“Secularism” is a late coinage in English, dating from the 1850s, when it was adopted by reformers who regarded the church and capital as the joint enemies of the worker (Holyoake 1854). But because the word is used by cultural critics in many antithetical senses, it occasions great confusion. The United States is sometimes held to be the model of secular democracy and sometimes the most religious of all major modern democracies. Can both be true? The root “secular” derives from the Latin for “the age”; in the Christian tradition, the secular is the temporal or the worldly. The spiritual/secular opposition is fundamental, but Christian attitudes toward the secular have ranged from hostility to fervent immersion and have seldom been simple. It was at one time possible, for example, to speak of “secular clergy,” by which was meant ordinary parish priests, as opposed to the religious of the monastic orders. Protestantism heightened the contrast, and Puritans especially differentiated spiritual and secular functions as part of their critique of the established church. Thus they relegated marriage to secular authorities and avoided the ecclesiastical courts. But they did not imagine the secular to be outside of Christianity, let alone outside of the...