There is much to be said for this picture, give or take the naked Germans. The Enlightenment was a broad phenomenon—often, we use it as a synonym for "modern life"—but its outcomes depended on local variations. This is the relationship of climate and weather: the varieties of the latter confirm the stability of the former, but the relationship between the two is always unstable. Vincenzo Ferrone, the Italian author of the forthcoming Enlightenment: History of an Idea, calls the Enlightenment a "centaur": an impossible combination. It was a set of abstract philosophical ideals, but it was also a lived historical experience, full of ordinary disappointments and irregularities. We know what a centaur should look like, but we never see one in real life.

"Ah, but a man's reach should exceed his grasp," Browning wrote, "Or what's a heaven for?" The Enlightenment was the first modern "theory of everything." Out with empires, slaves, and priests; in with nations, free minds, and free publics. If the world could be known entirely, society could be reconstructed along improved lines. That, at least, was the theory. In practice, some of the Enlightenment's local variations were terrifying, not least because the theorists of the Enlightenment thought they knew better than everyone else. The Enlightenment was made by intellectuals, and frequently for them, too. The modern intellectual prides himself on his selfless rectitude but, like the medieval churchman whose power he supplanted, he can spy a distant horizon because he looks down from a lofty height. Voltaire reviled the church, but thought religion was a good way to keep the plebs in line: better that the little folks clung to their religion than to their guns. Rousseau loathed authority, but he awarded his Enlightened state the dictator's privilege of "forcing people to be free."

"These days," Goethe said, "there remains no doubt that world history has from time to time to be rewritten." Historically, managerial elitism has been a reliable paver of the road to hell. Today, the technocrats chase a mirage of perfection, allegedly on our behalf. Lawrence Lessig tells us that we should abandon the eighteenth-century ideals of intellectual copyright, and the Constitution; perhaps Google can sponsor a Second Constitutional Convention? Cass Sunstein tells us that we cannot be trusted to make informed decisions, so the government must "nudge" us toward "healthy" choices. Why let us eat cake, when we can be forced to make free at the salad bar? These are odious ideas, the kind of suggestions that Rousseau might have made if he had worked in advertising. They reflect a widening distance between the governors and the governed, the tenured and the temporary, the rich and the poor.

The greatness of the Enlightenment lies less in its ideals, than in our efforts to realize them. The tragedy of the Enlightenment lies there too. History is made in the middle ground between theory and practice. But the middle ground, economic, social, and political, is a bad place to be in the modern West. The Enlightenment was never automatically democratic in the modern sense. The path from the Enlightenment ideal of Nature to the Enlightenment politics of natural rights often ran into the mud of the middle ground. Intellectually, the Enlightenment was always an elite business. And in business, ethics are always challenged by commercial realities.