Why do humans reason? Many animals draw inferences, but reasoning—the tendency to produce and respond to reason-giving performances—is biologically unusual, and demands evolutionary explanation. Mercier and Sperber (Behav Brain Sci 34:57–111, 2011) advance our understanding of reason’s adaptive function with their argumentative theory of reason (ATR). On this account, the “function of reason is argumentative… to devise and evaluate arguments intended to persuade.” ATR, they argue, helps to explain several well-known cognitive biases. In this paper, I develop a neighboring hypothesis called the intention alignment model (IAM) and contrast it with ATR. I conjecture that reasoning evolved primarily because it helped social hominins more readily and fully align their intentions. We use reasons to advance various proximal ends, but in the main, we do it to overwrite the beliefs and desires of others: to get others to think like us. Reason afforded our ancestors a powerful way to build and maintain the shared outlooks necessary for a highly collaborative existence. Yes, we sometimes argue so as to gain argumentative advantage over others, or otherwise advantage ourselves at the expense of those we argue with, but more often, we reason in ways that are mutually advantageous. In fact, there are excellent reasons for thinking this must be so. IAM, I suggest, neatly explains the available evidence, while also providing a more coherent account of reason’s origins.

A bit over five years ago I wrote a blog post on Hugo Mercier and Dan Sperber’s then-recently published paper on their argumentative theory of reasoning. At that point I was about to start a research project on deductive reasoning, having as my main hypothesis the idea that deductive reasoning is best understood from a dialogical – and thus, argumentative – perspective, and so naturally the argumentative theory of reasoning was something to pay attention to. Yesterday was officially the very last day of my research project, and fittingly, earlier this week we convened for the very last (official) reading group session of the project to discuss a very recent paper by Andy Norman (CMU), forthcoming in Biology and Philosophy: , ‘Why we reason: intention-alignment and the genesis of human rationality’ . The paper presents a broadly evolutionary account of human reasoning faculties, which takes on board much of Mercier & Sperber's (M&S) argumentative theory, but modifying it in important respects. Here is the abstract:

Norman’s paper does a good job at problematizing some of the aspects of M&S’s account that I found less compelling – indeed, two of them are briefly discussed in my blog post of five years ago, namely that M&S reduce reasoning to inherently linguistic experiences, and that they do not emphasize enough the cooperative components of these practices.* Norman’s account, by contrast, addresses both issues in ways that are to my mind quite compelling, and which I will discuss in more detail shortly

Perhaps the first thing to notice is that Norman adopts a rather specific notion of reasoning, pertaining exclusively to reason-giving (presumably public) performances, which he contrasts with inference-drawing operations – presumably, what Chrysippus’ dog does when it immediately launches onto the right side of a forking path after sniffing on the left side and not smelling the scent of its prey (see here for a paper by M. Rescorla on why this is best not seen as an instance of non-linguistic deductive reasoning). Now, as some readers may recall, the practice of exchanging reasons is very much on my mind at the moment (see this recent blog post). Norman’s account of this practice as primarily aimed at “overwrit[ing] the beliefs and desires of others: to get others to think like us” is indeed in the ballpark of the idea that exchanging reasons through argumentation is primarily aimed at sharing information, or transferring epistemic assets, which I hope to develop in my next research project. (See here for an earlier blog post on argumentation as gift-exchange.) Norman’s formulation above suggests something more coercive (“to get others to think like us”) than the model he then actually goes on to develop in his paper, especially given his emphasis on reasoning “in ways that are mutually advantageous”.

The proposal fits right in within the recent surge in popularity of approaches to human cognition that emphasize culture and socialibility; to name but a few recent books going in this direction: Paul L. Harris’ Trusting what you’re told; Kim Sterelny’s The Evolved Apprentice; Joseph Henrich’s The Secret of our Success. Obviously, it is not a new idea, but it has arguably accrued in popularity in the last ten years or so. On Norman’s IAM, exchanging reasons is a “biotechnology for mind-writing”, which conferred evolutionary advantages to those mastering it because it enhanced social coordination through the alignment of intentions. He also recognizes that aligning intentions that also happen to be truthful may confer even more advantages, but his emphasis is not on the truth-conduciveness component of reasoning. Instead, the focus is on the social component: “the ‘‘technology’’ of reason—verbal mind-writing, if you will—ushered in a unique and distinctively human form of ultrasociality.”

As I mentioned above, the IAM proposal has two attractive features which pertain precisely to some of my main concerns regarding M&S’s argumentative theory. Firstly, it does not construe reason-exchanging as an intrinsically linguistic process; indeed, the ‘ur-situation’ that Norman describes of a hominid group hunting for mammoth and being convinced to continue along the river by one of its members who points (non-verbally) at a mammoth footstep is supposed to illustrate how reasons can be given non-verbally, i.e. through gestures. Here Norman draws on the work of M. Tomasello and others, who have emphasized the primacy (both from a phylogenetic and from an ontogenetic perspective) of gestural language over verbal language. On this scenario, reason-giving in rudimentary form does not presuppose verbal language, and in fact perhaps the pressure to come to more efficient ways to exchange reasons will have led (among other reasons) to the emergence of verbal language.

Secondly, Norman emphasizes the idea of reasoning in ways that are mutually advantageous. The apparent focus on ‘manipulative’ and ‘selfish’ modes of reasoning in M&S’s proposal was one of its most polemic features (see the NYT piece reporting on one such reaction). Even if this is a misinterpretation of the proposal, a point that Norman makes quite eloquently (p. 10) is that M&S do not seem to take sufficiently into account what’s in it for the receiver of reasons to stick around and pay attention to the reason-giver. In contrast, on Norman’s model, the exchange of reasons is mutually advantageous, in particular insofar as intention alignment is advantageous not only for the group but for the individuals in question, reason-givers and reason-receivers alike. Indeed, even though he does not use this exact terminology, I think the model further supports the idea of reasoning as a process of sharing epistemic assets; the reason-receiver in fact gains something valuable rather than merely being ‘manipulated’ to her disadvantage.

There is however one aspect of Norman’s account which I find unconvincing so far, namely his suggestion that the reason-giver does not need to have the intention to engage in mind-writing for a particular episode to count as an instance of reasoning: “Strictly speaking, the reason-giver needn’t intend to change the reason-taker’s mind” (p. 9). This seems problematic in that, all of a sudden, too much seems to count as reasoning. If my daughter coughs a lot in the middle of the night while asleep, this may count as a reason for me to take her to the doctor the next day for an examination, but it seems odd to say that a process of reasoning takes place. I’d prefer to say that reason-giving must be an intentional process, but I acknowledge that spelling out what exactly this means is by no means obvious.

But all in all, the members of my research group and I found Norman’s paper to be very stimulating, and for me in particular it provides several interesting elements now that I am in the process of writing a new grant proposal precisely on the topic of reasoning in the social sense of exchanging reasons. Five years after having written about the M&S paper just before starting my deduction project, my interests have not changed that much it seems, but clearly there is still much to be learned and explored on these matters.

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* In an exchange with me over at Facebook, Mercier suggests that both Norman and I seem to underestimate the extent to which cooperation is in fact emphasized in his and Sperber’s theory. To be honest I haven’t yet had the time to go back to the original M&S paper to see for myself whether I had gotten the wrong impression back then.