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Foot and Trolley Cases: Kant Was Wrong

Can discoveries in moral psychology play a role in undermining, or supporting, ethical principles? Considering Foot (1967) suggests that at least some philosophers can make good use of discoveries in moral psychology within the kinds of argument they already offer.

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This is a strange place to being discussion of whether discoveries in moral psychology can play a role in undermining, or supporting, ethical principles. Most of the published debate about this issue is framed in terms of an opposition between moral psychologists and non-utilitarians (e.g. Singer, 2005, Königs, 2020;[1] one notable exception is Kumar & Campbell, 2012). One side argues that discoveries in moral psychology support utilitarians, the other that such discoveries are normatively insignificant. Although we will eventually consider these arguments, I wanted to start off the beaten track with an argument from Foot (1967) because it gives us a compatively simple route to a significant conclusion.

A second reason for starting with Foot is that not everyone taking the course need have studied ethics previously. Foot (1967) is one good place to start.

Foot’s Accidentally Famous Example

Foot (1967) is famous not for its central argument but as the source of trolley cases (Hacker-Wright, 2019). In fact Foot makes little use of the trolley scenario, which is introduced only as a refinement of examples that were already widely discussed.[2] But Foot’s argument is highly relevant to our concern with moral psychology’s ethical significance.

As we will see, if Foot’s broad approach is not entirely misguided, there is a role for discoveries in moral psychology in undermining, and supporting, ethical principles.

Foot’s Method of Trolley Cases

On ‘the general question of what we may and may not do where the interests of human beings conflict’ (p. 5), Foot (1967) argues against straightforward applications of the doctrine of double effect. To this end, she uses the method of trolley cases.

What is the method of trolley cases? It involves considering pairs of moral scenarios in which her readers are supposed to make apparently contradictory judgements. For instance:

‘We are about to give a patient who needs it to save his life a massive dose of a certain drug in short supply. There arrive, however, five other patients each of whom could be saved by one-fifth of that dose. We say with regret that we cannot spare our whole supply of the drug for a single patient [...]. We feel bound to let one man die rather than many if that is our only choice. Why then do we not feel justified in killing people in the interests of cancer research or to obtain, let us say, spare parts for grafting on to those who need them?’ (Foot, 1967, p. 13).

The idea is then to consider which principle (or principles[3]) might justify the pattern of judgements, thereby removing the apparent contradiction.

Foot argues against straightforward applications of the doctrine of double effect by producing further cases:

‘Suppose, for instance, that there are five patients in a hospital whose lives could be saved by the manufacture of a certain gas, but that this inevitably releases lethal fumes into the room of another patient whom for some reason we are unable to move. His death, being of no use to us, is clearly a side effect, and not directly intended. Why then is the case different from that of the scarce drug, if the point about that is that we foresaw but did not strictly intend the death of the single patient? Yet it surely is different’ (Foot, 1967, p. 17).

Foot concludes that it is not the doctrine of double effect but rather a contrast in the priority of duties not to harm over duties to help which explains the patterns of judgements in the pairs of moral scenarios she considers.[4] This conclusion is based on the consideration that invoking the priority of duties not to harm over duties to help can make patterns of judgement consistent in all the cases covered by the doctrine of double effect[5] and also in other cases in which that doctrine does not make the patterns of judgement consistent.

Foot’s Use of Moral Psychology

There are some signs that Foot’s argument relies on empirical claims in moral psychology. She describes herself as ‘trying to discern some of the currents that are pulling us back and forth’ (p. 10). This indicates that she treats the argument as depending on what actually explains why people make certain judgements.

Another sign is Foot’s appeals to legal requirements in defending her view that it would be wrong to use a gas to save five lives if doing so would be lethal for a fifth:

‘The relatives of the gassed patient would presumably be successful if they sued the hospital and the whole story came out’ (Foot, 1967, p. 17).

Finally, Foot makes claims about which factors determine ‘what we say in these cases‘:

‘My conclusion is that the distinction between direct and oblique intention plays only a quite subsidiary role in determining what we say in these cases, while the distinction between avoiding injury and bringing aid is very important indeed’ (Foot, 1967, p. 12, my emphasis).

