In March 2024, Daniel Kahneman – the man who did perhaps more than anyone else to shape the field of behavioural public policy – died. He is among a small handful of scholars who have had a huge effect on my own career, and in this essay – the first in a series of essays in a special section of the Journal that honour him – I reflect on how his work inspired much of my own.

The heart of prospect theory is the value function, proposing that the carriers of value are positive or negative changes from a reference point. Daniel Kahneman observed that if prospect theory had a flag, the value function would be drawn on it. The function is nonlinear, reflecting diminishing sensitivity to magnitude. When describing how human lives are valued, the function exposes profound incoherence. An individual life is highly valued and thus vigorously protected if it is the only life at risk. But that life loses its value when it is one of many endangered by a larger tragedy. Beyond this insensitivity, the function may actually decline when many lives at risk become mere numbers. The more who die, the less we care. Implications of this deadly ‘arithmetic of compassion’ for understanding and managing the risk from nuclear weapons are briefly discussed.

Kahneman and Tversky’s ‘Prospect Theory’ paper famously demolishes expected utility theory as a predictive device. However, it presents deviations from that theory as ‘normatively unacceptable’ and argues that decision-makers would normally correct them when possible. In a later paper, Kahneman rejects a similar argument (the ‘discovered preference’ hypothesis) advanced by Plott. Later still, Kahneman endorses Sunstein and Thaler’s ‘libertarian paternalism’, which aims to help people avoid deviating from their ‘true’ preferences. I report an email correspondence between Kahneman and me in which we debated whether his position on libertarian paternalism was consistent with his critique of Plott’s hypothesis.

Many moral judgments are rooted in the outrage heuristic. In making such judgments about certain personal injury cases, people’s judgments are both predictable and widely shared. With respect to outrage (on a bounded scale of one to six) and punitive intent (also on a bounded scale of one to six), the judgments of one group of six people, or 12 people, nicely predict the judgements of other groups of six people, or 12 people. Moreover, outrage judgments are highly predictive of punitive intentions. Because of their use of the outrage heuristic, people are intuitive retributivists. People care about deterrence, but they do not think in terms of optimal deterrence. Because outrage is category-specific, those who use the outrage heuristic are likely to produce patterns that they would themselves reject, if only they were to see them. Because people are intuitive retributivists, they reject some of the most common and central understandings in economic and utilitarian theory. To the extent that a system of criminal justice depends on the moral psychology of ordinary people, it is likely to operate on the basis of the outrage heuristic and will, from the utilitarian point of view, end up making serious and systematic errors.

This paper examines Daniel Kahneman’s concept of experienced utility and its roots in Bentham’s hedonic utilitarianism. It focuses on Kahneman’s call for a ‘separate value judgement’ to determine when experienced utility can be used to evaluate temporally extended outcomes (TEOs). Two potential judgements are proposed: comprehensiveness and personal independence. Comprehensiveness means that the measurement of utility captures all relevant aspects of instant utility. Personal independence means that the TEO is fully independent of other TEOs with which it might be combined (or ‘concatenated’). I argue that identifying TEOs meeting these criteria may be challenging, possibly restricting the applicability of experienced utility. I conclude by considering the implications for behavioural science’s quest for an unambiguous, measurable operationalisation of utility.

Daniel Kahneman’s legacy is best understood in light of developments in economic theory in the early-mid-20th century, when economists were eager to put utility functions on a firm mathematical foundation. The axiomatic system that provided this foundation was not originally intended to be normative in a prescriptive sense but later came to be seen that way. Kahneman took the axioms seriously, tested them for descriptive accuracy, and found them wanting. He did not view the axioms as necessarily prescriptive. Nevertheless, in the research program he conceived, factual discoveries about real decision-making were stated as deviations from the axioms and thus deemed ‘errors’. This was an unfortunate turn that needs to be corrected for the psychological enrichment of economics to proceed in a productive direction.

While in his early years, Kahneman followed the world of classic utilitarianism in which smart individuals base decisions on how they will truly feel each moment in the future, Kahneman in Mandel (2018) adopted a very different position, namely that what matters is the story people tell of their lives. He thus grappled with evolving stories of both the future and the past, and the presence of different decision-supporting evaluations for the short-run and the long-run.

