ae, q. 18, “Of the good and evil of human acts in general.” See Kaczor, C.Double-effect reasoning from Jean Pierre Gury to Peter Knauer. Theological Studies 1998;59:299.
15. “Whether a human action is good or evil from its end? … Nothing hinders an action that is good in one of the way mentioned above, from lacking goodness in another way. And thus it may happen that an action which is good in its species or in its circumstances is ordained to an evil end, or vice versa.” See note 8, ST 1a2ae, q. 18, a. 4, ad 3.
16. “Whether the good or evil of a man’s action is derived from its object? … It is written (Osee 9:10): ‘They became abominable as those things which they loved.’ Now man becomes abominable to God on account of the malice of his action. Therefore the malice of his action is according to the evil objects that man loves. And the same applies to the goodness of his action.” See note 8, ST 1a2ae, q. 18, a. 2, sed contra.
17. Aquinas relies here on Aristotle’s notion of virtue and practical wisdom: “The Philosopher says (Ethic. ii, 3) that a virtuous man acts as he should, and when he should, and so on in respect of the other circumstances.” See note 8, ST 1a2ae, q. 18, a. 3, sed contra. See all of a. 3: “Whether man’s action is good or evil from a circumstance?” ST 1a2ae, q. 18, a. 10, “Whether a circumstance places a moral action in the species of good or evil?” and ST 1a2ae, q. 6, a. 3, “Whether there can be voluntariness without any act?”
18. Gury, JP.Compendium Theologicae Moralis, 2 vols. Regensburg, Germany: F Pustete; 1874:1.8.
19. Ugorji, LI.The Principle of Double Effect: A Critical Appraisal of Its Traditional Understanding and Its Modern Reinterpretation. Frankfurt, Germany: Peter Lang; 1985:33.
20. See note 14, Mangan 1949:43.
21. “Why not say—as we are being slanderously reported as saying and as some claim that we say—‘Let us do evil that good may result’? Their condemnation is deserved.” See note 9, Bible 1991. Romans 3:8.
22. Knauer, P. The hermeneutical function of the principle of double effect. In: Curran, CE, McCormick, RA, eds. Readings in Moral Theology 1: Moral Norms and Catholic Tradition. New York: Paulist Press; 1979:1.
23. See note 22, Knauer 1979:16.
24. See note 14, Kaczor 1998:59, 297–317; Boyle, J.Medical ethics and double effect: The case of terminal sedation. Theoretical Medicine 2004;25:51–60.
25. Although many of its formulations depend on an assessment of a result being “good” or “bad,” and a moral worldview that rejected such assessments would not be able to use the doctrine. Wenkel, D.Separation of conjoined twins and the principle of double effect. Christian Bioethics 2006; 12:291–300.
26. Keown, J.Euthanasia, Ethics and Public Policy. Cambridge, UK: Cambridge University Press; 2002:20. See also note 7, Quinn 1989.
27. Warren Quinn, for instance, puts great store on the idea that double effect “distinguishes between agency in which harm comes to some victims, at least in part, from the agent’s deliberately involving them in something in order to further his purpose precisely by way of their being so involved (agency in which they figure as intentional objects), and harmful agency in which either nothing is in that way intended for the victims or what is so intended does not contribute to their harm.” See note 7, Quinn 1989. See also Foot, P.The problem of abortion and the doctrine of double effect. Oxford Review 1967;5:5–15.
28. Michael Walzer argues for beneficiaries accepting additional risk if this will minimize harm. His original case has to do with civilian and pilot risk, contending that pilots should accept increased likelihood of being shot down if a lower altitude would minimize inaccuracies in bombing. Walzer, M.Just and Unjust Wars. New York: Basic Books; 1977:151–9.
29. The example is from Catholics United for the Faith, a lay organization whose mission is “to support, defend, and advance the efforts of the Teaching Church in accord with the teachings of the Second Vatican Council.” As such, they can be taken as a representative Catholic view. Available at http://www.cuf.org/about/mission.asp (last accessed 28 Oct 2010).
31. For example, Williams, G.Intention and Causation in Medical Non-Killing. London: Routledge; 2007:34.
32. R v. Bodkin Adams  Criminal Law Review 365.
34. Kennedy, I, Grubb, A.Medical Law: Text with Materials (2nd ed.). Oxford: Oxford University Press; 1994:1205.
35. Re A (Children) (Conjoined Twins: Surgical Separation)  FCR 577.
41. R v. Woollin  AC 82.
42. R v. Matthews and Alleyne  2 Criminal Appeal Reports 30.
43. R (on the application of Pretty) v. DPP  1 AC 800.
45. Pattinson, S.Medical Law and Ethics. London: Sweet and Maxwell; 2009:18.
46. See note 34, Kennedy, Grubb 1994:1206.
47. See the discussion in Norrie, A.Between orthodox subjectivism and moral contextualism: Intention and the consultation paper. Criminal Law Review 2006;468–561.
48. Finnis, J. Intention and side-effects. In: Frey, RG.Liability and Responsibility. Oxford: Oxford University Press; 1991:32, 42, 43.
49. See note 48, Finnis 1991:41.
50. Simester, A, Chan, W.Intention thus far. Criminal Law Review 1997:704–16.
51. See further the discussions in McMahan, M.Revising the doctrine of double effect. Journal of Applied Philosophy 1994;11(2):317–21.
52. Beauchamp, T, Childress, J.Principles of Biomedical Ethics (5th ed). New York: Oxford University Press; 2001:128–32.
53. See note 26, Keown 2002:20.
54. See note 14, Kaczor 1998;297–317.
55. Huxtable, R.Get out of jail free? The doctrine of double effect in English law. Palliative Medicine 2004;18:62–8.
56. Randall, F, Downie, R.The Philosophy of Palliative Care. Oxford: Oxford University Press; 2006:114.