Progressives, he shows, have been suckers for a myth of human cognition he labels the Enlightenment model. This holds that people make rational decisions by assessing facts. All that has to be done to persuade people is to lay out the data: they will then use it to decide which options best support their interests and desires.

A host of psychological experiments demonstrates that it doesn't work like this. Instead of performing a rational cost-benefit analysis, we accept information which confirms our identity and values, and reject information that conflicts with them. We mould our thinking around our social identity, protecting it from serious challenge. Confronting people with inconvenient facts is likely only to harden their resistance to change.

Our social identity is shaped by values which psychologists classify as either extrinsic or intrinsic. Extrinsic values concern status and self-advancement. People with a strong set of extrinsic values fixate on how others see them. They cherish financial success, image and fame. Intrinsic values concern relationships with friends, family and community, and self-acceptance. Those who have a strong set of intrinsic values are not dependent on praise or rewards from other people. They have beliefs which transcend their self-interest.