Rousseau’s lowly background made him the Enlightenment’s great outsider. Illustration by Jeffrey Fisher

“I love the poorly educated,” Donald Trump said during a victory speech in February, and he has repeatedly taken aim at America’s élites and their “false song of globalism.” Voters in Britain, heeding Brexit campaigners’ calls to “take back control” of a country ostensibly threatened by uncontrolled immigration, “unelected élites,” and “experts,” have reversed fifty years of European integration. Other countries across Western Europe, as well as Israel, Russia, Poland, and Hungary, seethe with demagogic assertions of ethnic, religious, and national identity. In India, Hindu supremacists have adopted the conservative epithet “libtard” to channel righteous fury against liberal and secular élites. The great eighteenth-century venture of a universal civilization harmonized by rational self-interest, commerce, luxury, arts, and science—the Enlightenment forged by Voltaire, Montesquieu, Adam Smith, and others—seems to have reached a turbulent anticlimax in a worldwide revolt against cosmopolitan modernity.

No Enlightenment thinker observing our current predicament from the afterlife would be able to say “I told you so” as confidently as Jean-Jacques Rousseau, an awkward and prickly autodidact from Geneva, who was memorably described by Isaiah Berlin as the “greatest militant lowbrow in history.” In his major writings, beginning in the seventeen-fifties, Rousseau thrived on his loathing of metropolitan vanity, his distrust of technocrats and of international trade, and his advocacy of traditional mores.

Voltaire, with whom Rousseau shared a long and violent animosity, caricatured him as a “tramp who would like to see the rich robbed by the poor, the better to establish the fraternal unity of man.” During the Cold War, critics such as Berlin and Jacob Talmon presented Rousseau as a prophet of totalitarianism. Now, as large middle classes in the West stagnate and billions elsewhere move out of poverty while harboring unrealizable dreams of prosperity, Rousseau’s obsession with the psychic consequences of inequality seems even more prophetic and disturbing.

Rousseau described the quintessential inner experience of modernity: being an outsider. When he arrived in Paris, in the seventeen-forties, at the age of thirty, he was a deracinated looker-on, struggling with complex feelings of envy, fascination, revulsion, and rejection provoked by a self-absorbed élite. Mocked by his peers in France, he found keen readers across Europe. Young German provincials such as the philosophers Johann Gottlieb Fichte and Johann Gottfried von Herder—the fathers, respectively, of economic and cultural nationalism—simmered with resentment toward cosmopolitan universalists. Many small-town revolutionaries, beginning with Robespierre, have been inspired by Rousseau’s hope—outlined in his book “The Social Contract” (1762)—that a new political structure could cure the ills of an unequal and commercial society.

In the past decade, a number of books have asserted Rousseau’s centrality and uniqueness. Leo Damrosch’s biography, “Restless Genius” (2005), identified Rousseau as “the most original genius of his age—so original that most people at the time could not begin to appreciate how powerful his thinking was.” Last year, István Hont, in “Politics in Commercial Society,” a comparative study of Rousseau and Adam Smith, argued that we have not moved much beyond Rousseau’s fears and concerns: that a society built around self-interested individuals will necessarily lack a common morality. Heinrich Meier, in his new book, “On the Happiness of the Philosophic Life” (Chicago), offers an overview of Rousseau’s thought through a reading of his last, unfinished book, “Reveries of a Solitary Walker,” which he began in 1776, two years before his death. In “Reveries,” Rousseau moved away from political prescriptions and cultivated his belief that “liberty is not inherent in any form of government, it is in the heart of the free man.”

If Rousseau seems like the central protagonist in the anti-élitist revolt currently reconfiguring our politics, it is because he was present during the creation of the value system—the Enlightenment belief in what he called “the sciences, the arts, luxury, commerce, laws,” which changed the character of Western culture and eventually that of the world at large. The new dispensation generally benefitted men of letters. Rousseau, however, became one of its rare critics, at least partly because the Paris salon, the focal point of the French Enlightenment, was a milieu in which he had no real place.

Rousseau had little formal education, but he accumulated plenty of experience during a largely unsupervised childhood and adolescence. Born in Geneva in 1712, to a struggling watchmaker and a mother who died shortly after giving birth, he was only ten years old when his father deposited him with indifferent relatives and left town. At the age of fifteen, he ran away and found his way to Savoy, where he quickly became the boy toy of a Swiss-French noblewoman. She turned out to be the great love of his life, introducing him to books and music. Rousseau, always seeking substitutes for his mother, called her Maman.

By the time he arrived in Paris, he had already worked in various subordinate capacities throughout Europe: as an apprentice engraver in Geneva, a footman in Turin, a tutor in Lyons, a secretary in Venice. These experiences, Damrosch writes, “gave him the authority to analyze inequality as he did.” Soon after his move to Paris, he took up with a near-illiterate laundress, who bore him five children, and made his first tentative forays into salon society. One of his earliest acquaintances there was Denis Diderot, a fellow-provincial who was committed to making the most of that decade’s relatively free intellectual climate. In 1751, Diderot launched his “Encyclopédie,” which synthesized key insights of the French Enlightenment, such as those of Buffon’s “Natural History” (1749) and Montesquieu’s hugely influential “The Spirit of the Laws” (1748). The encyclopedia cemented the movement’s main claim: that knowledge of the human world, and the identification of its fundamental principles, would pave the path of progress. As a prolific contributor to the “Encyclopédie,” publishing nearly four hundred articles, many of them on politics and music, Rousseau appeared to have joined in a collective endeavor to establish the primacy of reason and, as Diderot wrote, to “give back to the arts and the sciences the liberty that is so precious to them.”

But his views were changing. One afternoon in October, 1749, Rousseau travelled to a fortress outside Paris, where Diderot, who had tested the limits of free expression with a tract that challenged the existence of God, was serving a few months in prison. Reading a newspaper on the way, Rousseau noticed an advertisement for an essay competition. The topic was “Has the progress of the sciences and arts done more to corrupt morals or improve them?” In his “Confessions,” published in 1782, and arguably the first modern autobiography, Rousseau described how “the moment I read this I beheld another universe and became another man.” He claims that he sat down by the roadside and spent the next hour in a trance, drenching his coat in tears, overcome by the insight that progress, contrary to what Enlightenment philosophes said about its civilizing and liberating effects, was leading to new forms of enslavement.

Rousseau is unlikely to have received his epiphany so histrionically; he may have already started formulating his heresies. In any case, his prize-winning entry in the contest, published in 1750 as his first philosophical work, “A Discourse on the Moral Effects of the Arts and Sciences,” abounded in dramatic claims. The arts and sciences, he wrote, were “garlands of flowers over the chains which weigh [men] down,” and “our minds have been corrupted in proportion” as human knowledge has increased. By the mid-eighteenth century, Paris’s intellectuals had erected a standard of civilization for others to follow. In Rousseau’s view, the newly emergent intellectual and technocratic class did little more than provide literary and moral cover for the powerful and the unjust.