This is a guest post by DePaul political scientist David Lay Williams. He is the author of “Rousseau’s Platonic Enlightenment” and “Rousseau’s ‘Social Contract’: An Introduction.”

President Obama has recently called economic inequality “the defining challenge of our time,” and has devoted significant elements of his proposed budget to meeting it. Other Democrats, such as Elizabeth Warren and Bernie Sanders, have made addressing inequality even more central to their policy agendas. In their own way, some Republicans, such as Marco Rubio, have likewise begun to acknowledge inequality as a serious problem. And, of course, Pope Francis has made international headlines with his denunciations of economic inequality and of the engines of inequality that he sees in the global economic system.

The data confirm that inequality is great and growing. In 1974, the wealthiest 1 percent of Americans earned 8 percent of the nation’s income. By 2007, that figure was nearly 24 percent. Between 1979 and 2005, the wealthiest 0.1 percent of Americans have enjoyed 20 percent of all income gains. The poorest 60 percent have seen merely a 13.5 percent share of the same pie. As of 2009, the wealthiest 1 percent of Americans had as much as the poorest 50 percent. Emmanuel Saez at the University of California, Berkeley has recently found that income inequality in the United States has reached a level last seen in the 1920s. And the trend expressed by these figures seems to be accelerating.

But why is this a problem? Isn’t the promise of wealth what spurs the poor to improve their lot, and, in doing so, the general welfare? And even if the poor are to be pitied, shouldn’t we fear policy aimed at lessening inequality more than the problem it is meant to solve?

The Western philosophical tradition, though often invoked by those who counsel against bold policy, has rarely accepted this proposition. In fact, it offers some sharp answers to the question too often ignored in contemporary discussions: why should inequality worry us? Plato, for example, associated economic inequality with ineffective citizenship at either end of the spectrum. For him, the rich become lazy and inattentive to their responsibilities, and the poor lack the resources to succeed. For Thomas Hobbes, the extremely prosperous can employ their resources to undermine sovereign authority, while the impoverished become agitated and restless.

Yet perhaps the most important and influential philosopher of inequality was the eighteenth-century Genevan, Jean-Jacques Rousseau. Having grown up in poverty, he became one of the Enlightenment’s most feted intellectuals – becoming a full-blown celebrity in an age that amply rewarded his talents. Yet he consciously shunned the wealth that typically accompanied such achievements in his age (unlike his bitter rival Voltaire).

Rousseau witnessed inequality’s effects on his own beloved native city, which was transitioning from a feudal to capitalist economy centered on nascent manufacturing and, more notably, international banking. It was with this transformation in mind that Rousseau insisted in his “Discourse on Political Economy,” “one of the most important tasks of government [is] to prevent extreme inequality of fortunes.”

Rousseau describes several threats to the public good posed by economic inequality. First, the wealthy are in a position to shape the laws to serve their own interests, typically at the expense of the poor. This is the central narrative of his “Discourse on the Origins of Inequality.” For Rousseau, the wealthy tend to leverage their money into political power, all under the banners of freedom and equality. As he would observe in his “Social Contract,” “Under bad governments . . . equality is only apparent and illusory; it serves only to maintain the poor in his misery and the rich in his usurpation.” More economically equal societies, by contrast, result in fairer laws – serving what he called the “general will” of the entire community, rather than the “particular will” of the financially privileged. It is this fear that fuels concern about Citizens United, for example, where an appeal to “freedom” might be used to advance the particular interests of some at the expense of the rest.

A second concern for Rousseau is the threat economic inequality poses to civic concord. As he laments in “Discourse on the Origins of Inequality,” “From the extreme inequality of Conditions and fortunes . . . one would see Chiefs foment everything that can weaken assembled men by disuniting them; . . . everything that can inspire mistrust and mutual hatred in the different estates by setting their Rights and interests at odds, and so strengthen the Power that contains them all.” In this way, the exceedingly wealthy use their power to turn the poor against one another, so as to distract them from those who exercise real societal power. As Wisconsin Gov. Scott Walker candidly confessed to a billionaire donor, one goal of targeting public-employee unions in his state was to “divide and conquer” the working classes – by pitting private workers against public employees and non-union workers against union members – in order to consolidate political gains.

But perhaps the most pernicious effects of economic inequality, for Rousseau, are wrought on the soul. Tremendous wealth, on his reasoning, enfeebles the conscience. We social animals are always driven to distinguish ourselves, to prove ourselves better than others. This is not always socially destructive, insofar as distinction is granted for the right reasons – namely, civic and sociable behavior. Society, however, has increasingly not only rewarded distinction with wealth, but made wealth a distinction worthy of respect. Where this happens, one’s status owes not just to one’s wealth per se, but to one’s wealth relative to the poverty of others. Rousseau worried that in the most unequal societies, the rich would acquire a “pleasure of dominating” that renders them “like those ravenous wolves which once they have tasted human flesh scorn all other food, and from then on want only to devour men.” Against a mind degraded in this way, addicted to the pleasure of domination, no appeal to justice, fairness, or any other value we like to think defines us, can have any effect; and no just society can stand on such foundations.

If the current discussion of economic inequality is to matter, it must transcend mere platitudes and identify the potential problems generated by wealth disparities. And Rousseau offers at least one avenue to engaging that substantive debate. It is possible that his arguments are misguided. But they are capable of empirical testing – and there is some recent evidence that his arguments might well prove true. In any case, Rousseau counsels not merely to acknowledge inequality, but to confront the full dimensions of its effects.