The Enigma of Reason: A New Theory of Human Understanding

by Dan Sperber

  When we listen to others, then, we should trust wisely and sometimes distrust. When we talk to others, we often have to overcome their understandable lack of trust. If we distrusted others only when they don’t deserve our trust, things would be for the best. Often, however, we withhold our trust out of prudence, not because we know that others are untrustworthy but because we are not sure that we can trust them. This reticence may be wise—better safe than sorry—but still, we miss valuable information. Communication, which could be beneficial to speakers and listeners alike, often falters for lack of confidence.

  The second function of reason—a function carried out through reasoning and argumentation—is, we claim, to make communication effective even when the communicators lack sufficient credibility in the eyes of their audience to be believed on trust. Reason produces reasons that communicators use as arguments to persuade a reticent audience. Reason, by the same token, helps a cautious audience evaluate these reasons, accept good arguments, and reject bad ones.

  Much of our earlier joint work focused on this argumentative function of reason and developed an “argumentative theory of reasoning.”3 In this book, we broaden our perspective, consider both the argumentative and the justificatory functions of reason, and develop an interactionist approach to the mechanisms and the two functions of reason.

  Part IV, “What Reason Can and Cannot Do,” offers a tour of what reason does. Throughout this tour, we show how our interactionist perspective is in a good position to explain why reason behaves the way it does. We revisit some well-established but ill-explained apparent weaknesses of reason such as the confirmation bias. We also draw attention to some of its neglected strengths.

  The tour starts with a pair of observations: human reason is both biased and lazy. Biased because it overwhelmingly finds justifications and arguments that support the reasoner’s point of view, lazy because reason makes little effort to assess the quality of the justifications and arguments it produces. Imagine, for instance, a reasoner who happens to be partial to holidays at the beach. When reasoning about where to spend her next vacation, she will spontaneously accumulate reasons to choose a sunny place by the sea, including reasons that are manifestly poor (say, that there’s a discount on the flight to the very place where she would like to go, when in fact the same discount applies to many other destinations as well).

  The solitary use of reason has two typical outcomes. When the reasoner starts with a strong opinion, the reasons that come to her mind tend all to support this opinion. She is unlikely, then, to change her mind; she might even become overconfident and develop stronger opinions. But sometimes a reasoner starts with no strong opinion, or with conflicting views. In this case, reason will drive her toward whatever choice happens to be easier to justify, and this sometimes won’t be the best choice. Imagine she has a choice between visiting her horrible in-laws and then vacationing at the beach, or starting with the beach and then going to see the in-laws, the latter option being somewhat cheaper. Reason will drive her toward what seems to be the rational decision: taking the cheaper option. It is likely, however, that she would come back more satisfied if she started with the in-laws instead of letting the prospect of this visit spoil her time at the beach: a better choice overall, but involving a hard-to-justify extra expense.

  Psychologists generally recognize that reason is biased and lazy, that it often fails to correct mistaken intuitions, and that it sometimes makes things worse. Yet most of them also maintain that the main function of reason is to enhance individual cognition—a task it performs abysmally. The interactionist perspective, on the other hand, offers for the first time an evolutionarily plausible account of the often decried biases and shortcomings of reason.

  It makes sense, we will show, for a cognitive mechanism aimed at justifying oneself and convincing others to be biased and lazy. The failures of the solitary reasoner follow from the use of reason in an “abnormal” context. Underwater, you wouldn’t expect a pen—which wasn’t designed to work there—or human lungs—which didn’t evolve to work there either—to function properly. Similarly, take reason out of the interactive context in which it evolved, and nothing guarantees that it will yield adaptive results.

  What, then, happens when reason is put back in its “normal” environment, when it gets to work in the midst of a discussion, as people exchange arguments and justifications with each other? In such a context it properly fulfills the functions for which it evolved. In particular, when people who disagree but have a common interest in finding the truth or the solution to a problem exchange arguments with each other, the best idea tends to win; whoever had it from the start or came to it in the course of the discussion is likely to convince the others. This conclusion might sound unduly optimistic, but it is supported by a wide range of evidence, from students discussing logical problems, to juries deliberating, and to forecasters trying to predict where the next war will erupt.

  In the last three chapters (Part V, “Reason in the Wild”) we demonstrate how robust are the features and effects of reason reviewed earlier. We find that solitary reasoning is biased and lazy, whereas argumentation is efficient not only in our overly argumentative Western societies but in all types of cultures, not only in educated adults but also in young children. Few will be surprised to hear that reason is typically biased and lazy when it is applied to moral and political issues. More surprising may be evidence that shows how, even in the moral and political realms, argumentation may work quite efficiently, allowing participants to form more accurate moral judgments and citizens to form more enlightened opinions. Such findings, however, are what one should expect in an interactionist perspective.

