intellectual overextension is often found in economics, as Gary Saul Morson and Morton Schapiro explain in their wonderful book “Cents and Sensibility: What Economics Can Learn from the Humanities” (Princeton). Morson and Schapiro—one a literary scholar and the other an economist—draw on the distinction between hedgehogs and foxes made by Isaiah Berlin in a famous essay from the nineteen-fifties, invoking an ancient Greek fragment: “The fox knows many things, but the hedgehog one big thing.” Economists tend to be hedgehogs, forever on the search for a single, unifying explanation of complex phenomena. They love to look at a huge, complicated mass of human behavior and reduce it to an equation: the supply-and-demand curves; the Phillips curve, which links unemployment and inflation; or mb=mc, which links a marginal benefit to a marginal cost—meaning that the fourth slice of pizza is worth less to you than the first. These are powerful tools, which can be taken too far. Morson and Schapiro cite the example of Gary Becker, the Nobel laureate in economics in 1992. Becker is a hero to many in the field, but, for all the originality of his thinking, to outsiders he can stand for intellectual overconfidence. He thought that “the economic approach is a comprehensive one that is applicable to all human behavior.” Not some, not most—all