In their book The Enigma of Reason, out last April, Hugo Mercier and Dan Sperber have written an important book on an important but neglected topic. They argue first that humans, and only humans, have a brain module that handles abstract reasoning:

Reason is indeed [a] specialized [module of inference]; it draws interpretive inferences just about reasons.

Second, they argue for a new theory of reason. Previously, scholars have focused on reason in the context of a sincere attempt to infer truth:

Most of the philosophers and psychologists we talked to endorse some version of the dominant intellectualist view: they see reason as a means to improve individual cognition and arrive one one’s own at better beliefs and decisions. Reason, they take for granted, should be objective and demanding.

In this view, observed defects in human reasoning are to be seen as understandable errors, accommodations to complexity, and minor corrections due to other minor selection pressures. Sincerely inferring truth is the main thing. Mercier and Sperber, however, argue that one social correction isn’t at all minor: reason is better understood in the context of a speaker who is trying to a persuade a listener who sincerely seeks to infer truth. Speaker “biases” are just what one should expect from speakers seeking to persuade:

In our interactionist account, reason’s bias and laziness aren’t flaws; they are features that help reason fulfill its function. People are biased to find reasons that support their point of view because this is how they can justify their action and convince others to share their beliefs.

Mercier and Sperber do successfully show that many “defects” in human reasoning can be understand as arising from insincere speaker motives. However, just as we can question speakers motives, we can also question listener motives. Couldn’t listeners also be also concerned about the social consequences of their inferences? Listeners might want to agree to show submission or favor to a speaker, and ignore or disagree to show disfavor or dominance. And listeners may want to agree with what they expect others to agree with, to sound reasonable and to show loyalty.

Mercier and Sperber seem to be aware of many such listener motives:

Luria used problems that were logically trivial but .. unfamiliar:

In the Far North, where there is snow, all bears are white. Novaya Zemlya is in the Far North. What color are bears there?

When unschooled peasants were interviewed, the vast majority seemed at a loss, providing answers such as “There are many sorts of bears.” .. His experiments were successfully replicated with several unschooled populations. .. In small-scale populations, people are very cautious with their assertions, only stating a position when they have a good reason to. .. Only a fool with dare to make such a statement .. she could not appropriately defend. ..

Because of the intense pressure to maintain social harmony, “the Japanese are not trained to argue and reason.” ..

The overlap between the proper and the actual domain of reasoning remains partial. There are false negatives: people in a dominant position or in the vocal majority might pay little attention to the opinion of subordinates or minorities and fail to detect disagreements. There are also false positives; either clashes of ideas that occur between third parties with whom we are not in a position to interact … or clashes of ideas within oneself. ..

Throughout the centuries, smart physicians felt justified in making decisions that cost patients their lives. .. If they were eager to maintain their reputation, they were better off bleeding their patients. ..

You might be ill-judged by people who are not aware of this argument, and you might not have the opportunity to explain the reason for your choice.

Mercier and Sperber treat these various effects as minor corrections that don’t call into question their basic theory, even as they complain that the traditional view of reason doesn’t attend enough to certain effects that their theory explains. But it seems to me that in addition to explaining some effects as due to insincere speaker motives, a better theory of reason could also explain other effects as due to insincere listener motives.

In the modern world, while we usually give lip service to the idea that we are open to letting anyone persuade us on anything with a good argument, by the time folks get to be my age they know that such openings are in fact highly constrained. For example, early on in my relation with my wife she declared that as I was better at arguing, key decisions were just not going to be made on the basis of better arguments.

Even in academia, little value is placed on simple relevant arguments, compared to demonstrating the mastery of difficult tools. And in our larger world, the right to offer what looks like a critical argument is usually limited to the right sort of people who have the right sort of relation in the right sort of contexts. Even then people know to avoid certain kinds of arguments, even if those arguments would in fact persuade if pushed hard enough. And most speakers know they are better off arguing for what listeners want to believe, rather than for unpleasant conclusions.

Mercier and Sperber suggest that arguing used to be different, and better:

When a collective decision has to be made in a modern democracy, people go to the voting booth. Our ancestors sat down and argued – at least if present-day small-scale societies are any guide to the past. In most such societies across the globe, when a grave problem threatens the group, people gather, debate, and work out a solution that most find satisfying. ..

When the overriding concern of people who disagree is to get things right, argumentation should not only make them change their mind, it should make them change their mind for the best.

I’d like to believe that argumentation was all different and better back then, with careful speakers well disciplined by sincere listeners. But I’m skeptical. I expect that the real selection pressures on our abilities to reason have always reflected these complex social considerations, for both speakers and listeners. And we won’t really understand human reasoning until we think through what reasoning behaviors respond well to these incentives.