Kahneman’s criticism of neoclassical rationality was central to his research programme. He argued that rationality understood as temporal consistency among preferences and beliefs is inapt as a descriptive and prescriptive standard of decision-making. Descriptively, consistency ignores high decision costs and biases, such as framing effects. Prescriptively, it is problematic since it neglects the processual nature of choice and the crucial role of regret. Instead, Kahneman argued in favour of using reasonableness as a standard, though he did not fully develop the concept in his work.

Behavioural public policy (BPP) operates within one of four cultural models of public management, an illustration of an influential scheme set out by Christopher Hood. Even though BPP can be fatalist, individualist or egalitarian, so far it has been hierarchicalist. Hallsworth’s manifesto is largely an expression of this hierarchicalist form of public management, with all its limitations and contradictions. As the manifesto pays relatively little attention to decentralist and egalitarian approaches, it misses a radical opportunity. Future work on BPP could incorporate entrepreneurial and egalitarian possibilities while recognising the difficulties of moving away from hierarchalism completely. Even though Hood cautions against a ‘public management for all seasons’, it remains a plausible path for the next generation of researchers and practitioners of BPP.

This article serves as a commentary on Michael Hallsworth’s 2023 piece, ‘A manifesto for applying behavioural science,’ featured in Nature Human Behaviour. The manifesto was prompted by methodological, practical and normative critiques directed at behavioural science and its role in public policy. In this commentary, I argue that the manifesto presents numerous insightful and constructive reform proposals regarding the scope, methods and values in behavioural science, which can help advance the field of behavioural public policy. While there is much to agree with, I contend in this commentary that applied behavioural science can and should delve deeper into the study of socially and culturally embedded processes of goal formation. Additionally, it should explore the institutional conditions necessary for individuals to formulate their goals competently and in a self-determined manner.

Viewed from the perspective of public policy, behavioural public policy (BPP) faces challenges in four main areas: Systems, Impatience, Nudging, and Scaling. To address these challenges, several suggestions are proposed. First, understanding how BPP interventions unfold in complex systems requires better diagnostics and the development of predictive and generative models of human behaviour. Second, the rapid pace of policy processes necessitates a shift towards generating timely and fit-for-purpose evidence. Third, maximising the opportunities presented by BPP, beyond merely ‘nudging’, demands the early and proactive application of behavioural science in the policy cycle. Fourth, achieving widespread impact in BPP initiatives means considering scale-up from the start. Lastly, the consistent and comprehensive integration of behavioural science into standard policymaking practices would support sustainable progress in addressing these challenges.

I’m grateful to the authors for taking the time to read and respond to the manifesto. I have great respect for the contributions each of them has made to our field, and I’d like to offer some clarifications and reflections prompted by their thoughts.

People buy some goods that they do not enjoy and wish did not exist. They might even be willing to pay a great deal for such goods, whether the currency involves time, commitment or money. One reason involves signaling to others; so long as the good exists, nonconsumption might give an unwanted signal to friends or colleagues. Another reason involves self-signaling; so long as the good exists, nonconsumption might give an unwanted signal to an agent about himself or herself. Yet another reason involves a combination of network effects and status competition; nonconsumption might deprive people of the benefits of participating in a network and thus cause them to lose relative position. With respect to real-world goods (including activities) of this kind, there is typically heterogeneity in relevant populations, with some people deriving positive utility from goods to which other people are indifferent, or which other people deplore. Efforts to measure people’s willingness to pay for goods of this kind will suggest a welfare gain, and possibly a substantial one, even though the existence of such goods produces a welfare loss, and possibly a substantial one. Collective action, private or public, is necessary to eliminate goods that people consume but wish did not exist. Legal responses here might be contemplated when someone successfully maneuvers people into a situation in which they are incentivized to act against their interests, by consuming a product or engaging in an activity they do not enjoy, in order to avoid offering an unwanted signal. Prohibitions on waiving certain rights might be justified in this way; some restrictions on uses of social media, especially by young people, might be similarly justified.

Some products, notably but not only platforms, increase in value for users as the number of other users increases. These interaction or network effects can result in ‘product market traps’ (Bursztyn et al., 2023) where people who use the product would be better off if they all stopped using it and switched to another product, but cannot because of coordination problems. A parallel but overlooked phenomenon is the labor market trap, where employees would be better off if they collectively left an employer, job, or profession, but cannot because of the difficulty of coordination. Product market and labor market traps pose a challenge to public policy because of the complexity of people’s behavior in networks, but can be mitigated in some cases with relatively simple taxes and regulatory interventions.

