I have come to think of this idea as Piketty’s First Law of Inequality. The fact that the rich earn enough money to save money allows them to make investments that other people simply cannot afford. And investments — whether stones, land, corporate stock or education — tend to bring a positive return. Piketty describes the relationship formally as r > g: the rate of return on capital usually exceeds economic growth.

Piketty, however, notes that certain things can disrupt this relationship. When a war destroys farms, the big farmers are no longer much richer than anyone else. A depression can play the same role. When income or wealth is taxed at high rates, the rich are not able to save and accumulate as much. It’s no accident that in the decades after World War II, when middle-class incomes were rising even more rapidly than the incomes of the rich, the top marginal income-tax rates were exceptionally high. In the 1950s, the top rate exceeded 90 percent. Today, it is 39.6 percent, and only because President Obama finally won a yearslong battle with Republicans in early 2013 to increase it from 35 percent.

Piketty advocates a global wealth tax aimed more directly at capital inequality than income taxes currently are. It would apply to anyone with more than about $1.4 million in net worth and become steeper on higher fortunes than moderate ones. It’s an interesting idea, but it has little, if any, chance of passing the current legislative environment. Yet Piketty mentions another, more politically plausible force that can disrupt his first law of inequality: education. When a society becomes more educated, many of its less-wealthy citizens quickly acquire an ephemeral but nonetheless crucial form of capital — knowledge — that can bring enormous returns. They learn to make objects and accomplish tasks more efficiently, and they sometimes create entirely new objects (or services). They become those children in the small village who attended school, went off to work in a factory, became managers and made bigger economic leaps above their parents than those of the large farmer did.

The great income gains for the American middle class and poor in the mid-to-late 20th century came after this country made high school universal and turned itself into the most educated nation in the world. As the economists Claudia Goldin and Lawrence Katz have written, “The 20th century was the American century because it was the human-capital century.” Education continues to pay today, despite the scare stories to the contrary. The pay gap between college graduates and everyone else in this country is near its all-time high. The countries that have done a better job increasing their educational attainment, like Canada and Sweden, have also seen bigger broad-based income gains than the United States.

Yet the debate over our schools and colleges tends to exist in a separate political universe from our debate over inequality. Liberals often shy away from making the connection because they worry it holds the struggling middle class and poor responsible for their plight and distracts from income redistribution. Many conservatives fear the implicit government spending involved. And so, our once-large international lead in educational attainment has vanished, and our lead in inequality has grown.

There are some reasons for optimism in education. Charter schools and school systems that have tried to introduce more accountability offer some lessons about what works and doesn’t in K-12. The total number of college graduates has begun rising again. That said, the changes in education — not to mention the tax code — are not nearly large enough to counteract the forces pushing in the other direction. A true attack on inequality would require that the country move the issue to the center of every political debate: how we tax wealth, how we tax the income of the middle class and poor (often stealthily through the payroll tax), how we finance schools and measure their results, how we tolerate income-sapping waste in health care, how we build roads, transit systems and broadband networks. These are precisely the sort of policies pursued by countries with better recent middle-class income growth than the United States.

The closest thing to an antihero in Piketty’s book is an economist named Simon Kuznets, who argued in the decades after World War II that inequality was destined to decline. His soothing prediction grew out the experience of the previous few decades, but he and many others confused a trend with destiny. We are now making that same mistake in the opposite direction. Rising inequality is a trend, but it is one we have helped create and one we can still change.