These days, some people want to impose a new Buffett tax on millionaires while others are outraged that low income people pay no income taxes at all and still others want to cut taxes on “job creators.” All in the name of fairness. Is the tax code fair? Should it be? It all depends on what you mean by fair, of course, but at an Urban Institute panel this week, two economists, a tax historian, and a philosopher agreed that in many important ways, it very likely is not. Fairness is one of those concepts that makes economists really nervous. Because it is so subjective and impossible to measure, they usually avoid the idea entirely, preferring to stick with what they can count. Still, my Tax Policy Center colleague Gene Steuerle, Brookings Institution economist Belle Sawhill, Tax Analysts historian Joe Thorndike, and Howard University philosophy professor Charles Verharen joined moderator Greg Ip, The Economist’s U.S. economics editor, in tackling the issue. The result was a fascinating look at a complicated issue from some very different perspectives.  It is well worth watching. Gene divided fairness into three categories:  The first, which he calls the king of principles, is equal justice (what economists define as horizontal equity). Are people with equal ability to pay taxed equally? The second is progressivity (vertical equity in econo-speak). Do the better off pay more tax than those who are less well off?   The third is individual equity. Are we entitled to keep the rewards of our own work? Is it unfair if we cannot? To that, one could add a fourth, which Gene and TPCs Rudy Penner have written about extensively. And that is generational equity. For instance, is it fair to burden those not yet born with the bill for the cost of maintaining our standard of living? Verharen argued that fairness, which he defined as love for those most in need  (others may say individual sacrifice for the greater good), is hard-wired in family relationships and in much religious thought—to say nothing of Karl Marx. But, he noted, the concept of fairness has changed dramatically over the centuries. Once, and still in some cultures, killing a sick child to preserve the rest of a family is considered “fair.” In a much less profound way, our concept of tax fairness has also evolved over the past two centuries. Joe Thorndike reminded the audience that for much of U.S. history, people were taxed on what they consumed (mostly through tariffs and excise taxes). But from the Civil War though the late 19^th century, tax fairness was redefined as ability to pay. The result: the rise of the progressive income tax. But, Joe says, the idea was to distribute the tax burden, not to redistribute wealth. And that raises the question about whether today’s tax laws are an effective way to address income inequality. Assuming, of course, that you think it is even a problem.   Much of the current political debate is over Gene’s concept of equal justice. With a tax code larded with $1 trillion in tax preferences aimed at rewarding some taxpayers and punishing others, we are far from a system where people with equal incomes are taxed equally. As Greg asked, if this concept is so important, why do we do it so badly? And that raises yet another interesting question: Fair relative to what? Why do we presume that the current distribution of taxes is the right one, and thus judge proposals not on their own merits but compared to what we do today?   Finally, Belle and other panelists warned that it is dangerous to think about the tax code in isolation. Shouldn’t a measure of fairness also consider who benefits from direct government spending, as well as that $1 trillion in tax preferences? It probably should. That is, once we decide what we mean by fairness in the first place.