Economics, as it is often taught today, portrays us as homo economicus-someone who doesn't vote in presidential elections, doesn't return lost wallets, and doesn't leave tips when dining out of town. Julie Nelson reminds us that most people aren't really like that. She helps point the way to a richer, more descriptive way of thinking about economic life.

When people bump up against one another in the course of pursuing their goals, it is in everyone's interest to resolve any resulting problems in the least costly ways possible.

As John Maynard Keynes taught us in the 1930s, in such situations, government is the only entity with both the motive and the ability to boost total spending by enough to put people back to work. As it happens there are long lists of important public projects that cry out to be done.

In short both the things we feel we need and the things available for us to buy depend largely—beyond some point, almost entirely—on the things that others choose to buy.

If top marginal income tax rates are set too high, they discourage productive economic activity. In the limit, a top marginal income tax rate of 100 percent would mean that taxpayers would gain nothing from working harder or investing more. In contrast, a higher top marginal rate on consumption would actually encourage savings and investment. A top marginal consumption tax rate of 100 percent would simply mean that if a wealthy family spent an extra dollar, it would also owe an additional dollar of tax.

Adam Smith's uncritically enthusiastic modern disciples portray his invisible hand theory as saying that market forces reliably harness selfish individuals to serve the common good. That's often true, but as Darwin recognized clearly, many traits that serve the interests of individual animals make life more difficult for larger groups.

If the search is for examples that contradict the predictions of standard economic models, a good rule of thumb is to start in France.