Local public managers increasingly use behavioral policy instruments to influence the behavior of citizens. However, despite their increased reliance on these instruments, there is little evidence on why local public manager would prefer behavioral instruments over classic stick, carrot or sermon-type instruments. We conduct a mixed-methods study, combining a stated-preference survey and two focus groups, to examine whether senior local public managers (directors and deputy directors) in Flanders prefer behavioral policy instruments over classic stick, carrot and sermon-type instruments, and explore whether their trust in citizens (perceptions of citizen’s ability, benevolence and integrity) affects these preferences for policy instruments. The results indicate that in some policy areas, such as health, public nuisance and road safety, public managers appear more willing to use behavioral policy instruments than classic sticks and carrots, but not sermons. Furthermore, we find that public managers’ trust in citizens does not appear to significantly affect their preferences for policy instruments, but that political and economic motives do play a role in their preferences for behavioral policy instruments. Finally, the results also indicate that the simultaneous use of behavioral and classic policy instruments (packaging) can help mediate the perceived risks of citizens’ non-compliance with behavioral policy instruments.

Recently, defaults have become celebrated as a low-cost and easy-to-implement nudge for promoting positive outcomes, both at an individual and societal level. In the present research, we conducted a large-scale field experiment (N = 32,508) in an educational context to test the effectiveness of a default intervention in promoting participation in a potentially beneficial achievement test. We found that a default manipulation increased the rate at which high school students registered to take the test but failed to produce a significant change in students’ actual rate of test-taking. These results join past literature documenting robust effects of default framings on initial choice but marked variability in the extent to which those choices ultimately translate to real-world outcomes. We suggest that this variability is attributable to differences in choice-to-outcome pathways – the extent to which the initial choice is causally determinative of the outcome.

This randomised online experiment aimed to investigate how eco-labelling and social nudging influenced sustainable food choice, as well as consider the effect of motivation to act sustainably. Participants were UK adults ≥18 years (n = 1399). Participants were asked to choose a hypothetical meal (beef, chicken or vegetarian burrito) and were randomly allocated to one of three conditions varying in labelling: eco-labelling; social nudge or control (no label). Co-primary outcomes were the frequency that the vegetarian and chicken burritos were chosen (i.e., the more sustainable food choices). There was evidence that more vegetarian (OR = 3.3 [95% CI 2.0, 5.3]) and chicken (OR = 2.5 [95% CI 1.8, 3.4]) burrito choices were made in the eco-label condition, over the beef burrito, compared to the control condition. In the social nudge condition, there was evidence that participants chose a vegetarian burrito over a beef burrito (OR = 1.7 [95% CI 1.1, 2.7]), but not a vegetarian burrito over a chicken burrito (OR = 1.4 [95% CI 0.9, 2.2]). Although both labels were effective at promoting participants to make more sustainable food choices, the eco-label was the most effective. Choice of burrito was modified by motivation to act sustainably across all conditions. This study suggests that future policy could include eco-labelling and/or a social nudge to reduce meat consumption and meet global climate change targets.

Commercial practices such as drip pricing, reference pricing and best-price guarantee can be used to set higher prices and mislead consumers, but protective measures can restore efficiency. In a placebo-controlled market experiment, we examined a treatment allowing for the use and misuse of commercial practices. Three additional treatments tested the effects of formal sanctions, informal sanctions and a regret nudge. We found that commercial practices led to higher prices, cheating was systematic and regret nudging was ineffective. Furthermore, formal and informal sanctions reduced both the likelihood of using commercial practices and the likelihood of cheating, leading to welfare increases.

The serial rapist model claims that a small number of intentional, repeat offenders are responsible for the majority of sexual assaults on college campuses. The model has formed the dominant argument for some of the most popular forms of campus intervention programs and is cited by high profile advocates and policymakers. Despite enthusiasm for the serial rapist model, it is not empirically well-supported and is contradicted by recent robust data. In this article, we ask: why does the serial rapist model have such broad and enduring appeal? In two US-based samples, one convenience and one representative, we find that people’s endorsement of the serial rapist model correlates with worldviews that cohere around ideas of a just and good status quo, and a preference for simple stories. Specifically, we find a positive relationship between endorsement of the serial rapist model and belief in a just world, system justification, social dominance orientation, need for closure and essentialism.