Jost wanted to find out and, with a group of colleagues, set off to map the psychological infrastructure of politics. They didn’t bother asking people about cap-and-trade or gun control, but focused on jazz, masturbation, and gardening. What they discovered was a series of contrasts: Conservatives approved of documentaries and going to bars; liberals looked favorably upon motorcycles and singing songs. In earlier studies, liberals had been shown to be unpredictable and uncontrolled, conservatives conscientious and trustworthy. Jost found that liberals embraced those considered outside the social mainstream, like lesbians, “street people,” and atheists; conservatives approved of fraternities and sororities, politicians, and Caucasians. Conservatives were fonder of children, liberals of professors. Among women, conservatives were more into sex; among men, Jost and his colleagues found the opposite.

They also visited the rooms of 76 UC-Berkeley students, along with a series of five nearby offices, and coded nearly every item in the rooms after quizzing the spaces’ inhabitants about their attitudes. Conservatives’ bedrooms had more laundry baskets, postage stamps, and sports memorabilia. Liberals had movie tickets and larger collections of CDs and books. Conservatives had calendars, flags, and ironing boards. Liberals had international maps, art supplies, and stationery. Conservative offices were less “stylish” and “comfortable”; liberal workplaces were more colorful. When Jost and his colleagues videotaped three-minute interviews with the students, then reviewed the tapes, the liberals were chattier, the conservatives withdrawn and cautious.

Jost’s goal wasn’t to confirm the cheap ideological caricatures of columnists—although the paper does a magnificent job of it—but to see what people’s not obviously political characteristics might explain about how their minds work. “As a general rule,” the authors wrote, “liberals are more open-minded in their pursuit of creativity, novelty, and diversity, whereas conservatives seek lives that are more orderly, conventional, and better organized.” Rare midlife conversions aside, our parties are groups of two different kinds of people, they said, divided not by class or geography or education but by temperament.