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The Enigma of Reason by Hugo Mercier and Dan Sperber

We descend from the divine to the human as Peter Stone reasons about the purpose and uniqueness of human reason.

According to the journalist H.L. Mencken, every complex problem has a solution that is clear, simple, and wrong. The Enigma of Reason: A New Theory of Human Understanding by cognitive scientists Hugo Mercier and Dan Sperber is devoted to examining one such problem and solution. The problem in question is, Why did human beings develop the capacity to reason? The solution, defended by philosophers throughout the ages and by most psychologists today, is that “reason seems to have an obvious function: to help individuals achieve greater knowledge and make better decisions on their own” (p.175). The goal of The Enigma of Reason is to show why this solution doesn’t work, and why an alternative explanation makes better sense.

So what’s wrong with the traditional idea that “the job of reasoning is to help individuals achieve greater knowledge and make better decisions” (p.4)? Two things, actually. The first is that the traditional explanation makes reason out to be a veritable Darwinian superpower, an obvious boon for any animal, living in any environment. It’s not like echolocation, say, which is only useful for animals like bats which live in environments with very little light, but more like sight, which is useful in a wide range of environments, and which has evolved independently many times. Why, then, haven’t other animals developed the ability to reason to an equivalent level? Why should such a useful faculty have only developed once? “Understanding why only a few species have echolocation is easy,” write Mercier and Sperber, “Understanding why only humans have reason is much more challenging” (p.2). The second difficulty is that if human beings developed the capacity to reason in order to help them make better decisions, then why don’t we make better decisions? Psychological study after psychological study has demonstrated what most of us know from experience: that “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” (p.9). Mercier and Sperber conclude that “Reason as standardly understood is doubly enigmatic. It is not an ordinary mental mechanism but a cognitive superpower that evolution… has bestowed only on us humans. As if this were not enigmatic enough, the superpower turns out to be flawed. It keeps leading people astray. Reason, a flawed superpower. Really?” (p.4).

So the goal of The Enigma of Reason is to develop a “new scientific understanding of reason, one that solves the double enigma.” Mercier and Sperber then endeavour to show that reason, “far from being a strange cognitive add-on, a superpower gifted to humans by some improbable evolutionary quirk, fits quite naturally among other human cognitive capacities and, despite apparent evidence to the contrary, is well adapted to its true function” (p.5). So they hope to explain both why humans – and only humans – evolved the ability to reason, and exactly what reason does for us.

What is Reason, Really?

In order to do this, however, they first must define just what reason is. According to Mercier and Sperber, reason should be regarded as “one module of inference among many” (p.328).

All animals make use of inference, defined as “the extraction of new information from information already available” (p.53). Whenever an herbivore, for example, sees or smells a type of plant, and concludes that the plant is food, or poison, it engages in inference. An animal that couldn’t infer anything would have a very short lifespan indeed.

This doesn’t mean, of course, that a cow sees grass and thinks to itself, ‘I can eat that’. Most of the inferring done by animals is nonconscious. Indeed, conscious inference is the exception rather than the rule. But between fully conscious and fully nonconscious inference lies a significant grey area, within which falls intuition. On the one hand, “The content of an intuition is conscious.” But on the other hand, “One has little or no knowledge of reasons for one’s intuitions, but it is taken for granted that there exist such reasons and that they are good enough to justify the intuition, at least to some degree” (p.66). Put another way, an intuition tells you to believe something – indeed, it often tells you it very confidently (even though it could be mistaken) – but it doesn’t tell you why you should believe it. Mercier and Sperber describe intuitions as “mental icebergs: we may only see the tip but we know that, below the surface, there is much more to them, which we don’t see” (p.7).

Reason is often contrasted with intuition, as though they were fundamentally different – even opposed – in nature. This is a mistake, argue Mercier and Sperber, as reason is in fact a specialized form of intuition: “Reason,” they write, “is a mechanism for intuitive inference about one kind of representations, namely, reasons” (p.7). Reason gives you an intuition that X counts as a reason for believing Y. It doesn’t, however, give you a reason why X counts as a reason for believing Y. Further reflection, of course, may turn up such a reason; but if it does, then that further reason will itself be an intuition.

It couldn’t be any other way, argue Mercier and Sperber. If we couldn’t rely on our intuitions about reasons, we’d have to have a reason W for believing that X counts as a reason for Y, and then a reason V for believing that W counts as a reason for believing that X counts as a reason for Y, and so on and so on forever. As Mercier and Sperber note, this is the paradox that Lewis Carroll explored in a fun paper entitled ‘What the Tortoise Said to Achilles’ (p. 131-132).