If this is right, Foot depends on two kinds of empirical fact: facts about what people would judge when presented with particular scenarios, and facts about which factors determine why they make those judgements.

Foot’s argument therefore appears to be continuous with moral psychology. Of course she used guesswork rather than repeatable observation in attempting to get at the facts. There are some discoveries relevant to Foot’s argument which suggest that guesswork, although useful, may not be sufficient.

Which Discoveries Are Relevant to Foot’s Argument?

In pairs of moral scenarios like those which Foot considers, what factors might sway people’s judgements? Foot herself envisages that the judgements will be explained by moral principles (and that identifying which principles sway the judgements will provide support for the truth of those principles).

Waldmann, Nagel, & Wiegmann (2012, p. 288) offers a brief summary of some factors which have been considered to influence judgements including:

  • whether an agent is part of the danger (on the trolley) or a bystander;
  • whether an action involves forceful contact with a victim;
  • whether an action targets an object or the victim;
  • how far the agent is from the victim;[6] and
  • how the victim is described.

They comment:

‘A brief summary of the research of the past years is that it has been shown that almost all these confounding factors influence judgments, along with a number of others [...] it seems hopeless to look for the one and only explanation of moral intuitions in dilemmas. The research suggests that various moral and nonmoral factors interact in the generation of moral judgments about dilemmas’ (Waldmann et al., 2012, pp. 288, 290).

How, if at all, is this relevant to Foot’s argument?

Consequences of Moral Psychology

One possibility is to see the scientific discoveries about trolley cases as relevant but of little importance. One of Foot’s aims was to show that reflection on trolley cases did not provide strong justification for accepting the doctrine of double effect.[7] This conclusion is not undermined, and may be strengthened, by the scientific discoveries.

Another possibility is to see the scientific discoveries about trolley cases as undermining Foot’s argument. Foot appears to have argued like this:

  1. the distinction between avoiding injury and bringing aid plays a role in explaining people’s patterns of judgement in trolley cases; therefore:

  2. we should apply this distinction in making moral judgements about abortion.

Foot’s argument for the premise (1) is based on informal observation. Since the scientific discoveries imply that informal observation does not enable us to know the premise (1), they undermine her argument.

You might reasonably feel some tension here. Reading Foot (1967), it is hard not to feel compelled by her argument. And yet the findings summarised by Waldmann et al. (2012) (which we will consider in more detail later) reveal that this feeling may well be based on irrelevant factors.

This feeling of tension points us to a third possibility. Perhaps it is not just Foot’s argument that should be rejected. Perhaps the scientific discoveries show that Foot’s method of trolley cases is unreliable as it stands and should not be used without additional support. For Foot’s method of trolley cases relies on two assumptions:

  1. patterns of judgements about moral scenarios are determined by moral principles; and
  2. the fact that one principle has more influence than another principle in determining a pattern of judgements about moral scenarios is a reason (but perhaps not a decisive reason) to prefer the truth of the first principle over the truth of the second.[8]

If Waldmann et al. (2012, p. 290) are right that ‘various moral and nonmoral factors interact in the generation of moral judgments about dilemmas’, it seems that both claims require qualification and should not be accepted without further evidence or argument.

Note that none of these possibilities is incompatible with Foot’s broad approach, given that we can replace guesswork with repeatable observation. For all the considerations offered so far show, it may be possible to discovery morally-relevant differences between scenarios by observing people’s judgements, and these discoveries may provide reasons for preferring the truth of one moral principle over another.

The point is not that there is anything fundamentally wrong with Foot’s approach to doing ethics: it is that if we adopt this approach, then discoveries in moral psychology are directly relevant to philosophical arguments.


There is room for debate about how discoveries in moral psychology are relevant to Foot (1967)’s argument.

But Foot’s interest in why people are disposed, on reflection, to make certain patterns of judgements is clearly one that discoveries in moral psychology can advance and have advanced. Reliance on guessing is not an essential feature of her method.

