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Double Effect, Triple Effect and the Trolley Problem: Squaring the Circle in Looping Cases

Published online by Cambridge University Press:  01 March 2008

University College


In the Trolley Case (Figure 1), as devised by Philippa Foot and modified by Judith Jarvis Thomson, a runaway trolley (i.e. tram) is headed down a main track and will hit and kill five unless you divert it onto a side track, where it will hit and kill one.

Research Article
Copyright © Cambridge University Press 2008

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1 See Foot, Philippa, ‘The Problem of Abortion and the Doctrine of the Double Effect’, Oxford Review, no. 5 (1967), pp. 515Google Scholar, and Thomson, Judith Jarvis, ‘The Trolley Problem’, The Yale Law Journal 94 (1985), pp. 13951415.CrossRefGoogle Scholar

2 About 77 per cent of the 14,000 people who took an online BBC poll said that one should divert in this case. About 90 per cent of the respondents to Marc Hauser's online Moral Sense Test indicated that it was permissible to divert in this case. See ! and ! Hauser, Marc, Moral Minds (New York, 2006), p. 128.Google Scholar

3 All such references are to Intricate Ethics.

4 This is a slight variation on a case of Thomson's in which the person on the bridge is toppled by a wobbling of the bridge's handrail. Thomson also entertains a version of the case in which you shove the one off the bridge with your bare hands. (See Thomson, ‘The Trolley Problem’, pp. 1409–10.) About 90 per cent of respondents to Marc Hauser's online Moral Sense Test deemed such shoving impermissible. (See Hauser, Moral Minds, p. 128.)

5 It also prohibits the intending of evil as an end in itself.

6 The Doctrine of Double Effect does not permit any evil that is merely foreseen. More would need to be said in order to vindicate the claim that the merely foreseen killing of the one in the Trolley Case is permitted by this doctrine. One would need, for example, to establish that the foreseen harm is not out of proportion to the good that the agent realizes.

7 See Thomson, ‘The Trolley Problem’, pp. 1402–3. Given Thomson's configuration of the tracks in her Loop Case, not only would the five inevitably be hit by the trolley if the one were not present, but the one would inevitably be hit by a trolley if the five were not present. In the absence of the five, the trolley would loop around and hit and kill the one from behind. Michael Costa has argued that the permissibility of turning the trolley onto the one in Thomson's Loop Case is partially explained by the fact that the one is so-protected by the five. (See Michael, Costa, ‘Another Trip on the Trolley’, The Southern Journal of Philosophy 24 (1987), pp. 437–49.Google Scholar) We should stipulate, therefore, that in the absence of the five, the trolley would carry on harmlessly down the straight main track past the point at which the looping track reconverges with the main track rather than turning onto that looping track and hitting and killing the one from behind. (See Figure 3, and cf. Kamm's semi-permeable wall on p. 122 n. 4.)

8 Thomson, ‘The Trolley Problem’, p. 1403.

9 Or at least this is how it strikes most moral philosophers who have expressed their views in print (or to me in person). Interestingly, however, respondents to Marc Hauser's online Moral Sense Test split roughly 50–50 regarding the permissibility of diversion in a case that is modelled on Thomson's Loop Case. (See Hauser, Moral Minds, pp. 128–9.)

10 See Thomson, ‘The Trolley Problem’, p. 1403.

11 Thomson offers further reasons for abandoning the Doctrine of Double Effect in her ‘Self-Defense’, Philosophy and Public Affairs 20 (1991), pp. 283–310.

12 Kamm informs us on p. 129, n. 55, that this apt name is due to Thomas Hurka. Kamm does not offer an unqualified endorsement of the Doctrine of Triple Effect, as she raises a number of problems for it on pp. 132–8. These problems do not bear on the cases under discussion in this article.

13 See p. 92. This distinction will be explained and illustrated in the main text below.

14 See pp. 118 and 136–7.

15 I would say the same thing about Kamm's Wagon Case in which, if the trolley is diverted onto the looping side track, it comes to a halt but depresses a button that starts up a wagon on that same track that proceeds to head towards the five yet is stopped before it gets to the five because it hits the one (see p. 94). When we abstract from the fact that the wagon will come to a halt by hitting the one, here, as in the Loop Case, you do not eliminate or lessen the threat that the trolley poses to the five by diverting it, even though in this case the trolley poses its equally grave threat by causing the wagon to start up.

