... course, they became conventional wisdom. There was only one problem: they weren’t true. There was another factor, meanwhile, that had greatly contributed to the massive crime drop of the 1990s. ... Most of their theories sounded perfectly logical. It was the roaring 1990s economy, they said, that helped turn back crime. It was the proliferation of gun con-trol laws, they said. It was the ... a single theme, crisply expressed in a sentence or two, and then tell the entire story of that theme: the history of salt; the fragility of democracy; the use and misuse of punctuation. This...