These days, too many things come at a price, argues Michael Sandel, a political philosopher and Harvard professor. Market values have metastasized through our society, he says, distorting debate about issues as complex as health care and immigration and as seemingly simple as the question "What do we value?". In his recent book, What Money Can't Buy: The Moral Limits of Markets, Sandel accuses businesses and the U.S. government of sacrificing values such as justice and respect for human dignity in favor of utility. Leigh Buchanan asked Sandel about when such trade-offs cross the line and what he thinks politicians should be discussing.

What are market values? How are they intruding where they don't belong?
They're a way of valuing goods, based on use. When we're talking about televisions, toasters, and cars, market values are appropriate. But when we're talking about personal relations or family, market values may not be appropriate. For example, even if I wanted more friends, it wouldn't work to try to buy some. The money that would buy the friend dissolves the good that makes friendship valuable. We have drifted from having a market economy to becoming a market society. A market economy is a valuable and effective tool for organizing productive activity. A market society is a place where almost everything is up for sale.

Is there an argument to be made that the ceaseless pressure on companies to innovate propels them into morally questionable areas?
Yes. Advertising is a very good example of this. The intense pressure to capture human attention has pushed it into morally questionable areas. For example, many school districts now are allowing advertising on school buses, in the cafeterias, in classrooms. And the advertising companies promote this to potential clients, saying you can gain access to a captive market of teenagers without the usual distractions. And it's not just schools. The fans that people use in churches have ads on the back. They used to be from funeral homes, but now it's corporations. So the congregation sits fanning itself in one large wave of product placement. Churches, fire trucks, fire hydrants, police cruisers. There's advertising in jail cells. Talk about a captive audience.

The political parties generally frame economic debates around taxes and spending. What should they be talking about?
The values that underlie their views on taxing and spending. Beneath those arguments are questions: What is the relationship between individual rights and the common good? What do we owe one another as citizens? Those are big philosophical issues, and they aren't just abstract ideas for scholars.

What examples would you use to frame such a debate?
Increasingly, we have relied on the market to allocate military service. In Iraq and Afghanistan, there were more paid military contractors on the ground than there were U.S. troops. Yet we never had a public debate about whether we wanted to outsource the war to private companies.

What are the most extreme market solutions you've seen proposed by politicians?
One novel effort to raise funds for local government was put forward by a candidate in Nevada who proposed allowing people to buy permits to speed up to 90 miles an hour. The state highway patrol concluded that it would imperil public safety.

Did that candidate win?