One of his key insights is that we are much less rational than we think we are. We tend to make moral judgments intuitively and immediately. If asked, we can produce reasons for our judgments, and might even believe that’s why we made our decisions — but, in reality, these are just rationalizations for our intuitive hunches.

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When Haidt looks at American politics, he doesn’t see a free-flowing, open-minded exchange of ideas. Instead, he sees a conflict between two profoundly different moral mind-sets--a conservative mind-set and a liberal one--that dictate where people stand on issues, and are unlikely to change.

Republicans and Democrats do have intuitions in common: the intuitions that fairness is a moral good, and that doing harm is a moral wrong. But, by asking thousands of people to take surveys and ponder moral dilemmas, Haidt — who identifies as a liberal — has found that conservatives live in a broader moral universe. To a much greater degree than liberals, they draw on moral intuitions about loyalty, tradition, authority, and sanctity. That difference explains why Republicans are more concerned than Democrats about patriotism and family values. And, in their moral breadth, Haidt has found, Republicans are more typical of people around the world; the more tightly focused morality of liberals is rarer.

Ultimately, Haidt argues, the differences between liberals and conservatives are both natural and inevitable. The rancor between the groups, he argues, comes from something else: a human tendency toward groupish self-righteousness that takes over, obscuring the ways in which our own beliefs are irrational, and making it all too easy to demonize people who see the world through a different moral lens. “Human nature,” Haidt writes, “is not just intrinsically moral, it’s also intrinsically moralistic, critical, and judgmental.”