In this short comment I ask whether Mercier and Sperber's seminal account of reasoning should change the way we teach and study reasoning--not in cognitive psychology, but in argumentation theory (understood as a cross-disciplinary amalgam of informal logic, rhetoric, dialectics, AI and related disciplines that study arguments in natural language). In attempting to answer this question, I focus on two aspects of their approach: first, their evolutionary account of reasoning; second, their attempt to use it to explain the persistence of cognitive errors that tend to characterize ordinary reasoning (most notably, in instances of confirmation bias and motivated reasoning).
In making my own arguments, I put aside some concerns about Mercier and Sperber's project that are rooted in the thought that we can reason (i.e., offer reasons for some belief or action) in radically different ways: by constructing geometrical demonstrations, by declaiming, by drawing political cartoons, by thinking to ourselves, by engaging in parliamentary debate, by performing in a play, and so on and so forth (e.g., Birdsell & Groarke, 2007; Carozza, 2007; Gilbert, 1997). This makes reasoning an umbrella concept which is, arguably, ill suited to a general account ("a grand theory") of reasoning built on one its many variants.
But that is a concern I leave for elsewhere. Assuming a general approach, why do humans reason? Mercier and Sperber (2011) answer that reasoning has evolved as an aid to communication: "Reasoning enables people to exchange arguments that, on the whole, make communication more reliable and hence more advantageous" (p. 60). It does so by acting as a mechanism of epistemic vigilance which allows one to evaluate the content of messages we receive (p. 96). "Reasoning contributes to the effectiveness and reliability of communication by allowing communicators to argue for their claim and by allowing addressees to assess these arguments. It thus increases both in quantity and in epistemic quality the information humans are able to share" (p. 60). Mercier and Sperber dub this account the "argumentative" theory of reasoning.
The claim that reasoning is a mechanism for persuading others is in keeping with well-established rhetorical accounts of argument. Mercier and Sperber's unique perspective is their claim that the argumentative theory explains a body of psychological research, which is usually taken to show that humans are poor reasoners. In particular...