Beginning with a criticism of Plato (c. 428–c. 348 B.C.E.) and Karl Marx (1818–1883), Popper argued that Plato’s philosopher-kings represented an unattainable ideal of human wisdom and that Marx was mistaken in believing that human history has a moral dimension. Popper reasoned that rulers are always fallible human beings. Furthermore, Popper rejected “historicism,” or the view that history is determined by group actions, and “holism,” or the view that only groups are causal agents in society. He did not think that the social sciences had evidence for either the existence of impersonal forces in history or the view that anything other than individuals could make things happen.

Popper did not think it was possible for rulers to predict the consequences of their actions and policies. His grounds for this were the philosophical impossibility of anyone being able to predict the future. In an open society, policies should therefore be undertaken as hypotheses that are open to being proved false. Because rulers were capable of fooling themselves and others about the success of their policies, it should be left up to the people to evaluate whether a program was successful. And if it were assessed unsuccessful, then another program should be instigated, subject to the same corrections. Popper believed that if societies were not “open” in this way, then totalitarianism and repression of individual liberties would ensue.