Faced with any choice, especially big ones, we use our rational minds to identify reasons for and against, test them if possible, then do what seems most sensible. We know we're not infallible: numerous biases lead us astray, and we're horribly prone to rationalisation – that is, misusing our reasoning faculties to corral our emotions into line. But these are exceptions, we tell ourselves. After all, we're rational beings. That's what separates us from horses, or sardines, or Jeremy Clarkson.
Yet a forthcoming paper by the cognitive scientist Dan Sperber and the philosopher Hugo Mercier, "Why Do Humans Reason?", proposes a radical alternative. What if we evolved the capacity to reason not to get closer to the truth, but to persuade others (and ourselves) of viewpoints, regardless of their relation to truth? In evolutionary terms, the survival benefits of such a talent are obvious. Maybe – to borrow the analogy used by Jonah Lehrer, who highlighted the paper on his blog at wired.com/wiredscience – we don't go about life as quasi-scientists, as we flatter ourselves, but as quasi-talk radio hosts, devoting our reasoning energies to concocting arguments that feel persuasive.
This is speculation, but Sperber and Mercier show it makes sense of countless psychological quirks that otherwise seem mysterious. Lehrer cites the famous study in which people were asked to rate five jams previously rated by food experts. Non-experts ranked them the same as experts – except those who were asked to provide reasons, who diverged hugely, preferring jams that (according to expert opinion) were worse. Seemingly, they were casting about for convincing-sounding reasons – "Smoother jam is better", say – which threw them from their instinctive preference for the jams everyone else agreed were best. If reasoning is about truth-finding, this is bewildering, but if it's about generating fuel for persuasion, it makes sense. Rationalisation, from this perspective, isn't a failure of reasoning. It's what reasoning's for. . . .