The market system allows individuals to exchange goods and services voluntarily, based on prices, without knowing one another. For instance, the cup of coffee a person drinks in the morning was brought to that person by thousands of strangers, who cultivated, harvested, processed, manufactured, packaged, shipped, stocked, and sold goods at various stages of production along the way.

One way to appreciate the distinctiveness of market-mediated trade among strangers is to contrast it with other ways in which people transact with one another. The anthropologist Alan Fiske (2004) suggests that all interpersonal transactions can be sorted into four relational models:

• In a communal sharing transaction, such as a family dinner, every member in the relationship is entitled to share in what is available.
• In an authority ranking transaction, such as a decision made in a traditional military unit or a corporation, there is a clear hierarchy, with...