Popper finalizes his discussion of Plato by examining the historical development from a closed to an open society with broad strokes. Of particular interest is one turning point in the history of Western civilization, for which ancient Greece was the source (163). This turning point was the Peloponnesian War between the city-states of Sparta and Athens—and much of the Greek world as a result of alliances.

The Great Generation of Athens is the reason why Popper considers this time period significant. This group included several intellectuals who were the early proponents of what eventually developed into an open society. One such example was Pericles, the “great leader of democracy […] who formulated the principle of equality before the law and of political individualism” (175). Popper also highlights the school of Gorgias, which included Alcidamas, Lychophron, and Antisthenes. He credits them with the establishment of central ideas to challenge slavery as an institution as well as anti-nationalism. Popper calls their work “the creed of the universal empire of men” (175). It is Socrates who is the greatest thinker of the Great Generation because he was a proponent of human reason, self-criticism, and intellectual honesty.