Mercier and Sperber in a recent paper (citation) explain their theory that the function of reasoning is primarily successful group argument. They start with a careful definition of reasoning which is itself very interesting. Stripped to its basics, all inference is made by unconscious mechanisms so we cannot consciously know the way these inferences are made; and, when we need or want reasons for our inferences, the reasons are themselves unconsciously made inferences. ‘Reasoning’ is a special process where plausible reasons are produced for holding some opinion and where reasons are evaluated for how well they support an opinion. Thus the reasons that are produced by reasoning may or may not be similar to whatever ideas causally were used unconsciously to reach an opinion. At this point it is reasonable to ask why we have a mechanism for producing reasons for an intuition which may or may not have anything to do with the actual intuition.

Mercier and Sperber used the concept of function to look at this question  what is the function of reasoning? How does the ability to reason enhance the evolutionary fitness of humans? If there are more than one function, which has been predominant in evolution. They take trouble to avoid ‘just so stories’ and make concrete predictions for their theory.

The default function that has been accepted since the ancient Greeks is that the main function of reasoning is to enhance individual cognition. Another function that has been discussed in the past is that it helps to deal with novelty and anticipate the future. Their function (Argumentative Theory) is that reasoning enables people to exchange arguments that, on the whole, make communication more reliable and hence more advantageous, increasing fitness. They see reasoning as involved in social communication not individual thinking. (Although they take some time explaining what are valid and invalid evolutionary theories, they do not address, at least in this paper, the question of individual and group selection. Some ideas they use could be interpreted as either type of selection and if they wanted a group interpretation they would have needed to justify it as group selection which is not universally accepted.)

As has been featured in the Babel’s Dawn blog many times, the key to the origin of human speech is trust. Apes could probably have evolved speech if they could only trust one another enough to make communication safe. Mercier and Sperber say:

For communication to be stable, it has to benefit both senders and receivers; otherwise they would stop sending or stop receiving, putting an end to communication itself. But stability is often threatened by dishonest senders who may gain by manipulating receivers and inflicting too high of a cost on them. Is there a way to ensure that communication is honest?… To avoid being victims of misinformation, receivers must therefore exercise some degree of what may be called epistemic vigilance. The task of epistemic vigilance is to evaluate communicator and the content of their messages in order to filter communicated information. The interpretation of communicated information involves activating a context of previously held beliefs and trying to integrate the new with old information. This process may bring to the fore incoherencies between old and newly communicated information. When it uncovers some incoherence, an epistemically vigilant addressee must choose between two alternatives. The simplest is to reject communicated information, thus avoiding any risk of being misled. This may, however, deprive the addressee of valuable information and of the opportunity to correct or update earlier beliefs. The second, more elaborate, alternative consists in associating coherence checking and trust calibration and allowing for a finer-grained process of belief revision. In particular, if a highly trusted individual tells us something that is incoherent with our previous beliefs, some revision is unavoidable: We must revise either our confidence of the source or our previous beliefs. We are likely to choose the revision that reestablishes coherence at the lesser cost, and this will often consist in accepting the information communicated and revising our beliefs. But what if the communicator is not in a position to boost her own authority? Another option is to try to convince her addressee by offering premises the addressee already believes or is willing to accept on trust, and showing that, once these premises are accepted, it would be less coherent to reject the conclusion than to accept it. This option consists in producing arguments for ones claims and in encouraging the addressee to examine, evaluate, and accept these arguments. Producing and evaluating arguments is, of course, a use of reasoning. 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.

Now many will think that communication and argument is a small advantage compared to individual thought. Think of the moon landing and the more than 50 millennium of group argument and cooperation that built the skills and knowledge needed for great human accomplishments like it. Cooperation is an enormous advantage and next to impossible without means of establishing trust. Without safe, efficient, effective group communication we would have culture on the level of chimps.

Mercier and Sperber go on to give reasons why reasoning is not all that good at individual thought and very good at group argument. I found them fairly convincing. The paper is rich in references to experiments by many groups that support their case and worth reading  really an interesting paper.

Their conclusion:

Human reasoning is not a profoundly flawed general mechanism; it is a remarkably efficient specialized device adapted to a certain type of social and cognitive interaction at which it excels. There is an asymmetry between the production of arguments, which involves an intrinsic bias in favor of the opinions or decisions of the arguer whether they are sound or not, and the evaluation of arguments, which aims at distinguishing good arguments from bad ones and hence genuine information from misinformation. People are good at assessing arguments and are quite able to do so in an unbiased way, provided they have no particular axe to grind. In group reasoning experiments where participants share an interest in discovering the right answer, it has been shown that truth wins. In group tasks, individual participants come up with and propose to the group the same inappropriate answers that they come up with in individual testing. The group success is due to, first and foremost, the filtering of a variety of solutions achieved through evaluation. When different answers are initially proposed and all of them are incorrect, then all of them are likely to be rejected, and wholly or partly new hypotheses are likely to be proposed and filtered in turn, thus explaining how groups may do better than any of their individual members.

Individuals thinking on their own without benefiting from the input of others can assess only their own hypotheses. Individuals may develop some limited ability to distance themselves from their own opinion, to consider alternatives and thereby become more objective. Presumable this is what the 10% or so of people who pass the standard Wason selection task do. But this is an acquired skill and involves exercising some imperfect control over a natural disposition that spontaneously pulls in a different direction. The great achievements of human thought are collective and result from interactions over many generations. The whole scientific enterprise has always been structured around groups, moral achievements (abolition of slavery) are the outcome of intense public arguments. In group settings, reasoning biases can become a positive force and contribute to a kind of division of cognitive labour. In most discussions, rather than looking for flaws in our own arguments, it is easier to let the other person find them and only then adjust our arguments, if necessary.

I have noticed over my life that what is really important tends done in groups and orally: classroom teaching, legal trials, legislation, worship, pep talks etc. I thought that the main reason for this was the nature of oral language as opposed to written. After reading this paper I would add the value of group reasoning in establishing trust, agreement and best solutions.

Mercier, H., & Sperber, D. (2011). Why do humans reason? Arguments for an argumentative theory Behavioral and Brain Sciences, 34 (02), 57-74 DOI: 10.1017/s0140525x10000968