"Why do humans reason" (PDF), a paper by Hugo Mercier and Dan Sperber, reviewing an impressive amount of research with a lot of overlap with themes previously explored on Less Wrong, suggests that our collective efforts in "refining the art of human rationality" may ultimately be more successful than most individual efforts to become stronger. The paper sort of turns the "fifth virtue" on its head; rather than argue in order to reason (as perhaps we should), in practice, we reason in order to argue, and that should change our views quite a bit.

I summarize Mercier and Sperber's "argumentative theory of reasoning" below and point out what I believe its implications are to the mission of a site such as Less Wrong.

Human reasoning is one mechanism of inference among others (for instance, the unconscious inference involved in perception). It is distinct in being a) conscious, b) cross-domain, c) used prominently in human communication. Mercier and Sperber make much of this last aspect, taking it as a huge hint to seek an adaptive explanation in the fashion of evolutionary psychology, which may provide better answers than previous attempts at explanations of the evolution of reasoning.

The paper defends reasoning as serving argumentation, in line with evolutionary theories of communication and signaling. In rich human communication there is little opportunity for "costly signaling", that is, signals that are taken as honest because too expensive to fake. In other words, it's easy to lie.

To defend ourselves against liars, we practice "epistemic vigilance"; we check the communications we receive for attributes such as a trustworthy or authoritative source; we also evaluate the coherence of the content. If the message contains symbols that matches our existing beliefs, and packages its conclusions as an inference from these beliefs, we are more likely to accept it, and thus our interlocutors have an interest in constructing good arguments. Epistemic vigilance and argumentative reasoning are thus involved in an arms race, which we should expect to result in good argumentative skills.

What of all the research suggesting that humans are in fact very poor at logical reasoning? Well, if in fact "we reason in order to argue", when the subjects are studied in non-argumentative situations this is precisely what we should expect.

Mercier and Sperber argue that, when you look at research that studies people in the appropriate settings, we turn out to be in fact quite good at reasoning when we are in the process of arguing; specifically, we demonstrate skill at producing arguments and at evaluating others' arguments. M&S also plead for the "rehabilitation" of confirmation bias as playing an adaptive, useful role in the production of arguments in favor of an intuitively preferred view.

If reasoning is a skill evolved for social use, group settings should be particularly conducive to skilled arguing. Research findings in fact show that "truth wins": once a group participant has a correct solution they will convince others. A group in a debate setting can do better than its best member.

The argumentative theory, Mercier and Sperber argue, accounts nicely for motivated reasoning, on the model that "reasoning anticipates argument". Such anticipation colors our evaluative attitudes, leading for instance to "polarization" whereby a counter-argument makes us even more strongly believe the original position, or "bolstering" whereby we defend a position more strongly after we have committed to it.

These attitudes are favorable to argumentative goals but actually detrimental to epistemic goals. This is particularly evident in decision-making. Reasoning appears to help people little when deciding; it directs people to the decisions that will be easily justified, not to the best decisions!

Reasoning falls quite short of reliably delivering  rational beliefs and rational decisions, [and] may even be, in a variety of cases, detrimental to rationality.

However, it isn't all bad news. The important asymmetry is between production of arguments, and their evaluation. In groups with an interest in finding correct answers, "truth wins".

If we generalize to problems that do not  have a provable solution, we should expect, if not necessarily truth, at least good arguments to win. [...] People are quite capable of reasoning in an unbiased manner at least when they are evaluating arguments rather than producing them and when they are after the truth rather than after winning a debate.

Becoming individually stronger at sound reasoning is possible, Mercier and Sperber point out, but rare. The best achievements of reasoning, in science or morality, are collective.

If this view of reasoning is correct, a site dedicated to "refining the art of human rationality" should recognize this asymmetry between producing arguments and evaluating arguments and strive to structure the "work" being done here accordingly.

It should encourage individual participants to support their views, and perhaps take a less jaundiced view of "confirmation bias". But it should also encourage the breaking down of arguments into small, separable pieces, so that they can be evaluated and filtered individually; that lines up with the intent behind "debate tools", even if their execution currently leaves much to be desired.

It should stress the importance of "collectively seeking the truth" and downplay attempts at "winning the debate". This, in particular, might lead us to take a more critical view of some common voting patterns, e.g. larger number of upvotes for snarky one-liner replies than for longer and well-thought out replies.

There are probably further conclusions to be drawn from the paper, but I'll stop here and encourage you to read or skim it, then suggest your own in the comments.