"Why do people behave the way they do? Mainly because of their interests," says Richard Swedberg, professor of sociology at Cornell University, whose book "Interest" (Open University Press) has just been published.

Although for 150 years or so economists have been explaining people's behavior through their interest in making money, Swedberg argues that people's interests are not all related to money.

"It is true that [this type of] interest helps explain a lot of behavior that otherwise would not be explicable. But interests drive people also in political, religious, spiritual and sexual areas," said Swedberg, an economic sociologist and associate director at the Center for the Study of Economy and Society. In what is the first book in the English language on the concept of interest, Swedberg writes that these other kinds of interest are sometimes much more powerful types of interest than economic interest.

The 128-page paperback is largely an intellectual history of interest -- tracing the origin of the word from the Middle Ages and its early use in philosophy, political science, literature and everyday language to its emergence as a sociological idea that began to develop in the late 1800s. In the 1840s, John Stuart Mill wrote that economics can only become a science if it is based on the assumption that what drives people is a desire for wealth. But this type of argument, according to Swedberg, led to a much too narrow view of the concept of interest. He also reviews how sociologists have tried to incorporate the concept of interest into their various theories and discusses how the concept is used today in modern political science and economics.

In the final chapter, Swedberg discusses how the idea of interest can be used as a policy tool to change social reality, such as regards the U.S. Constitution, which tries to balance various interests against each other and in this way creates a political system that makes it hard to abuse power.

Swedberg concludes his treatise on interest with an in-depth discussion of conflict-of-interest legislation to show how the idea of interest can be used as a policy tool.