16 Similarly, in Kamm's Party Case described above, you do not throw the party in order to get your guests to clean up afterwards, since one does not do something in order to mitigate the bad consequences of the doing of that very thing.

17 One might insist that your primary goal is really to minimize the number of people who will be killed rather than to save the five on the main track. Moreover, it is arguable that you hit the one in order to, rather than merely because you will thereby, minimize the number of people who are killed. My reply to this challenge is that your primary goal need not be that of minimizing the number who will be killed. Rather, your primary goal might be that of saving the five who are imperilled by the trolley, where this goal is constrained in so far as you would abandon it if there were grounds sufficient to condemn what you would need to do in order to save the five. If you are a non-consequentialist, such grounds will not be exhausted by considerations of numbers alone. For if they were, then you would not hesitate to kill the one in the Bridge Case.

18 This aspect of the case is inspired by Kamm. See p. 124 n. 9.

19 This aspect of the case is inspired by the following case of Derek Parfit's that he has presented in correspondence. You can divert the trolley onto a track that loops around and back towards the five from the other direction just as in Thomson's Loop Case which I describe in the main text above. But, unlike Thomson's version, there is not already someone stuck on the looping track. Rather, as the trolley travels down the looping track it hits and depresses a lever, which causes someone to fall from a bridge and onto the looping track in front of the train, thereby causing the train to come to a halt by hitting that person. The novelty of Parfit's case that I exploit is that the movement of the already diverted trolley is among the causes of the person's falling from the bridge. Parfit reports that Kamm has affirmed the permissibility of such diversion in conversation.

20 Kamm, F. M., Morality, Mortality, vol. 2 (New York, 1996), p. 163.Google Scholar She immediately goes on to write that ‘this helps us see that redirection [of the threat such as a trolley] is not morally crucial to redirection cases’ (Morality, Mortality, vol. 2, p. 163). One might try to distinguish morally both the original Trolley Case and the Lazy Susan Case from the famous Transplant Case (where the only way to save five from vital organ failure is to carve up a healthy individual and transplant his organs into the five) by noting that both the Trolley Case and the Lazy Susan Case involve the redistribution (≠ redirection) of a threat by making it the case that the trolley that threatens the five now threatens the one. The carving up of the one in the Transplant Case, by contrast, is not a redistribution to the one of that which threatens the five. Perhaps you may kill one when this is necessary to save five just in case this killing is by means of the redistribution to the one of that which threatens the five. The problem with this suggestion is that it doesn't account for the impermissibility of toppling the one in the Bridge Case, as in this case the threat that the trolley poses is redistributed (though not redirected) from the five to the one.

21 Similar worries crop up in the literature on the Doctrine of Double Effect: e.g., ‘He did not intend the killing of the one but merely that he be blown to bits’, or ‘In bombing this village, he did not intend the death of innocent civilians, but merely the realistic appearance of massive casualties’. It is an open question whether a moral principle that does not place any moral significance on one's actual state of mind could do a better job than the Doctrine of Triple Effect of distinguishing looping cases from the Bridge Case. On pp. 156–8, Kamm attempts to translate the state-of-mind talk involving intention, etc., of the Doctrine of Triple Effect into the non-state-of-mind vocabulary of the principles of permissible harming that she develops in that chapter. It is not clear to me, however, how such non-state-of-mind principles would categorize and distinguish the range of looping cases under discussion in this article.

22 Thomson, ‘The Trolley Problem’, p. 1403.

23 Both the Ramp Case and the description of the manner in which it differs from the Bridge Case are due to John Martin Fischer. See his ‘Thoughts on the Trolley Problem’, Ethics: Problems and Principles, ed. John Fischer and Mark Ravizza (Fort Worth, Tx., 1992), pp. 308–17, at pp. 315–16.

24 This is, of course, a rhetorical question. I concur with Fischer that ‘whether the train is shunted to the right or upward cannot be morally significant’ (Fischer, ‘Thoughts on the Trolley Problem’, p. 316).

25 Might others succeed where Kamm has failed to distinguish the Bridge Case (and others like it) from looping cases? I very much doubt it, as I suspect that Kamm's writings on the trolley problem over the years have either refuted any such published attempt or provided the resources with which to construct a refutation.

26 See Hauser, Moral Minds, pp. 128–9.

27 See Warren, Quinn, ‘Actions, Intentions, and Consequences: The Doctrine of Double Effect’, Philosophy and Public Affairs 18 (1989), pp. 334–51.Google Scholar