French economist Thomas Piketty's book "Capitalism in the Twenty-First Century" has been inspiring a lot of comment and controversy. The English translation published last month zipped to No. 1 on amazon.com.
It has given a lift to economists on the Left who have cheered on Barack Obama's flagging attempts to make income inequality a voting issue. They have hailed it as "truly superb" and "extraordinarily important."
Others, not all on the Right, have taken a jaundiced view. "All wrong" was the verdict of one. "The main argument is based on two (false) claims," concluded another.
Piketty's title echoes Karl Marx's "Das Kapital," and his argument is similar: returns on capital tend to exceed returns to labor, producing increasing income inequality and concentration of wealth.
That happened in the 19th century, he says, and is likely to happen again in the 21st. The 20th century was a happy exception because of the wealth-destroying effects of two world wars and the Great Depression.
Piketty goes far beyond Obama's tepid responses -- a higher minimum wage, forgiveness of college loans -- to a red-hot remedy: an 80 percent global tax on wealth.
That's obviously not going to happen any time soon. But from the hosannas and harrumphs that have greeted the book -- no, I haven't read all 577 pages -- certain conclusions can be drawn.
There is general agreement that Piketty has compiled an impressive array of data on income inequality in multiple nations going back 200 years or more. There is agreement also that he thoughtfully states caveats and cautions about data interpretation.
His thesis seems at least plausible at a time when the very top incomes have increased much more rapidly than those at the middle and bottom. Even some critics acknowledge that, as the Washington Post's Robert Samuelson writes, "the present concentration of income and wealth feels excessive. It understandably stirs resentment."
But is his picture of current trends complete? The Manhattan Institute's Scott Winship points out that relying, as Piketty does, on tax returns for the U.S. statistics means omitting income from Social Security, food stamps, public housing, Medicare and Medicaid.
Tax returns count roommates and unmarried partners as separate units when they are part of a larger household. They don't include employer-paid health insurance -- an increasing share of employee compensation in recent decades.