Morality is closely associated with religion in the minds of many people. When religious leaders speak out on moral topics, their opinions are often treated with special deference. They are regarded as moral experts. This raises the question of whether morality depends in some way on religion. Many philosophers have held that it does. John Locke, for example, argued that atheists could not be trusted to be moral because they would not consider themselves obliged even by solemn oaths, much less by ordinary promises. The answer to this question may be of considerable practical importance. If morality does depend on religion, the process of secularization, in the course of which religious belief and practice wither away, seems to pose a serious threat to morality. At one time many social theorists were confident that secularization was inevitable in modern and postmodern societies. Experience has undermined...