To desire one's own economic advancement is comparatively reasonable; to Marx, who inherited eighteenth-century rationalist psychology from the British orthodox economists, self-enrichment seemed the natural aim of a man's political actions. But modern psychology has dived much deeper into the ocean of insanity upon which the little barque of human reason insecurely floats. The intellectual optimism of a bygone age is no longer possible to the modern student of human nature. Yet it lingers in Marxism, making Marxians rigid and Procrustean in their treatment of the life of instinct. Of this rigidity the materialistic conception of history is a prominent instance