We explore whether there is a plausible probabilistic version of the Doctrine of Double Effect (DDE), and more generally pursue the question of how probabilistic outcomes affect the application of moral principles. Many think that the DDE helps explain why it is permissible to shunt a trolley onto a sidetrack to which one person is tied (thereby resulting in his death) in order to save the lives of five people tied to the main track, whereas it is impermissible to lead an unsuspecting person onto the main track in order to save the five. But we can ask: Does it make a difference if we have an option to lead a person onto the main track when there is only a small to moderate chance that he will be killed? Here we make a start toward an answer by investigating why it is generally wrong to risk harm to others, taking as a defeasible starting point a pluralistic deontological account of morality. In the process, we explore whether imposing risk is causing harm, how to sort permissible from impermissible risk impositions, and why we should not expect a linear function between degree of risk imposed and seriousness of wrong.

Trolley dilemmas were first developed by moral philosophers engaged in reflection on the ethics of permissible harm. But they have since become central to psychological research into morality. One reason why psychologists have paid so much attention to trolley dilemmas is that they see them as a key way to investigating the contrast between deontological and utilitarian approaches to ethics. This framing, however, departs from the original philosophical purpose of trolley dilemmas, and can lead psychological research astray. In this chapter, we question the assumption that trolley dilemmas can shed general light about the psychological bases of utilitarian decision-making. Some lay responses to trolley dilemmas that psychologists routinely classify as "utilitarian" in fact have little meaningful relation to what philosophers mean by this term. Even when what underlies lay responses to trolley dilemmas partly echoes aspects of a utilitarian approach to ethics, this doesn’t generalize to other moral domains, and tells us little about the psychological roots of other aspects of utilitarianism. Properly used, trolley dilemmas have a useful role to play in psychological research. But once we get clear about what we can, and cannot, learn from them, the current centrality of the trolley paradigm in moral psychology will seem overblown.

This chapter defends a non-consequentialist approach to justifying harming innocent nonthreatening people. The discussion centers on variations of cases where either a trolley driver or a bystander may redirect a trolley so that it kills one person, rather than five people towards whom it is headed. The article begins by critically examining other non-consequentialist proposals for why turning the trolley may be justified in both types of cases. It then defends seven principles, which together comprise the “Doctrine of Productive Purity” (DPP). The DPP implies that interpersonal harms may be justified by what produces them as opposed to by the goods they produce as in consequentialist views. The article contrasts the DPP with threshold deontology and considers how those whom one might permissibly harm may still permissibly resist such harm. The chapter concludes by considering limits of the DPP, the moral significance of the DPP for relations between people, and a new trolley problem that has implications for the killing/letting die distinction.

This chapter discusses three philosophical disputes concerning the comparison between the ethics of crashing autonomous vehicles and the Trolley Problem. The first dispute concerns whether there is something ethically problematic – or perhaps even flippant – about comparing the real-world issue of what autonomous vehicles should do in accident scenarios with the philosophy of the Trolley Problem. The second dispute concerns whether or not there is a close enough analogy between real-world accidents involving autonomous vehicles and the so-called trolley cases discussed in relation to the Trolley Problem. The third dispute concerns whether or not the large literature on the Trolley Problem discusses topics directly relevant to the real-world ethics of crashes with autonomous vehicles. The chapter considers key arguments on each side of the dispute. It also offers a diagnosis regarding whether the Trolley Problem is relevant for the ethics of autonomous vehicles. The conclusion is that it is either directly or indirectly relevant: It may be directly relevant because the Trolley Problem can teach us important lessons or indirectly relevant because identifying key differences between the ethics of autonomous vehicles and the Trolley Problem allows us to get clear on what matters most in the real-world ethics of autonomous vehicles.

This introduction explains the nature and interest of the trolley problem since its introduction to the philosophical literature, followed by a chapter by chaptersummary of the individual contributions to the volume.

This chapter puts forward a novel healthcare application of the Trolley Problem by applying it to our most recent global health crisis, the COVID-19 pandemic. The following hypothesis is introduced, analyzed and ultimately rejected: that the Trolley Problem can be used to distinguish between the supposed ethical permissibility of lifting lockdowns and the supposed ethical impermissibility of pursuing herd immunity during the COVID-19 pandemic. The aim of the chapter is twofold: both to test whether and how far we can progress within pandemic ethics by using the Trolley Problem and also to test whether the particular case of the COVID-19 pandemic can make a methodological contribution to trolley debates in philosophy.

This article addresses frequently asked questions about “trolleyology,” scientific research using trolley dilemmas to probe the moral mind:What are trolley dilemmas? What is the Trolley Problem? Why should philosophers or scientists care about the Trolley Problem? What have we learned from scientific research using trolley dilemmas? Do trolley dilemmas help us understand utilitarianism or other moral philosophies? Do hypothetical trolley judgments predict real judgments? Does it matter if they don’t? What about the relationship between the scientific (descriptive) Trolley Problem and the philosophical (normative) Trolley Problem? Can science really tell us anything about what’s right or wrong? What’s new in Trolleyology these days? Do you have any concluding thoughts?

