The biological images of humanity represent us as consistently serious: we relentlessly and aggressively further the survival of our genes, and adapt our responses with computer-like regularity to our experience of punishment and reward. Yet we are in fact rather a frivolous species. We have called ourselves not only rational and tool-making (Homo sapiens and faber), but also H. ludens, or gamesman.

We are, however, accustomed to distinguish sharply between work and play; and, according to proverbial lore, all work and no play makes Jill a dull girl. But in practise, as we see below, it is often difficult to decide whether an activity is one or the other. The result has been difficulty not only for biologists but also for economists. Human beings work for food and other necessities, but not only for them. Sometimes they fail to work when, on any simple, rational calculation, they should do so; and, more interesting, sometimes they work without need. One result is that economists' models or images of humanity have limitations strangely similar to the biological images. Economists try to reduce the complexities of human motivation to simple principles; and their stories also resemble the biological images in having political implications. The present chapter continues the account of the discrepancies between simplified accounts of human action and what we actually do; and we begin with those of economists.