[7] Popper saw the classical Greeks as initiating the slow transition from tribalism towards the open society, and as facing for the first time the strain imposed by the less personal group relations entailed thereby.
[9] Popper argued that the ideas of individuality, criticism, and humanitarianism cannot be suppressed once people have become aware of them, and therefore that it is impossible to return to the closed society,[10] but at the same time recognized the continuing emotional pull of what he called "the lost group spirit of tribalism", as manifested for example in the totalitarianisms of the 20th century.
In contrast, in an open society each citizen needs to engage in critical thinking, which requires freedom of thought and expression and the cultural and legal institutions that can facilitate this.
This was recognized by Pericles, a statesman of the Athenian democracy, in his laudatory funeral oration: "advancement in public life falls to reputation for capacity, class considerations not being allowed to interfere with merit; nor again does poverty bar the way, if a man is able to serve the state, he is not hindered by the obscurity of his condition.
"[20] Arguably however it was the tension between a traditional society and the new, more open space of the emerging polis which most fully marked classical Athens,[21] and Popper was very aware of the continuing emotional appeal of what he called "holism...longing for the lost unity of tribal life"[22] into the modern world.
"[24] Popper however, did not identify the open society either with democracy or with capitalism or a laissez-faire economy, but rather with a critical frame of mind on the part of the individual, in the face of communal group think of whatever kind.