In the 1930s, a famous American psychologist was quoted as saying that he didn’t understand why people were interested in motivation when it was so obvious that money was the source of all incentive. His opinion has the ring of truth, it is generally supported by experience, and it has the pragmatic directness that makes much sense in a culture based on pragmatic assumptions. No wonder most people would agree that the long and the short of the matter is that men and women will or won’t do things depending on the money-or other extrinsic rewards or punishments-they get. Our social institutions, from nursery schools to jobs, are built on this belief. It is also the assumption underlying the main psychological theories currently in use.