Karl Marx's writings contain, besides economic analysis and the political theory of revolutionary communism, an influential sociology of ideas, explaining how social life shapes and distorts people's ideas and beliefs. This book presents a fresh critical study of this theory, establishing what Marx did and did not say, and distinguishing the more scientific parts of his thought from those that were overly influenced by his revolutionary aims. The author argues that Marx's own theory of ideas can play an important role in explaining the subsequent degeneration of Marxist thought itself.