open societies and closed societies These terms were introduced by Karl Popper in his book The Open Society and its Enemies (1945), and further explored in The Poverty of Historicism (1957). Popper argued that both science and human history are essentially indeterminate and fluid. Applied to social theory, this produced Popper's lively and devastating attack on historicism. Theories such as those of Plato, Hegel, and Marx, which proposed the existence of laws of history and a knowable human destiny, were dismissed by Popper as scientifically insupportable and politically dangerous. He proposed that all such theories would lead to authoritarian and inhumane regimes, which he called closed societies because they were closed to the normal processes of change. Open societies by contrast were based on the activity, creativity, and innovation of many individuals, and would develop unpredictably through piecemeal social engineering. They are those societies in which social policies are monitored for unintended consequences, openly criticized, and altered in the light of such criticism. Such societies must be both liberal and democratic, in the sense that it must be possible to remove from office rulers who fail to respond to justified criticism. The implied contrast, of course, was between the totalitarian regime of what was then the Soviet Union (as a closed society) and the Western democracies (as open societies).

Popper's arguments were rightly seen as decisive logical refutation of the very foundations of Marxism—both its claim to scientific status, and its claim to reveal the course of future history.