The book The Behavioral Code: The Hidden Ways the Law Makes Us Better or Worse asks: should the purpose of law be to create more public good ex-ante? If it is, is the law effective in achieving that? The authors offer definitive answers to both questions: yes, the purpose of law should be to improve public life by preventing unwanted harmful behavior and increasing pro-social behavior; and no, the law is not currently achieving that goal effectively. I recommend this book for every legal scholar with a desire to learn about the behavioral science of interaction with the law. I do, however, emphasize that we should proceed with caution, as both our understanding of causal inference and behavioral change are in the early stages.

The book successfully connects two kinds of literature: social science evidence regarding the law's effect on behavioral change, and behavioral science evidence on mechanisms related to pro-social behavior. The goal is to discover how law can incorporate new understandings of human behavior to achieve effective public policy that minimizes harm and maximizes benefit. The book is organized into 10 chapters that follow these broad themes: evidence on incentives in criminal and tort law (Chapters 2 and 3), the effects of persuasion (Chapter 4), the psychology of civil obedience (Chapter 5), nudging by reliance on norms (Chapter 6), and pitfalls: ignorance, limitations on compliance, and external incentives toward anti-social conduct (Chapters 7, 8, 9). The first and final chapters are dedicated to the argument of the book. All the evidence presented in the bulk of the book supports the authors' motivation for writing it: changing the very nature of how society thinks about the purpose of law from a responsive, reactionary social instrument to a proactive, preventive tool.

In Chapter 2, the authors tackle the big question of criminal law: does punishment deter crime? Or, using the language the book is advocating, is criminal law currently effective in preventing harmful behavior? “Rather than just assess whether punishment is fair or justified, we must ask whether and how punishment shapes behavior and reduces crime.” (p. 17). The authors argue for a narrow application of Beccaria's command: “Every punishment which does not arise from absolute necessity is tyrannical.” (p. 19) Necessity is behaviorally operationalized as effectiveness in reducing crime. The authors discuss a plethora of evidence from natural experiments and quasi-experiments that tell a sobering story. Currently, it is plausible that punishment does not have a net positive effect on society. Furthermore, the authors present convincing evidence that some forms of excessive punishment negatively impact society. The authors call for a cautious approach to punishment, wary of punitive intuitions (both the public's and politicians'). The chapter is imperative for any policy-minded reader.

Chapter 3 takes a similar approach toward torts: other than being restorative, can tort law reduce misconduct? Here, the authors reach a similar conclusion to Chapter 2, as “there is no conclusive evidence that tort helps to reduce misconduct and damaging behavior” (p. 52). Chapters 4, 5, and 6 turn from direct legal effectiveness evidence to the behavioral science of changing behavior. These chapters discuss possible mechanisms that the law can use to be more effective. Chapter 4 emphasizes the role of persuasion over “naive” incentives. People have strong moral values and norms that influence their behavioral choices. The authors argue that compliance with the law depends on congruence between legal rules and people's moral values. Chapter 5 is devoted to the question of how people develop different levels of civil obedience. The chapter details the destructive relationship between institutional misconduct of law enforcement agencies and rising civil disobedience. Procedural justice is discussed as a possible mitigating solution. In Chapter 6, the authors take a significant step forward in their argument. The law, they argue, cannot be effective as long as it takes the individual as its subject of interest. Legal effectiveness requires policy orientation, a perspective of group behavior.

Chapters 7, 8, and 9 take another turn, from behavioral tools the law can use to behavioral challenges the law must overcome to be effective. Chapter 7 discusses prevalent legal ignorance and socio-economic constraints on people's ability to comply with the law. Chapter 8 is devoted to trust in government, or the lack thereof, as a barrier for accepting policies that limit free choice. Finally, Chapter 9 discusses the role of corporate and organizational culture in negating legal effectiveness.

The book is comprehensive, but there is more to be done. Future work should also focus on the role of institutions such as administrative agencies, District Attorney offices, Courts, and local governments in affecting behavior and the role of politics on compliance with the law.

The book has a materialistic view of the law, “it is a stack of paper.” (p. 6). But the book also takes a clear normative stand on what the law should be: a set of policies that apply empirical evidence to affect behavior. In theory, this is a noble call for “law for the public good.” However, there are two caveats. The first is related to causal inference and the second to behavioral change and publication bias. The authors note throughout the book the difficulties of reaching causal conclusions from observational data and the replication crisis of social psychology experiments. From a causal inference perspective, measuring the causal effect of the law on behavior is notoriously complicated. With minimal options for controlled randomization, and due to the fundamentally reactionary nature of legal change (introducing issues of reverse causation, for example), there is a limit to what we can learn from quasi-experiments.

Second, if there is one thing behavioral scientists can agree on, it is that changing people's behavior is complex. Take, for example, The Behavior Change for Good Initiative, an unprecedented large-scale collaboration between academics and organizational partners conducting “mega-studies” to understand what affects behavior as a response to behavioral science failures of the past (Milkman et al., 2021). Add to that the notoriety of publication bias: selective underreporting of research, where only positive results are published widely, making conclusions exclusively based on published studies misleading (McShane et al., 2019). The most severe case of publication bias is the fabrication of results (which is more common than behavioral scientists like to admit) and p-hacking. Retraction of papers is common (see https://retractionwatch.com/). There is a long way to go before behavioral and social science can be trusted as the sole sources of legal legitimacy (there are positive developments, such as the Open Science Framework [OSF] and norms of pre-registration. Still, we are in the early days).

Despite the issues with the current state of behavioral science, I wholeheartedly support the book's goal. Although it is self-evident that law is at least partially tasked with responding to and incentivizing behavior, research on the underlying mechanisms that affect what I call “legal behavior” is currently dispersed and lacks organizing principles. This book is a step forward at changing that. Partly to blame is the legal field that resisted experiments (Lynch Holly et al., 2020) and does not systematically study behavior. This book should be required reading for every law student, and hopefully, in the future, the legal profession will embrace “behavioral thinking.”