There are two critically important American ideas: first, that men and women of different religions, ethnicities, and races can live together in a single commonwealth; and second, that they can govern themselves democratically, arguing and deciding as free and equal citizens.

The combination of the two is perhaps what’s special to America—for it was once widely believed that self-government required a homogeneous group of citizens. By contrast, most Americans believed, almost from the beginning, that pluralism and democracy were compatible, even mutually enhancing. At first, to be sure, it was only religious pluralism that was valued; ethnicity and race came later (and not easily), but religion is the crucial issue today. The greatest threat to pluralism and democracy in the contemporary world is the belief that virtuous government requires religious homogeneity and clerical dominance: a single faith and a single version of God’s law.

Religious fundamentalists hold that believers, heretics, and infidels cannot govern themselves as equals, and that state policy cannot be the result of an open competition and a freewheeling debate in which everyone participates. Fundamentalists here at home are relative moderates on these questions; most important, they do not claim that it is right to terrorize and kill nonbelievers who don’t accept the rule of the faithful. But that’s precisely the claim made today by (some) Islamic radicals—and by radical members of other faiths too—and a lot of killing has followed from it. We resist with a “war on terror,” and that is sometimes—but only sometimes—a necessary war.

The larger struggle, however, has to do with ideas—American ideas, though they are no longer only ours. So we have to remember our original enthusiasm for both pluralism and democracy, and mount a passionate intellectual defense of the two together. And if we are to defend them persuasively, we had better make sure that these American ideas are more fully realized here in America than they currently are.