Know your enemy, they say. Jonathan Haidt might rephrase this as: understand your enemy. Know his moral instincts and the way he reasons through an argument. See his point of view; be his friend. Haidt is not a Christian evangelist but a Jewish east-coaster, social psychologist and author of the latest political it-book, The Righteous Mind: Why Good People are Divided by Politics and Religion (Allen Lane). He’s already talking to the White House and if you notice an elegant shift in Ed Miliband’s rhetoric from wonkish to spiritual, you’ll know who to credit.

The book, says Haidt in the lobby of a grand hotel in Westminster, is designed for liberals (in the US sense) who think conservatives are evil and stupid and if only they understood the data better, they’d get it. It won’t make comfortable reading if you fall into that category. Haidt wants you to be more like them.

And if you’re a politician, you need to learn how to talk like them. His advice: “Understand the moral foundations, and commit less sacrilege.” To translate: understand, for example, why someone might be pro-life and try not to stamp all over that deeply felt moral position.

Most of us, he argues, have a set of moral values that have filtered from our heritable genes and the influence of our peers. (He has me taped: “Do you like to try new foods? Do you see the world as a dangerous, threatening place? . . . You have a liberal brain.”) There are, he says, six key moral bases: care/harm, fairness/cheating, loyalty/betrayal, authority/subversion, sanctity/degradation and liberty/oppression.

In good faith

Conservatives in the US, in their devotion to flag and faith, appeal to a wider range of moral bases than liberals, who tend to emphasise only three: care, fairness and liberty. They also realise that: “Politics is much more like religion than it is shopping. The Republicans have a religion, they know what America is, what they stand for. The Democrats, what do they stand for? They don’t know.”

Haidt wants to do more than shake up the liberal agenda: he also wants to civilise the vicious US political culture. The extreme polarisation of US politics is a relatively recent phenomenon, he says, dating back to the culture wars of the 1960s and entrenched by Newt Gingrich’s decision as speaker of the house in 1995 to let Republican senators live with their families in their home states, rather than in Washington. Gone were the late-night drinks and bipartisan friendships. Their division prefigured that of the people – “lifestyle enclaves” mean that Americans living in Williamsburg or Wasilla will rarely encounter someone from a different political leaning.

So, befriend a conservative. They are in your midst, says Haidt, but are “in the closet. And they’re in the closet because there is such hostility they can’t come out. This is the situation in social sciences.” In all his years in academe, he has dug out one lonely conservative working in his field. Haidt, once a diehard liberal, now a proud “centrist”, smiles: “I know him. He’s a friend of mine.”