groups who are interested in the occurrence of this phenomenon (sometimes it is a hidden interest which has first to be revealed), and who have planned and conspired to bring it about." He argues that the main task of social sciences is to analyze the unintended social repercussions of intentional human actions. He concludes that psychological analysis should not be used to develop a standard of what is considered rational behavior in a particular situation, and that the problems of society are irreducible to those of human nature. Chapter 15, "Economic Historicism", discusses Marx's "historical materialism" philosophy, which replaces Hegelian psychologism with materialism. Popper argues that Marx did not believe economic motives caused social and historical changes, but rather saw them as symptoms of corrupt social systems. Marx viewed social science as scientific history focused on the material conditions of society, but Popper criticizes his historicism while supporting his economism, "i.e. the claim that the economic organization of society, the organization of our exchange of matter with nature, is fundamental for all social institutions and especially for their historical development." Popper believes that Marx's economism is valuable because it emphasizes the fundamental role of economic organization in all social institutions and historical development, but warns against reductionist and essentialist views. Chapter 16, "The Classes", discusses Marx's statement that "the history of all hitherto existing society is a history of class struggles", and its implications that history is determined by the war of classes rather than nations. He explains Marx's theory of classes as an institutional or objective social situation that influences human minds and makes them act accordingly. Popper notes the dangers of oversimplifying political conflicts as struggles between exploiters and exploited, and warns of the dangers inherent in Marx's sweeping historicist generalization. Despite his criticisms, Popper finds admirable Marx's attempt to use the "logic of the class situation" to explain the working of institutions in the industrial system. Chapter 17, "The Legal and the Social System", discusses Marx's theory of the state and the implications for political action. Marx believed that the legal and political system was a superstructure upon the actual productive forces of the economic system, and the state was an organ for class domination. Popper argues that although Marx's theory was insightful, it contained only a grain of truth and has been refuted by subsequent experience. Popper suggests that economic interventionism is necessary to safeguard freedom,