  The last chapter (Chapter 18, “Solitary Geniuses?”) is about science, generally considered the pinnacle of human reason. Science is exceptional in many ways, but is the way scientists reason itself exceptional? Scientific progress is often attributed to solitary geniuses, from Newton to Darwin or Einstein. Their superior reason, we are told, doesn’t suffer from the shortcomings that plague the rest of us. Not only can these geniuses dispense with discussions with others in order to come up with new theories, such discussion might even hinder them when their revolutionary insights would be misunderstood and scorned by their not-quite-peers. Better wait for a less prejudiced new generation to see the light. Fortunately (for our theory and for scientists), science doesn’t work this way. Scientists make do with the same reason that all humans use, with its biases and limitations. But they also benefit from its strengths and in particular from the fact that reason is more efficient in evaluating good arguments than in producing them: when the arguments are there, the scientific community is able to elevate the status of a new theory from fringe to textbook material in a few years.

  In these five parts and eighteen chapters, what we will put to you, then, is an interactionist approach to reason that contrasts with standard intellectualist approaches: reason, we maintain, is first and foremost a social competence. We do not deny that reason can bring huge intellectual benefits, as the case of science well illustrates; on the contrary, we explain how it does this: through interaction with others.

  You are unlikely to accept what we say just because we say it, so we will present you with arguments that you will be able to assess on their own merits. We will show you how considering reason as a mechanism that draws intuitive inferences about reasons solves the first half of the enigma: reason is not a superpower implausibly grafted onto an animal mind; it is, rather, a well-integrated component of the extraordinarily developed mind that characterizes the human animal.

  To resolve the second half of the enigma, we will demonstrate how apparent biases that have been described as deplorable flaws of reason are actually features well adapted to its argumentative function. A number of sometimes surprising predictions about human reason follow from our approach. The evidence we will present confirms these predictions. It is by force of argument that we hope to persuade you that the interactionist approach
is right or, at least, on the right track. This, of course, makes the book itself an illustration of the perspective it defends.

  I

  * * *

  SHAKING DOGMA

  Reason, the faculty that gives humans superior knowledge and wisdom? This dominant view in the Western tradition has been radically undermined by fifty years of experimental research on reasoning. In Chapters 1 and 2, we show how old dogmas were shaken, but not nearly enough. The now dominant view of reasoning (“dual process” or “fast and slow thinking”), however appealing, is but a makeshift construction amid the ruins of old ideas.

  1

  Reason on Trial

  In the cold autumn of 1619, René Descartes, then aged twenty-three and a volunteer in the armies of the Duke of Bavaria, found himself in what is now southern Germany with time to spend and nobody around he deemed worth talking to. There, in a stove-heated room, as he recounts in his Discourse on Method,1 he formed the stunningly ambitious project of ridding himself of all opinions, all ideas learned from others, and of rebuilding his knowledge from scratch, step by step. Reason would be his sole guide. He would accept as true only what he could not doubt.

  Descartes justified his rejection of everything he had learned from others by expressing a general disdain for collective achievements. The best work, he maintained, is made by a single master. What one may learn from books, he considered, “is not as close to the truth, composed as it is of the opinions of many different people, as the simple reasoning that any man of good sense can produce about things in his purview.”2

  Descartes would have scorned today’s fashionable idea of the “wisdom of crowds.” The only wisdom he recognized, at least in the sciences, was that of individual reason: “As long as one stops oneself taking anything to be true that is not true and sticks to the right order so as to deduce one thing from another, there can be nothing so remote that one cannot eventually reach it, nor so hidden that one cannot discover it.”3

  Why did Descartes decide to trust only his own mind? Did he believe himself to be endowed with unique reasoning capacities? On the contrary, he maintained that “the power of judging correctly and of distinguishing the true from the false (which is properly what is called good sense or reason) is naturally equal in all men.”4 But if we humans are all endowed with this power of distinguishing truth from falsity, how is it that we disagree so much on what is true?

  “The Greatest Minds Are Capable of the Greatest Vices as Well as the Greatest Virtues”

  Most of us think of ourselves as rational. Moreover, we expect others to be rational too. We are annoyed, sometimes even angry, when we see others defending opinions we think are deeply flawed. Hardly ever do we assume that those who disagree with us altogether lack reason. What aggravates us is the sense that these people do not make a proper use of the reason we assume they have. How can they fail to understand what seems so obvious (to us)?

  If reason is this highly desirable power to discover the truth, why don’t people endowed with it use it to the best of their capacities all the time? After all, we expect all sighted people to see what others see. Show several people a tree or a sunset, and you expect them all to see a tree or a sunset. Ask, on the other hand, several people to reason about a variety of questions, from logical problems to social issues, and what might surprise you is their coming to the same conclusions. If reason, like perception, worked to provide us with an adequate grasp of the way things really are, this should be deeply puzzling.

  Descartes had an explanation: “The diversity of our opinions arises not from the fact that some of us are more reasonable than others, but solely that we have different ways of directing our thoughts, and do not take into account the same things …. The greatest minds are capable of the greatest vices as well as the greatest virtues.”5

  This, however, is hardly more than a restatement of the enigma, for shouldn’t the way we direct our thoughts itself be guided by reason? Shouldn’t reason, in the first place, protect us from intellectual vices?

