From, A History of Greek Philosophy, vol. IV, Plato: the man and his dialogues, earlier period,
Cambridge University Press, 19896, pp. 8-38.
To lead up to these latter journeys, which were of greater importance in his life, something must be said about the development of his attitude to politics and philosophy, as he himself (or, if this is preferred, an intimate friend who knew his thoughts) has described it in the Seventh Letter. As a young man, like most Athenians of his class, he supposed he would go straight into politics, but his early twenties coincided with the defeat οf Athens and the oligarchic revolution leading to the government of the Thirty. ‘Some of these’, continues the Letter, ‘were relatives and acquaintances of mine, and at once urged it on me as a suitable course to join their activities.’ Being young and idealistic, Plato assumed that their aim would be to raise the moral standards of government, and he watched to see what they would do. Young as he was, the main lines of his character are beginning to show. Whereas most twenty-three-year-olds would have jumped without hesitation at the opportunity offered them by a Critias or a Charmides, he watched and waited; and what he saw of their excesses so shocked him that he simply ‘withdrew himself from the evils of the time’.
A Day in Old Athens * A Short History of Greek Philosophy
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Reference address : https://www.ellopos.net/elpenor/greek-texts/ancient-Greece/guthrie-plato.asp?pg=8