For this reason, unless Foot’s broad approach is misguided, discoveries about moral psychology are relevant to ethics. They could play a role in undermining, or supporting, ethical principles.

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doctrine of double effect : ‘the thesis that it is sometimes permissible to bring about by oblique intention what one may not directly intend’ (Foot, 1967, p. 7).
trolley cases : Scenarios designed to elicit puzzling or informative patterns of judgement about how someone should act. Examples include Trolley, Transplant, and Drop. Their use was pioneered by Foot (1967) and Thomson (1976), who aimed to use them to understand ethical considerations around abortion and euthanasia.


Foot, P. (1967). The problem of abortion and the doctrine of the double effect. Oxford Review, 5, 5–15.
Hacker-Wright, J. (2019). Philippa Foot. In E. N. Zalta (Ed.), The Stanford Encyclopedia of Philosophy (Fall 2019). Metaphysics Research Lab, Stanford University.
Königs, P. (2020). Experimental ethics, intuitions, and morally irrelevant factors. Philosophical Studies, forthcoming, 1–19.
Kumar, V., & Campbell, R. (2012). On the normative significance of experimental moral psychology. Philosophical Psychology, 25(3), 311–330.
Nagel, J., & Waldmann, M. R. (2013). Deconfounding distance effects in judgments of moral obligation. Journal of Experimental Psychology: Learning, Memory, and Cognition, 39(1), 237.
Rini, R. A. (2016). Debunking debunking: A regress challenge for psychological threats to moral judgment. Philosophical Studies, 173(3), 675–697.
Singer, P. (2005). Ethics and Intuitions. The Journal of Ethics, 9(3), 331–352.
Thomson, J. J. (1976). Killing, Letting Die, and The Trolley Problem. The Monist, 59(2), 204–217.
Waldmann, M. R., Nagel, J., & Wiegmann, A. (2012). Moral Judgment. In K. J. Holyoak & R. G. Morrison (Eds.), The oxford handbook of thinking and reasoning (pp. 274–299). Oxford: Oxford University Press.


  1. See Singer (2005, p. 343): ‘A dominant theme in normative ethics for the past century or more has been the debate between those who support a systematic normative ethical theory—utilitarianism and other forms of consequentialism have been the leading contenders—and those who ground their normative ethics on [...] intuitions.’ ↩︎

  2. Compare Foot (1967, p. 10): ‘the controversy has raged around examples such as the following [...] a pilot whose aeroplane is about to crash is deciding whether to steer from a more to a less inhabited area. To make the parallel as close as possible it may rather be supposed that he is the driver of a runaway tram which he can only steer from one narrow track on to another.’ ↩︎

  3. See Foot (1967, p. 17): ‘I have not, of course, argued that there are no other principles.‘ ↩︎

  4. See Foot (1967, p. 12): ‘My conclusion is that the distinction between direct and oblique intention plays only a quite subsidiary role in determining what we say in these cases, while the distinction between avoiding injury and bringing aid is very important indeed.’ ↩︎

  5. See Foot (1967, p. 12): ‘the distinction of negative and positive duties explains why we see differently the action of the steering driver and that of the judge, of the doctors who withhold the scarce drug and those who obtain a body for medical purposes, of those who choose to rescue five men rather than one man from torture and those who are ready to torture the one man themselves in order to save five.’ ↩︎

  6. After this review was published, Nagel & Waldmann (2013) provided substantial evidence that distance may not be a factor influencing moral intuitions after all (the impression that it does was based on confounding distance with factors typically associated with distance such as group membership and efficacy of action). ↩︎

  7. Foot (1967, p. 14): ’even if we reject the doctrine of the double effect we are not forced to the conclusion that the size of the evil must always be our guide.’ ↩︎

  8. There are some obvious counterexamples to this assumption (for one thing, some otherwise plausible principle may not be reflected in a set of trolley cases at all). My formulation of the assumption surely requires qualifying. But this does not affect the argument. ↩︎