  Descartes was the most forceful of reason’s many advocates. Reason has also had many, often passionate, detractors. Its efficacy has been questioned. Its arrogance has been denounced. The religious reformer Martin Luther was particularly scathing: “Reason is by nature a harmful whore. But she shall not harm me, if only I resist her. Ah, but she is so comely and glittering …. See to it that you hold reason in check and do not follow her beautiful cogitations. Throw dirt in her face and make her ugly.”6

  To be fair, Descartes’s and Luther’s views on reason were much richer and subtler than these isolated quotes suggest, and hence less diametrically opposed. Luther’s invectives were aimed at the claims of reason in matters of faith. In a different context, the same Luther described reason, much more conventionally, as “the inventor and mentor of all the arts, medicines, laws, and of whatever wisdom, power, virtue, and glory men possess in this life” and as “the essential difference by which man is distinguished from the animals and other things.”7 Descartes for his part abstained, out of conviction or out of prudence, from critically examining faith in the light of reason.

  Still, if reason were put on trial, both the prosecution and the defense could make an extraordinary case. The defense would argue, citing Descartes, Aristotle, Kant, or Popper, that humans err by not reasoning enough. The prosecution would argue, citing Luther, Hume, Kierkegaard, or Foucault, that they err by reasoning too much.

  The defense and the prosecution could also produce compelling narratives to bolster their case.

  Eratosthenes and the Unabomber

  Do you doubt the power of reason? Just look at the sciences, the defense would exclaim. Through insightful reasoning, scientists have discovered hidden facts and deep explanations that would have been completely inaccessible otherwise. Modern science provides countless examples of the power of reason, but nothing beats, as a simple and compelling illustration, the measurement of the circumference of the earth twenty-two centuries ago, by Eratosthenes (276–195 BCE), the head librarian of the greatest library of the ancient world at Alexandria in Egypt.8

  Already at the time, it was commonly accepted that the earth was spherical rather than flat. This best explained the curvature of the horizon at sea and the apparent movement of the sun and the stars. Still, it was, as the phrase goes, “just a theory.” No one had traveled around the earth, let alone seen it from a distance as astronauts now have. How, then, could its circumference be measured?

  Eratosthenes had heard that every year, on a single day, at noon, the sun shone directly to the bottom of wells in the distant town of Syene (now Aswan). This, he understood, meant that, there and then, the sun was at the zenith, vertically above the town. Syene therefore had to be on the Tropic of Cancer and that single day had to be the summer solstice (our June 21). Syene, he assumed, was due south on the same meridian as Alexandria. He knew how long it took caravans to travel from Alexandria to Syene and, on that basis, estimated the distance between the two cities to be 5,014 stades (an ancient unit of measure).

  When, on the summer solstice at noon, the sun was vertically above Syene, by how many degrees was it south of the vertical in the more northern city of Alexandria? Eratosthenes measured the length of the shadow cast at that very moment by an obelisk located in front of his library (or so the story goes). He determined that the sun’s rays were hitting the obelisk at an angle of 7.2 degrees south of the vertical. He understood that the sun was far enough to treat all rays that reach the earth as parallel, and that therefore the angle between the rays of the sun and the vertical at Alexandria was equal to the angle between the vertical at Alexandria and that at Syene, two lines that cross at the center of the earth (see Figure 2). In other words, that very angle of 7.2 degrees also measured the difference in degrees of latitude between Alexandria and Syene. He now had all the information he needed. Since 7.2 degrees is one-fiftieth of 360 degrees, Eratosthenes could calculate the circumference of the earth by multiplying by fifty th
e distance between Alexandria and Syene. The result, 252,000 stades, is 1 percent shy of the modern measurement of 24,859 miles, or 40,008 kilometers.9

  Eratosthenes grasped the mutual relevance of apparently unrelated pieces of evidence (the pace of caravans, the sun shining to the bottom of wells, the shadow of an obelisk), of assumptions (the rotundity of the earth, its distance from the sun), and of simple geometrical ideas about angles and parallel lines. He drew on all of them to measure a circumference that he could imagine but neither see nor survey. What made his measurement not just true but convincing is—isn’t it?—that it was a pure product of human reason.

  How telling, the prosecution would object, that the defense of reason should choose as evidence such an exceptional achievement! It is an exception, and this is why it is still remembered after more than two thousand years. Ordinary reasoning doesn’t lead us far, and that is just as well, as often it leads in the wrong direction. Even extraordinary uses of reason, far from being all on the model of Eratosthenes, have led many thinkers badly astray. Publishers, newspapers, and scientific journals receive every day the thoroughly reasoned nonsense of would-be philosophers, scientists, or reformers who, failing to get their work published there, then try the World Wide Web. Some of them, however, reason not just to theoretical but also to practical absurdities, act on them, and achieve notoriety or even infamy. The prosecution might well at this juncture introduce the case of Ted Kaczynski.