Is my side
the right side?

We might believe that reason can guide us towards knowledge and wisdom – but when we use it to examine our own thoughts it actually tends to steer us down the wrong paths. So what is it really for?

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What is reason? What is it for? Philosophers since Aristotle have taken for granted that reason is a mental power that separates us humans from other animals and that steers us towards deeper knowledge and wiser decisions. Psychologists, however, have shown that this power doesn’t function as philosophers thought it should.

Consider a simple reasoning problem. A tea and a biscuit cost £1.10 together. The tea costs £1 more than the biscuit. How much does the biscuit cost? Too easy: the biscuit must cost 10p! Or so most people think. This, however, cannot be the right answer. If it were, the tea would cost £1.10 and the tea and biscuit together £1.20. We have to give up our first intuition to reach the correct answer: the biscuit costs 5p and the tea £1.05.

Psychologists, notably the Nobel Prize winner Daniel Kahneman, have devoted much attention to problems such as this one and argued that reason helps us overcome faulty intuitions – for instance the intuition that the biscuit costs 10p. Experimental evidence, however, shows that most people use reason not to correct their mistaken intuitions but to find bad arguments that seem to justify these intuitions.

Psychologists call this bias in favour of one’s initial opinion the “confirmation bias” or “myside bias”. The myside bias is this overwhelming tendency to find reasons supporting one’s initial beliefs rather than to examine them objectively and pay attention to reasons that might undermine them.

Reasoning typically fails to dispel our faulty intuitions and, in so doing, to guide us towards knowledge and wisdom. In fact, it tends to do the exact opposite. By providing us with reasons that support our initial hunches, it makes us more confident that we’re right even when we are wrong. Why would reason behave this way?

Most people use reason to find bad arguments that justify their intuitions

The existence of the confirmation or myside bias is hardly contested. Indeed, scholars seem to have so taken it for granted that they forgot how puzzling it should be. Of course, we should not be surprised to find that evolved adaptations are imperfect and that they sometimes malfunction. What we should find surprising, on the other hand, is to find an adaptation that, like a square wheel, has features that compromise its effectiveness in a systematic rather than accidental way. In our new book The Enigma of Reason, myself and Dan Sperber suggest that to make sense of the myside bias – and of many other puzzling features of reason – we must radically rethink reason itself: what is its function, how it works and why it should have evolved only among us humans.

Contrary to common ideas on the matter, reason, we argue, didn’t evolve to enhance our ability to form beliefs and make decisions on our own. Its function, rather, is social. We humans have a social life that is more intense and much more diversified than any other animal. Successful management of this social life involves both being able to influence others and to sometimes accept, sometimes reject, the influence others might have on us. Reason, we suggest, evolved to produce justifications and arguments in order to influence others and also in order to evaluate, before accepting or rejecting them, the justifications and arguments offered by others to influence us.

Imagine how difficult even the most mundane interactions would be if we couldn’t exchange justifications and arguments. We would constantly run the risk of misjudging others and of being misjudged, of being wrongly disbelieved or of wrongly disbelieving others. Authority could never be contested but only defeated by force. Rights could never be recognised or, for that matter, understood. We need reason not only for grand goals as in science, philosophy or law, but also in our daily social interactions – to justify, for instance, being late at an appointment, to accept or reject other people’s justifications when they are late, to try to convince our spouse to stay at home, to recognise the aptness of the arguments that he or she gives us to go out, rather, and take the children to the beach.

Seeing reason as a tool for social interaction makes sense of its otherwise puzzling features. The myside bias is a case in point. When reason produces justifications and arguments to convince others, a myside bias is obviously functional. If you were impartial and suggested to people reasons to see your actions as unjustified, or if you gave arguments against your own opinions, you would be like a lawyer arguing against her client – except that you would be both the lawyer and the client in this case. If we are right, then the myside bias is a useful feature that helps it fulfil its social function, it is not a “bug”.

In producing justifications and arguments, reason is and should be biased. When, on the other hand, reason evaluates other people’s justifications and arguments, it should be more objective and demanding. Demanding so that we are not swayed by poor reasons, but also objective so that good reasons help us recognise our mistake and change our minds. As we show, there is growing evidence that indeed reason is more objective in evaluating the arguments of others than in producing our own. For instance, when people who are firmly convinced that “the biscuit costs 10p” discuss with people who have figured out that the correct answer is 5p, arguments in favour of the correct solution win. People who had produced bad arguments with conviction recognise that the other side’s argument are better and change their mind without fail. In reasoning on our own, we tend to just confirm and, if anything, strengthen our previous ideas, whether they are right or wrong. In a sincere discussion, people who start with different ideas but with a common goal tend to converge on greater knowledge or greater wisdom.

As we show in our book, this pattern of poor solitary performance and solid group performance is very robust. It is found in young children and in geniuses, in modern universities and small-scale societies, in scientific lab meetings and political forums. Open-minded debate with others is a better way to test and improve our ideas than typically self-serving solitary reflection, which is not what reason is for.

The Enigma of Reason: A New Theory of Human Understanding by Hugo Mercier and Dan Sperber is out now, published by Allen Lane (£25)

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