Love, persuasion, and the soul › Persuasion needs a subject to be true about

After the speeches, the conversation turns to what makes speaking and writing good. Socrates rejects the idea that authorship is shameful in itself; the relevant distinction is writing well or badly (258d). He asks whether a speaker must know the truth about the subject. Phaedrus reports the rival view that an orator needs what the audience believes, especially about justice and goodness, rather than what is actually true (259e–260a).

Socrates exposes the risk through a deliberately absurd example. A speaker who shares his audience's ignorance might praise a donkey as a horse and persuade them to acquire the wrong animal for war (260b–d). The larger point concerns mistaken judgments of good and bad. Agreement between speaker and audience does not make their judgment sound. Persuasion can succeed while making its hearers worse off.

The stronger argument concerns deception by resemblance. A skilled deceiver leads an audience from one thing to another through small similarities; doing this reliably requires distinguishing where things resemble one another and where they differ (261e–262c). Socrates therefore argues that an art of speech needs knowledge of reality. But this establishes an uncomfortable result: knowledge can improve someone's capacity to deceive. The claim that truth is necessary for genuine rhetorical expertise does not establish that an expert will speak honestly.

Nor does knowing the truth automatically provide the ability to persuade. The dialogue allows this distinction when rhetoric defends its contribution at 260d–e. Someone may understand a question and still be unable to explain it to a particular listener. The inquiry must therefore address both the structure of the subject and the condition of the person hearing about it. This is where dialectic and the knowledge of souls enter.