From Plato onward, western moral and political philosophy has been dominated by a monist impulse manifest in a search for the best way of life, the best form of government, the perfect society, the highest human faculty, the highest or the best religion, the single most reliable way to acquire knowledge of the world, and so on. In ethics it has taken the form of moral monism or the view that one way of life can be rationally shown to be the highest or truly human. This view has commanded the allegiance of Plato, Aristotle, Augustine, Aquinas, Locke, Mill, Marx, and others. Because monism despises neglected human faculties, virtues, and ways of life and has been a source of much violence and oppression, we cannot hope to provide a coherent theory of human liberation and freedom without developing a coherent theory of moral and cultural pluralism. Although moral monism was challenged from the very beginning by the Sophists, the skeptics, and others, a systematic critique of it was not mounted until the eighteenth century by such writers as Vico, Montesquieu, Montaigne, Herder, and others, who stressed the inevitability and even the desirability of cultural diversity.