In ‘Plato’s defence of Forms in the Parmenides’ (on my website) I’ve argued that Plato wrote the Parmenides after his return from Syracuse in 366 B.C., and that he wrote it for his disciples in the Academy to fortify them against any possible attacks against the theory of the Forms after his planned return to Syracuse. He did so by exposing the theory of Forms of a very young Socrates, with which the latter challenged Parmenides’ ‘All is one’ thesis, to Parmenides’ criticism. The discussion was diligently rehearsed by Plato’s half-brother Antiphon; in the dialogue Plato’s brother Adeimantus (and implicitly his brother Glaucon, who accompanies Adeimantus) vouches for it. This means that Plato himself, like his brothers was well aware of all those arguments against the Forms; these arguments had no relevance to Forms that he himself discovered. And so he can let his Parmenides step out of his historical persona, predict the coming of an exceptional man who will discover Forms immune against all ‘refutations’ (Parm. 133b4-135b2).
Plato returned to Athens in 366 B.C. with the intention to return to Syracuse in a year. When his stay in Athens became protracted, Plato had to think of finding ways how to fortify Dionysius against the attacks against his theory of Forms by sophists with which Dionysius surrounded himself. The Parmenides became suddenly primarily important in Plato’s relation to Dionysius. But there was a problem. The Parmenides as it was originally written for Plato’s disciples in the Academy pointed to the Republic as its necessary companion. This connection became problematic, for the main tenet animating the Republic, the postulated unity between philosophy and political power, became the main target of Plato’s detractors in Syracuse, and thus of Dionysius’ suspicions: ‘What does Plato really want?’ Moreover, Plato needed to present Dionysius with a dialogue that nothing the sophists around him could offer him might match. And so he wrote the Symposium in which he conjures up an ideal philosopher in the guise of a priestess Diotima, whom nobody can accuse of hankering after political power. As Plato’s stay in Athens became even more protracted, this point had to be made more strongly and more explicitly. And so Plato wrote the Sophist in which the Eleatic Stranger maintains that Sophist, Statesman, and Philosopher are different from each other.
In the Parmenides itself Plato did his best to show that Parmenides’ arguments against the Forms only looked like saying something important, but in fact were a pack of falsities; he emphasized this by the fact that Parmenides’ arguments against the Forms diligently memorised by Antiphon did not turn the latter to philosophy; Adeimantus in the preamble to the dialogue mentions that when Antiphon grew up he devoted himself to horsemanship (Parm. 126c). This point is emphasised in the Symposium; in its preamble we meet with Glaucon who was interested in doing anything else but philosophy. Obviously, Parmenides’ arguments against the Forms he heard Antiphon memorizing turned him away from philosophy; it was Socrates’ speech on love presented at Agathon’s banquet, which Apollodorus narrated to him, that made him a worthy partner in discussion with Socrates in the Republic.
As Plato secured the connection between the Parmenides and the Republic in the preamble to the Parmenides, and the connection between the Symposium, Parmenides, and the Republic in the preamble to the Symposium, so he secured the all-important connection of the Sophist to the Parmenides in the preamble to the Sophist. Theodorus opens the dialogue by introducing the Eleatic Stranger to Socrates as ‘a disciple of Parmenides and Zeno’ (hetairon tȏn amphi Parmenidȇn te kai Zȇnȏna, 216a3-4), and Socrates asks the Stranger whether he prefers to define the Sophist, Statesman, and Philosopher my making a long oration, or by the method of questions (di’ erȏtȇseȏn), ‘which Parmenides employed when he was going through very beautiful arguments (diexionti logous pankalous) in a discussion at which I was present as a young man; he was at that time already very old’ (217c).
The whole point of the Parmenides is to show that arguments Parmenides had raised against the Forms were falsities (Parm. 133b7) and only appeared to be ‘saying something’ (dokein ti legein, 135a6), while in fact they were empty talk. It appears that in the Sophist Plato strongly re-emphasizes this point. For in the Parmenides, Parmenides ends his criticism of the theory of Forms of the young Socrates by pointing to him that he began to define the Forms too early: ‘Train yourself more thoroughly while you are still young; drag yourself more through what is generally regarded as useless, and condemned by the multitude as idle talk (adoleschia).’ (Parm. 135d, tr. R. E. Allen) Adoleschia ‘idle talk’ comes to the fore in the Sophist within the framework of the Stranger’s definition of the Sophist as an Eristic that differs from the adoleschikos, the man of ‘idle talk’, only in so far as he earns his money by getting engaged in disputations, whereas the adoleschikos neglects his own affairs and gets impoverished because of his delight in disputations (Soph. 225c-d). In the Sophist the Eristic is characterised as antilogikos (225b10), a man pitting argument against argument. When Socrates asks Parmenides what does this training, viewed as adoleschia, consist of, the latter explains: ‘It is necessary to examine the consequences that follow from the hypothesis, not only if each thing is hypothesized to be, but also if that same thing is hypothesized not to be.’ (135e9-136a2, tr. Allen).