Recent developments give new urgency to questions about evidence. The rise of the internet, the widespread use of social media, the Covid-19 pandemic, the accelerating concern about climate change, the 2020 US presidential election, the assault on the United States Capitol on January 6, 2021, and the Trump administration generally are obvious examples of contemporary events in which controversies about facts and the evidence offered to prove them have taken center stage. More and more, the use and misuse of evidence has a prominence that would surprise anyone who thinks of evidence as a collection of often-silly lawyers’ rules governing the conduct of trials. But evidence is not only about trials and not only about law. It is about science; it is about history; it is about psychology; and it is, above all, about human rationality. What do we know, and how do we know it? More specifically, what do we know about the facts of the world, and how do we know them?
No one book can hope to deal with the subject of evidence in its full depth and complexity. But we cannot ignore the increasing importance of questions of evidence in public policy and personal decision making. And it would be a mistake to neglect what scientists, philosophers, historians, psychologists, and even lawyers can teach us about the questions of evidence that dominate the headlines, pervade public policy, and guide the decisions we make in our everyday lives. In this book I draw on these and other perspectives to make sense of the evidentiary dimensions of human decision making. Although I hope that this book will contribute to academic discussions of evidence by philosophers, lawyers, psychologists, and others, my principal goal is to illuminate for nonacademics as well as academics the role of evidence in politics, policy, and the countless other domains in which facts matter—and where getting the facts right matters even more.
This book was first inspired by news outlets’ increasing observations that this or that public official—usually, but not always, ex-president Trump (and his lawyers)—had made some statement or taken some action “without evidence.” The phenomenon was highlighted in the aftermath of the 2020 presidential election, when, in a televised speech on November 5, 2020, Trump claimed to have won the election. Only because of widespread fraud, he insisted, could anyone possibly conclude otherwise. Shortly thereafter, Republican senator Pat Toomey of Pennsylvania observed that there was “no evidence anyone has shown me of any widespread corruption or fraud” and that the president had “made very, very serious allegations without any evidence to support it.” Republican representative Adam Kinzinger of Illinois echoed that thought, insisting that “[if there are] legitimate concerns about fraud, present evidence and take it to court.” And then longtime Trump ally Chris Christie, former Republican governor of New Jersey, complained bluntly, “Show us the evidence.” By the eve of the second impeachment trial in February 2021, the question whether the Senate would hear live evidence was prominently discussed and debated, albeit with the expected but perhaps depressing conclusion that the Senate would make its decision without listening to any such evidence at all.
Although some politicians and news outlets are to be commended for noticing the importance of evidence, public and political discussions of evidence tend to employ a loose and superficial view of what evidence is, where it comes from, and how it should be evaluated. All too frequently, for example, commentators on a variety of issues conflate the lack of evidence with falsity—taking the absence of evidence as being equivalent to evidence that the statement is false. That looseness needs to be inspected. Similarly, public discourse often couples the idea of evidence with any of numerous qualifying and annoyingly confusing adjectives. Phrases such as “hard evidence,” “direct evidence,” “concrete evidence,” “conclusive proof,” and many others all suggest, misleadingly, that the lack of overwhelming proof beyond a reasonable doubt for some conclusion is sufficient to reject a conclusion for which there actually is at least some evidence. This common phenomenon also needs more rigorous examination, as does the role of experts—not only in using evidence, but also in reaching conclusions that then serve as evidence for the decisions of those who lack the requisite expertise. In response to current events, we often see officials and others display a dangerous lack of respect for the evidentiary conclusions of genuine experts, but these events also sometimes endow professionals, experts, and expert institutions with an authority that extends well beyond the scope of their expertise.
A further inspiration for this book is my own experience decades ago as a trial lawyer dealing with the law of evidence on a daily basis, followed by more than forty years of teaching, studying, and writing about the law of evidence. This book is not about law, but it draws on the law as a source of occasional wisdom and more than occasional illuminating examples.
It would be ironic if a book on evidence were to underestimate the importance of providing evidence for its assertions. Consequently I have made every effort to provide references for the analysis and arguments that follow. Extensive notes not only provide support for what is claimed in the text. They can also be useful for the reader who would like to go further or deeper than the flow of the text permits. And, most importantly, what will appear to some as excessive referencing is my way of recognizing that whatever insight may be found here builds on the previous insights of others. For this purpose, even if for no other, too many references are far preferable to too few.
The good news for most readers is that the notes providing these references and the occasional marginally useful digressions are endnotes and not footnotes. The text is designed to be read without referring to the notes—which spares the reader the distraction of going back and forth between text and notes, like watching a tennis match from midcourt—but a quick scan of the notes after reading each chapter may allow the interested reader to see if anything in the notes provides useful elaboration.
This book, like my previous books, has been written as a book, and not as a loosely stitched together and only lightly revised collection of previously published articles. Writing a book from scratch requires time and resources. I am grateful to the University of Virginia School of Law, and more specifically the University of Virginia School of Law Foundation and the generous alumni and friends who fund its efforts, for providing the support that has made this possible. And although this book does not collect previous publications, some of the ideas and topics examined here have emerged in my earlier writings and presentations. Accordingly, I am happy to express my gratitude for audience comments at Dartmouth College, Harvard University, the University of Chicago, Rutgers University, the University of Surrey, the University of California at Los Angeles, the University of Texas, the University of Virginia, Universidad Autónoma de México, the Max Planck Institute for Research on Collective Goods (Bonn), the Duck Conference on Social Cognition, the MacArthur Foundation Project on Law and Neuroscience, the Jurisprudence Discussion Group at the University of Oxford, the World Congress on Evidential Reasoning at Girona University, and the 28th (Lisbon) and 29th (Lucerne) World Congresses of the International Association for Philosophy of Law and Social Philosophy. Comments on these papers and presentations by Ron Allen, Amalia Amaya, David Bernstein, Ruth Chang, Damiano Canale, David Enoch, Valentin Hartmann, Sarah Moss, Michael Pardo, Martin Rechenauer, and Levi Spectre have been particularly helpful. So too have less formal but just as valuable conversations with numerous colleagues at the University of Virginia School of Law, especially my colleague, friend, and office neighbor John Harrison. His repository of knowledge about what seems like everything is matched only by his genuine curiosity about the few things he does not know. Impressively detailed constructive comments from two anonymous reviewers for Harvard University Press have also been of great assistance in producing the final draft. And Barbara Spellman, herself a prominent teacher and scholar of the psychology and law of evidence, has saved me from numerous substantive errors as well as from my unfortunate tendency to think that no sentence has ever been hurt by making it longer.