an aging green Chevy Cavalier with a dusty dashboard and a window that doesnt quite shut, producing a dull roar at highway speeds. But the car is quiet for now, as are the noontime streets: gas stations, boundless concrete, brick buildings with plywood windows. An elderly homeless man approaches. It says he is homeless right on his sign, which also asks for money. He wears a torn jacket, too heavy for the warm day, and a grimy red baseball cap. The economist doesnt lock his doors or inch the car forward. Nor does he go scrounging for spare change. He just watches, as if through one-way glass. After a while, the homeless man moves along. "He had nice headphones," says the economist, still watching in the rearview mirror. "Well, nicer than the ones I have. Otherwise, it doesnt look like he has many assets." An Explanat ory Not e     Steven Levitt tends to see things differently than the average person. Differently, too, than the average economist. This is either a wonderful trait or a troubling one, depending on how you feel about economists. -The New York Times Magazine, August 3, 2003     In the summer of 2003, The New York Times Magazine sent Stephen J. Dubner, an author and journalist, to write a profile of Steven D. Levitt, a heralded young economist at the University of Chicago. Dubner, who was researching a book about the psychology of money, had lately been interviewing many economists and found that they often spoke English as if it were a fourth or fifth language. Levitt, who had just won the John Bates Clark Medal (awarded every two years to the best American economist under forty), had lately been in- terviewed by many journalists and found that their thinking wasnt very . . . robust, as an economist might say. But Levitt decided that Dubner wasnt a complete idiot. And Dub- ner found that Levitt wasnt a human slide rule. The writer was daz- zled by the inventiveness of the economists work and his knack for