In the Protagoras (324d) a distinction is made between muthos and logos, where muthos appears to refer to a story and logos to an argument. This distinction seems to be echoed in theTheaetetus and the Sophist. In the Theaetetus Socrates discusses Protagoras’ main doctrine and refers to it as “the muthos of Protagoras” (164d9) (in the same line Socrates also calls Theaetetus’ defence of the identity of knowledge and perception a muthos). And later on, at 156c4, Socrates calls a muthos the teaching according to which active and passive motions generate perception and perceived objects. In the Sophist, the Visitor from Elea tells his interlocutors that Xenophanes, Parmenides and other Eleatic, Ionian (Heraclitus included) and Sicilian philosophers “appear to me to tell us a myth, as if we were children” (242c8; see also c–e). By calling all those philosophical doctrines muthoi Plato does not claim that they are myths proper, but that they are, or appear to be, non-argumentative. In the Republic Plato is fairly hostile to particular traditional myths. And in many dialogues he condemns the use of images in knowing things and claims that true philosophical knowledge should avoid images. He would have had strong reasons for avoiding the use of myths: they are not argumentative and they are extremely visual (especially those he invented, which contain so many visual details as if he would have given instructions to an illustrator). But he didn’t.
He wanted to persuade and/or teach a wider audience, so he had to make a compromise. Sometimes, however, he seems to interweave philosophy with myth to a degree that was not required by persuading and/or teaching a non-philosophical audience. The eschatological myths of the Gorgias, Phaedo and Republic, for instance, are tightly bound with the philosophical arguments of those dialogues (cf. Annas 1982); and the eschatological myth of the Phaedo “picks one by one the programmatic remarks about teleological science from earlier on in the dialogue, and sketches ways in which their proposals can be fulfilled” (Sedley 1990, 381). Some other times he uses myth as a supplement to philosophical discourse (cf. Kahn (2009) who argues that in the myth of the Statesman Plato makes a doctrinal contribution to his political philosophy). And one time, in the Timaeus, he appears to overcome the opposition between muthos and logos: human reason has limits, and when it reaches them it has to rely on myth.
“On the less radical version, the idea will be that the telling of stories is a necessary adjunct to, or extension of, philosophical argument, one which recognizes our human limitations, and—perhaps—the fact that our natures combine irrational elements with the rational” (Rowe 1999, 265). On a more radical interpretation, “the distinction between ‘the philosophical’ and ‘the mythical’ will—at one level—virtually disappear” (265). If we take into account that Plato chose to express his thoughts through a narrative form, namely that of the dialogue (further enveloped in fictional mises en scène), we may say that the “use of a fictional narrative form (the dialogue) will mean that any conclusions reached, by whatever method (including ‘rational argument’), may themselves be treated as having the status of a kind of ‘myth’” (265). If so, “a sense of the ‘fictionality’ of human utterance, as provisional, inadequate, and at best approximating to the truth, will infect Platonic writing at its deepest level, below other and more ordinary applications of the distinction between mythical and nonmythical forms of discourse” (265); if so, it is not only “that ‘myth’ will fill in the gaps that reason leaves (though it might do that too, as well as serving special purposes for particular audiences), but that human reason itself ineradicably displays some of the features we characteristically associate with story-telling” (265–6). It is difficult to say which one of these two readings is a better approximation of what Plato thought about the interplay between myth and philosophy. The interpreter seems bound to furnish only probable accounts about this matter.