Moral Freedom: The Search for Virtue in a World of Choice, by Alan Wolfe. W.W. Norton 224 pages, $24.95.

As every parent knows, sometimes the only answer to "Why?" is "Because I say so." For a long time that was, at least in form, the most common answer to society's ultimate why question: "Why be moral?" And of course, for an even longer time that question rarely arose, which greatly simplified matters.