For Mercier and Sperber, then, “reasoning is not an alternative to intuitive inference; reasoning is a use of intuitive inferences about reasons” (p.133). The question then becomes, why did humans, and no other species, develop this capacity?

question mark
Question mark word art © John Hain 2014 public domain

The Society of Human Reason

As noted, the answer can’t be because it helps individuals to draw inferences better on their own: if so, we’d all be better at it by now. Instead, “Reasons are primarily for social consumption” (p.127). That is, reasons, according to Mercier and Sperber, serve two major social functions – a justificatory function, and an argumentative function.

The justificatory function arose because we all care what other people think of us. If they are to trust us and cooperate with us, other people need to know why we do what we do. Reasoning makes it possible for us to explain ourselves to others, and to evaluate the explanations others give us about their own behaviour. As they say, “Giving reasons to justify oneself and reacting to the reasons given by others are, first and foremost, a way to establish reputations and coordinate expectations” (p.143).

The argumentative function matters because we care what other people both believe and do. We often like them to do things we want, or to share certain beliefs that we also have, but they might not be naturally inclined to do so. It therefore helps us to be able to give people reasons why they ought to agree with us in either case. And reason also helps people evaluate the reasons given them; otherwise, we’d be putty in the hands of any con artist. Reasoning thus has “a double argumentative function: for a communicator, reasoning is a means to produce arguments in order to convince a vigilant audience; for the audience, reasoning is a means to evaluate these arguments and accept them when good, or reject them when bad” (p.288).

For Mercier and Sperber, therefore, reason is “first and foremost a social competence” (p.11): “We produce reasons in order to justify our thoughts and actions to others and to produce arguments to convince others to think and act as we suggest. We also use reason to evaluate not so much our own thought as the reasons others produce to justify themselves or to convince us” (p.7). This theory, they contend, explains perfectly the doubly enigmatic nature of reason. Why did humans, and no other species, evolve the capacity to reason? Because we are an incredibly social – indeed, a hypersocial – species. No other species engages in the level of complex social coordination that the human race has been practicing since its earliest days. “Reason is an adaptation to the hypersocial niche humans have built for themselves,” they explain (p.33).

The theory also tells us why solitary human beings prove so bad at reasoning: for the same reason that people prove so bad at breathing underwater. “In our interactionist approach, the normal conditions for the use of reasoning are social, and more specifically dialogic. Outside of this environment, there is no guarantee that reasoning acts for the benefits of the reasoner…This does not mean reasoning is broken, simply that it has been taken out of its normal conditions” (p.247). Under the right conditions, however, people are very good at calling each other out for making poor arguments and engaging in sloppy reasoning. Indeed, the scientific community has developed this social practice to a high art-form: it’s what makes possible the incredible knowledge which that community has attained. Without other people to call them out when they go wrong, even the brightest of scientific minds can go painfully astray. Just ask Linus Pauling, the only person to win two Nobel Prizes, about his bizarre conviction that vitamin C could prevent cancer – a conviction he didn’t abandon even after his own cancer diagnosis (pp.205-207).

There is much more that could be said about The Enigma of Reason, an incredibly rich and complex book that musters an extraordinary array of scientific and philosophical evidence, but I will end this examination of the book on a philosophical note. Mercier and Sperber say that one of the first great philosophers of the Western tradition, Socrates, understood the social nature of argument very well indeed, and that for early philosophers in this tradition, such as Plato, “Socratic reasoning could be seen as reasoning par excellence” (p.197). Philosophy took a different turn, however, with Aristotle, who provided a new image of the typical reasoner: “Rather than Socrates trying to convince his interlocutor and the interlocutor understanding the force of Socrates’ argument, the paradigm of a reasoner became the scientist reasoning on his own (more rarely on her own) to arrive at a better understanding of the world” (p.198). So if Mercier and Sperber are to be believed, if we want to understand reason properly, we need to be a little more Socratic and a little less Aristotelian.

© Peter Stone 2022

Peter Stone is an associate professor in political science at Trinity College Dublin. The second edition of his book Bertrand Russell: Public Intellectual (co-edited with Tim Madigan) was recently published by Tiger Bark Press.

The Enigma of Reason: A New Theory of Human Understanding, Dan Sperber, Hugo Mercier, Allen Lane, 2017, £6.99 pb, 416 pages, ISBN: 9781846145575

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