Rationality ought to be the lodestar for everything we think and do. (If you disagree, are your objections rational?) Yet in an era blessed with unprecedented resources for reasoning, the public sphere is infested with fake news, quack cures, conspiracy theories, and “post-truth” rhetoric.
How can we make sense of making sense—and its opposite? The question is urgent. In the third decade of the third millennium, we face deadly threats to our health, our democracy, and the livability of our planet. Though the problems are daunting, solutions exist, and our species has the intellectual wherewithal to find them. Yet among our fiercest problems today is convincing people to accept the solutions when we do find them.
Commentaries by the thousands have lamented our shortfall of reason, and it’s become conventional wisdom that people are simply irrational. In social science and the media, the human being is portrayed as a caveman out of time, poised to react to a lion in the grass with a suite of biases, blind spots, fallacies, and illusions. (The Wikipedia entry for cognitive biases lists almost two hundred.)
Yet as a cognitive scientist I cannot accept the cynical view that the human brain is a basket of delusions. Hunter-gatherers—our ancestors and contemporaries—are not nervous rabbits but cerebral problem solvers. A list of the ways in which we’re stupid can’t explain why we’re so smart: smart enough to have discovered the laws of nature, transformed the planet, lengthened and enriched our lives, and, not least, articulated the rules of rationality that we so often flout.
To be sure, I am among the first to insist that we can understand human nature only by considering the mismatch between the environment in which we evolved and the environment we find ourselves in today. But the world to which our minds are adapted is not just the Pleistocene savannah. It’s any nonacademic, nontechnocratic milieu—which is to say, most of human experience—in which the modern instruments of rationality like statistical formulas and datasets are unavailable or inapplicable. As we shall see, when people are given problems that are closer to their lived reality and framed in the ways in which they naturally encounter the world, they are not as witless as they appear. Not that this gets us off the hook. Today we do have refined instruments of reason, and we are best off, as individuals and as a society, when we understand and apply them.
This book grew out of a course I taught at Harvard which explored the nature of rationality and the puzzle of why it seems to be so scarce. Like many psychologists, I love to teach the arresting, Nobel Prize–winning discoveries of the infirmities that afflict human reason, and consider them to be among the deepest gifts to knowledge that our science has contributed. And like many, I believe that the benchmarks of rationality that people so often fail to measure up to should be a goal of education and popular science. Just as citizens should grasp the basics of history, science, and the written word, they should command the intellectual tools of sound reasoning. These include logic, critical thinking, probability, correlation and causation, the optimal ways to adjust our beliefs and commit to decisions with uncertain evidence, and the yardsticks for making rational choices alone and with others. These tools of reasoning are indispensable in avoiding folly in our personal lives and public policies. They help us calibrate risky choices, evaluate dubious claims, understand baffling paradoxes, and gain insight into life’s vicissitudes and tragedies. But I knew of no book that tried to explain them all.
The other inspiration for this book was my realization that for all its fascination, the cognitive psychology curriculum left me ill equipped to answer the questions I was most frequently asked when I told people I was teaching a course on rationality. Why do people believe that Hillary Clinton ran a child sex ring out of a pizzeria, or that jet contrails are really mind-altering drugs dispersed by a secret government program? My standard lecture bullet points like “the gambler’s fallacy” and “base-rate neglect” offered little insight into just the enigmas that are making human irrationality so pressing an issue today. Those enigmas drew me into new territories, including the nature of rumor, folk wisdom, and conspiratorial thinking; the contrast between rationality within an individual and in a community; and the distinction between two modes of believing: the reality mindset and the mythology mindset.
Finally, though it may seem paradoxical to lay out rational arguments for rationality itself, it’s a timely assignment. Some people pursue the opposite paradox, citing reasons (presumably rational ones, or why should we listen?) that rationality is overrated, such as that logical personalities are joyless and repressed, analytical thinking must be subordinated to social justice, and a good heart and reliable gut are surer routes to well-being than tough-minded logic and argument. Many act as if rationality is obsolete—as if the point of argumentation is to discredit one’s adversaries rather than collectively reason our way to the most defensible beliefs. In an era in which rationality seems both more threatened and more essential than ever, Rationality is, above all, an affirmation of rationality.
A major theme of this book is that none of us, thinking alone, is rational enough to consistently come to sound conclusions: rationality emerges from a community of reasoners who spot each other’s fallacies. In that spirit I thank the reasoners who made this book more rational. Ken Binmore, Rebecca Newberger Goldstein, Gary King, Jason Nemirow, Roslyn Pinker, Keith Stanovich, and Martina Wiese incisively commented on the first draft. Charleen Adams, Robert Aumann, Joshua Hartshorne, Louis Liebenberg, Colin McGinn, Barbara Mellers, Hugo Mercier, Judea Pearl, David Ropeik, Michael Shermer, Susanna Siegel, Barbara Spellman, Lawrence Summers, Philip Tetlock, and Juliani Vidal reviewed chapters in their areas of expertise. Many questions arose as I planned and wrote the book, and they were answered by Daniel Dennett, Emily-Rose Eastop, Baruch Fischhoff, Reid Hastie, Nathan Kuncel, Ellen Langer, Jennifer Lerner, Beau Lotto, Daniel Loxton, Gary Marcus, Philip Maymin, Don Moore, David Myers, Robert Proctor, Fred Shapiro, Mattie Toma, Jeffrey Watumull, Jeremy Wolfe, and Steven Zipperstein. I counted on the expert transcription, fact-checking, and reference hunting by Mila Bertolo, Martina Wiese, and Kai Sandbrink, and on original data analyses by Bertolo, Toma, and Julian De Freitas. Also appreciated were the questions and suggestions from the students and teaching staff of General Education 1066: Rationality, especially Mattie Toma and Jason Nemirow.
Special thanks go to my wise and supportive editor, Wendy Wolf, for working with me on this book, our sixth; to Katya Rice, for copy-editing our ninth; and to my literary agent, John Brockman, for his encouragement and advice on our ninth. I appreciate as well the support over many years from Thomas Penn, Pen Vogler, and Stefan McGrath of Penguin UK. Ilavenil Subbiah once again designed the graphics, and I thank her for her work and her encouragement.
Rebecca Newberger Goldstein played a special role in the conception of this book, because it is she who impressed on me that realism and reason are ideals that must be singled out and defended. Love and gratitude go as well to the other members of my family: Yael and Solly; Danielle; Rob, Jack, and David; Susan, Martin, Eva, Carl, and Eric; and my mother, Roslyn, to whom this book is dedicated.