
The fundamental argument of Plato’s critique of rhetoric usually is exemplified by the thesis, maintained, among other things, in the Gorgias, that only he who "knows" [epistatai] can speak correctly; for what would be the use of the "beautiful," of the rhetorical speech, if it merely sprang from opinions [doxa], hence from not knowing? … Plato’s … rejection of rhetoric, when understood in this manner, assumes that Plato rejects every emotive element in the realm of knowledge. But in several of his dialogues Plato connects the philosophical process, for example, with eros, which would lead to the conclusion that he attributes a decisive role to the emotive, seen even in philosophy as the absolute science.
Source: Rhetoric as Philosophy (1980), p. 28