Aquinas on Defensive Killing: A Case of Double Effect?

The Thomist 69 (2005): 341-70 AQUINAS ON DEFENSIVE KILLING: A CASE OF DOUBLE EFFECT? GREGORY M. REICHBERG International Peace Research Institute, Oslo (PRIO) Oslo, Norway THENOW-STANDARDREADINGofAquinas'saccountof private self-defense in STh 11-11, q. 64, a. 7 holds that it precludes any kind of deliberate killing. Defensive action that causes the death of an assailant will be morally permissible only when this lethal outcome has the character of a pure side effect. Hence, when Aquinas asserts that in self-defense "the killing of the attacker" is "beyond the intention" (praeter intentionem) of the defender, he is taken to be formally denying that a private defender can justifiablychoose (however reluctantly) to kill his assailant in order to protect himself from grave harm. Article 7 is thus said to exemplify what has since come to be called 'the principle of double effect' (PDE). 'Double effect' is the heading under which the ethical quandaries surrounding side-effect harm have traditionally been discussed in philosophy. This term is shorthand for the two different kinds of effects that can emerge from our actions. On the one hand, there is the very state of affairs that our actions are meant to produce. This goal we will succeed at achieving more or less well, depending on our skill. On the other hand, there are the side effects that result from this deliberate intervention in the world. The idea that we are answerable for these side effects, yet in a manner different from the way we are accountable for our intentional projects, has been dubbed the 'principle of double effect' (PDE). This principle holds that while we can never be justified in deliberately willing a wrong, we may sometimes have 341 342 GREGORY M. REICHBERG moral warrant for allowing harmful side effects to eventuate from our otherwise good actions.1 My argument here is that Aquinas did not in fact appeal to a version of PDE in formulating his theory of justifiable defensive killing in STh II-II, q. 64, a. 7. The broader context of his other statements on the morality of participation in violence, as well as the twelfth- and thirteenth-century canon-law teaching on this topic, indicate that he did not take self-defense to be an act from which harmful side effects (including the death of the assailant) might flow. He viewed self-defense instead as an aim that might justify the application of proportionate force against an assailant, even to the point of deliberately causing his death, if this were the only effective measure available at the time. Aquinas recognized that lethal force could also be applied with a very different purpose in mind, namely, to avenge a wrong. It was precisely by way of contrast with this latter aim that Aquinas described defensive killing as "praeter intentionem." I It is undeniable that the name PDE was originally taken from a sentence in the responsio to STh II-II, q. 64, a. 7 ("from the act of self-defense there follows a double effect"). Yet whether a doctrine of double effect may be found therein is a matter of some dispute. When Aquinas states that a private individual who engages in lethal self-defense must aim solely at preserving his own life, such that the death of his assailant would lie outside of his intention (praeter intentionem), does he mean to assert that an agent of this kind may never deliberately inflict death upon another as a means of saving himself? In other words, does this article restrict the scope of private self-defense to actions which, although they may foreseeably result in the attacker's death, can never be chosen precisely with that outcome in mind? 1 For further elucidations on PDE, see Gregory Reichberg and Henrik Syse, "The Idea of Double Effect-In War and Business," in L. Bomann Larsen and 0. Wiggen, eds., Responsibility inWorldBusiness: ManagingHarmful Side-effectsofCorporateActivity (Tokyo: United Nations University Press, 2004), 17-38. AQUINAS ON DEFENSIVE KILLING 343 Drawing on Cajetan's Summa commentary, Joseph Boyle has argued for an affirmative answer to this question.2 His argument is built around an analysis of the term praeter intentionem (as it is used in...