Philippa Foot offered her original Trolley Case, where a driver will unavoidably kill either five or one, neither to present a moral quandary nor to pose any special problem for moral theory. Its purpose was simply to illustrate how her theory of duties – which she deployed to defend non-consequentialist intuitions about various other cases of harmful agency – could also handle cases like this one where consequentialist verdicts seem apt. The Trolley Problem arose when Judith Jarvis Thomson modified the case, using the bystander variation to raise difficulties for Foot. Intuitively, it seems that the bystander may equally turn the trolley, but that would amount to killing one to save five, which was ruled out by Foot’s theory (even though it allowed a driver to kill one to avoid killing five). That was the Trolley Problem, which amounted to a challenge to explain why the bystander trolley case is an exception to the usual prohibition against killing some to save others for the greater good. For decades Thomson saw it as a legitimate challenge and offered plausible ways of meeting it. Later, however, she changed her mind, concluding that it is not permissible for the bystander to turn the trolley after all. In this chapter, I begin by examining the relevant background, refining the understanding of the Trolley Problem, and considering basic methodological issues in this area of normative ethics. I then develop a solution to the Trolley Problem along with a diagnosis of what went wrong in Thomson’s later attempt to show that there was never really a Trolley Problem to begin with. In the end I hope to have shown why there was indeed an important theoretical challenge posed by the Trolley Problem and how it can be resolved in a principled way with minor revisions to Foot’s original theory.

Helen Frowe argues against a common view of the standard Trolley Scenario according to which it is permissible but not required to kill the one as a side effect of saving the five. She argues that saving the five and killing the one is morally required in that scenario. I defend the intuitive verdict that it is permitted but not required to turn the trolley in the Trolley Scenario. First, I show that the crucial premise of Frowe’s argument – the premise that one has a duty to prevent harm to others when one can do so without violating anyone’s rights, and without bearing an unreasonable cost – is false. And second, I present an independent argument (one originally offered by Frances Kamm) for the permissibility of not turning the trolley in the Trolley Scenario.

The Trolley Problem is not only one of the most widely discussed puzzles in moral philosophy. It is also one of the most controversial with respect to its perceived importance. At the one end of the spectrum there are those who consider it to reveal facts that belong at the very center of our moral understanding. At the other end of the spectrum there are those who consider it to be an example of contemporary philosophy at its most pointless. In this chapter, I critically address this dispute by tracing the discussion of the problem from its earliest formulation on the work of Philippa Foot, Judith Thomson, and Frances Kamm. Then I discuss a number of the most important criticisms of these discussions, drawing on the work of Barbara Fried. In doing so, I describe not only the actual causes of the problem’s continuing interest but also the underlying justification and rationale for that interest to which that history gives evidence.

This chapter explores the relationship between the Trolley Problem and the distinction between doing and allowing harm. I begin by discussing the origin of the Trolley Problem, considering Philippa Foot’s original version of the case and what Judith Jarvis Thomson’s modification of the cases shows. Thomson’s original (and best) argument presents the bystander trolley case not to undermine the distinction between doing and allowing harm, but to raise questions about precisely what we mean when we say this distinction matters morally. I then consider whether the Trolley Problem challenges the moral relevance of doing/allowing distinction. I show that the trolley case is not a straightforward counterexample to the doing/allowing distinction. But does the Trolley Problem show that the defender of the doing/allowing distinction cannot give a consistent and intuitively acceptable answer to how much harder doing harm is to justify than merely allowing harm? I argue that this concern is misguided. We should expect there to be other morally relevant features that interact with the doing/allowing distinction, strengthening or weakening constraints against doing harm. Consideration of the Trolley Problem shows that both the distinction between doing and allowing harm and a sister deontological distinction are needed.

Since the publication of Judith Thomson’s 1976 paper, solving the Trolley Problem has been a favorite preoccupation of utilitarians and deontologists. Why is it permissible to divert a runaway trolley, thereby killing one person to save five others, but impermissible to push a big man onto a track to save five others.To date, virtue ethicists have not shown any interest in the debate.An obvious reason for this lack of interest is that virtue ethicists reject the very idea that there are universal moral rules and principles, according to which actions can be evaluated as permissible or impermissible. It is possible to frame the Trolley Problem in terms of what a virtuous person would and wouldn’t do, but then a further problem emerges, namely, that trolley experiments are not good tests of character. They rule out many of the ways that virtuous people can distinguish themselves from the non-virtuous.I discuss some of these problems in the first part of the chapter. In the second part, and with a few reservations and qualifications in mind, I argue that a virtue ethicist can support our commonsense intuitions in two central cases – Bystander and Footbridge – while also offering a response to Thomson’s Loop challenge.

In Chapter 7, I argue that the solidarity rationale for the PDE from Chapter 3 enables a response to Joshua Greene’s argument that findings from empirical psychology debunk deontological constraints on causing harm. Greene’s deontological debunking argument is based on the dual-process theory of moral judgment, and I begin by reviewing the main elements of this theory. Next, I describe the two stages of Greene’s debunking argument. Stage 1 aims to debunk the case-based intuitions that seem to support deontology over consequentialism, while Stage 2 aims to debunk deontological normative ethics. I argue that Stage 2 of Greene’s argument is unsatisfactory, and I explain why it fails to undermine the solidarity rationale for the PDE. Finally, I outline two possible explanations of why our case-based intuitions should be sensitive (even if imperfectly) to a feature of conduct – intentional harm – that is morally significant.