Income inequality has long been a bugaboo of the left. There is just something wrong, liberals think, with X earning much more than Y. They never explain why it’s wrong, of course, apparently regarding it as self-evident. What it is, actually, is a modern echo of the medieval notion of the “just price,” the idea that everything has a proper price for which it should be bought or sold and the authorities (the Church in the Middle Ages, the federal government today) should see that everything is.

In the early Clinton era, Democrats passed and the president signed a bill limiting the deductibility of executive salaries over $1 million from corporate income taxes. Naturally, they didn’t limit the deductibility of the enormous incomes of their Hollywood pals, but intellectual consistency is seldom a political virtue.

The level of inequality diminished, briefly, during the financial crisis of 2008, as stock prices crashed and dividends were cut. But it is now increasing again, as CBS news reported recently. Some economists recommend a top income tax rate of 73 percent in order to foster more equality. But this fails to take into account the ample evidence that as income-tax rates rise, so does tax avoidance.

Others argue that income inequality and growth are inextricably linked and trying to limit one will, necessarily, limit the other.

Still others argue, what income inequality? They say it is mostly a statistical illusion that results from how the “poverty rate” is determined and how income is measured. For instance, the CBO counts realized capital gains as income but not unrealized capital gains. So if two people buy houses the same year for the same price and one sells his 30 years later for a gain of $500,000, he’s in the one percent, but his neighbor who didn’t sell is not. Next year, of course, the seller will be back among the hoi polloi.

And transfer payments, such as Social Security, Medicare, and food stamps, are not counted as income by the CBO in determining the poverty rate. So an elderly couple might be considered below the poverty line, despite receiving a check for $1,700 every month from the government and having most of their medical bills picked up. The elderly couple regard the $1,700 as income (it buys stuff, after all), so why shouldn’t the CBO count it as income?

As so often, statistics are being wielded as political weapons, not as a means to understanding the human universe. And meanwhile, the real measure of prosperity—consumption—is often ignored. For instance, while “wages,” as defined by the Bureau of Labor Statistics, have been relatively flat since the 1980s, consumption by the less affluent has increased briskly. In 2001, only 19.8 percent of low-income households owned a computer. By 2009, it was 47.7 percent. In 2001 21.9 percent of these families had living space of more than six rooms (not counting bathrooms), by 2009 that had risen to 30 percent.

Meanwhile, the No. 1 tool that politicians use to play politics with income inequality, the income tax, turned 100 last Friday. How much has it been used for political purposes? As John Fund points out, in 1913, the tax code was 400 pages long. Today it is 73,954 pages long.