Much of the intense current interest in collective memory concerns the politics of memory. In a book that asks, "Is there an ethics of memory?" Avishai Margalit addresses a separate, perhaps more pressing, set of concerns. The idea he pursues is that the past, connecting people to each other, makes possible the kinds of "thick" relations we can call truly ethical. Thick relations, he argues, are those that we have with family and friends, lovers and...