Alasdair MacIntyre-whom Newsweek has called "one of the foremost moral philosophers in the English-speaking world"-here presents his 1988 Gifford Lectures as an expansion of his earlier work Whose Justice? Which Rationality? He begins by considering the cultural and philosophical distance dividing Lord Gifford's late nineteenth-century world from our own. The outlook of that earlier world, MacIntyre claims, was definitively articulated in the Ninth Edition of the Encyclopaedia Brittanica, which conceived of moral enquiry as both providing insight into and continuing the rational progress of mankind into ever greater enlightenment. MacIntyre compares that conception of moral enquiry to two rival conceptions also formulated in the late nineteenth century: that of Nietzsche's Zur Genealogie der Moral and that expressed in the encyclical letter of Pope Leo XIII Aeterni Patris.