In the Iliad, Hector openly tells his wife that he is doomed to fall in the battle, because he shares with the audience a knowledge of the over-arching story in which he finds himself. This shared knowledge is poignant, heartbreaking, solemn, but not ironic; there is no tension between what Hector knows of the eventual outcome and what we know. In Plato, history is what makes the difference between our full knowledge of the outcome and the characters’ limited knowledge of it: the dialogues are generally set in the past, so that we see and hear Socrates and Agathon and Alcibiades and other long dead persons, happily carousing in the explicit hope that their lives might turn out well, justice might be served, Athens might appreciate them, when Plato knew those hopes had already been disappointed in the meantime.
Irony like that is partly an inheritance of the tragic drama (where the ignorant Oedipus curses “the criminal” to an audience that knows what he doesn’t know, namely that Oedipus is the guilty one). But what makes for the special emotional flavor of this Platonic irony is the way that history, rather than myth, supplies the outcome, known to writer and audience but unknown to the characters. Historians like Herodotus and Thucydides had already used this kind of historical irony for their own historiographical purposes. But in Plato, the real Athens and the fates of its inhabitants are the mere furniture of philosophical discussions which transcend the particulars of Socrates’ death, Alcibiades’ rise and fall — even Athens’ loss of the Peloponnesian war is, in the bright light of philosophy, just another instance of all-too-human folly chasing the wrong object of desire. That’s why the dialogues can be read without the accompanying historical background: the background helps, since Plato’s irony deliberately exploits it for dramatic effect, but it isn’t strictly necessary, because that same irony reduces the historical material to an overtone supporting the dominant note. That dominant note is, nearly always, philosophical.
Part of the sweet pain of reading this author closely is receiving just this set of mixed signals: one the one hand, Plato seems committed to the local and particular details of these characters, this setting, these gestures and faces — after all, he evokes them in such memorable ways, and they so frequently encode significant addenda to his arguments. On the other hand, his whole project is directed toward freeing us from our attachment to lovable particulars, thereby protecting us from their claim on our attention and from the possibility of their painful loss. Everyone in the Socratic circle, including Plato, lost his mentor in 399, and as we hear from Alcibiades at 221c, “one searches and finds nobody even close [i.e., similar] to him.” For Plato, that experience may have been central in driving home the awful precariousness of human happiness as we know it, and inciting him to the kind of voyage-of-ascent he urges upon us in Diotima’s discourse at 205-212. (From Chapter One, “Historical Context”).