But redistribution alone will not be enough to address the inequality challenge of the 21st century. All societies that have successfully tamed inequality have done so mostly by curbing the concentration of pretax income — the inequality generated by the markets — for the simple reason that extreme market inequality undermines the very possibility of redistribution. Tolerating extreme inequality means accepting that it’s not a gross policy failure, not a serious danger to our democratic and meritocratic ideals — but that it’s fair and just and natural. It produces its own self-justifying ideology. It vindicates the “winners” of world markets. But vindicated winners, sure of their own legitimacy, seldom share much of their “just deserts” with the rest of society.

An extreme concentration of wealth means an extreme concentration of economic and political power. Although many policies can help address it, progressive income taxation is the fairest and most potent of them all, because it restrains all exorbitant incomes equally, whether they derive from exploiting monopoly power, new financial products, sheer luck or anything else.

A common objection to elevated top marginal income tax rates is that they hurt economic growth. But let’s look at the empirical evidence. The United States grew more strongly — and much more equitably — from 1946 to 1980 than it has ever since. But maybe in those years the United States, as the hegemon of the post-World War II decades, could afford “bad” tax policy? Let’s look then at Japan in 1945, a poor and war-devastated country. The United States, which occupied Japan after the war, imposed democracy and a top marginal tax rate of 85 percent on it (almost the same rate as at home — 86 percent in 1947). The goal was obviously not to generate much revenue. It was to prevent, from that tabula rasa, the formation of a new oligarchy. This policy was applied for decades: In 1982, the top rate was still 75 percent. Yet between 1950 and 1982, Japan grew at one of the fastest rates ever recorded (5.1 percent a year per adult on average), one of the most striking economic success stories of all time.

Contrast Japan in 1945 with Russia in 1991. When Communism fell, Russia was also a poor country, with income and life expectancy well below that of Western economies. In lieu of 85 percent top rates, however, Russians got fast privatization and a top tax rate of 30 percent — again modeled on what was prevailing in the United States at the time (31 percent in 1991). That rate was replaced in 2001 by an even lower flat rate of 13 percent. That shock therapy created a new oligarchy, led to negative income growth for the bottom half of the population, fostered a general discontent with democracy and produced a drift toward authoritarianism.

Progressive income taxation cannot solve all our injustices. But if history is any guide, it can help stir the country in the right direction, closer to Japan and farther from Putin’s Russia. Democracy or plutocracy: That is, fundamentally, what top tax rates are about.

Emmanuel Saez and Gabriel Zucman are professors of economics at the University of California, Berkeley, and the authors of a forthcoming book about tax justice.

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