Plato frequently shows Socrates inventing myths. Whatever one may think about why this is (shelves have been written about it), I regard the interface between philosophy and myth as of paramount significance; it is neither an accident of genealogy or an idiosyncrasy of certain writers.
A myth is a kind of fiction, but unlike ordinary fiction its denizens seem to have not less but more reality than the inhabitants of our ordinary and familiar world. There is a curious parallel between mythification and what Viktor Shklovsky called ostranenie or "defamiliarization," a notion I have had recourse to before. The latter effect renders us "estranged" from the familiar, usually by some striking trope or vivid description, inflecting the ordinary in such a way as to show it shot through either with significance or with an uncanny refusal of significance. Mythification can also effect this, not however by contrasting the ordinary with some conventional setting (making it stand out against it), but rather precisely by placing it into such a conventional system. "The wine-dark sea," "flashing-helmeted Hector", and so on, are only the smallest-scale examples of the workings of such a system, which extended as far as vast interpretive parallels between various events, natural phenomena, and concepts. These equivalences are indeed conventional, i.e., "arbitrary," and philosophy must address itself to understanding them as such, because treating them as "natural" is just superstitious. But philosophy's myths are meant to indicate their own fictitious status in a way that does not undermine the effect of estrangement, but rather produces it in a particularly philosophical mode. A conscious mode, I want to say, though that's only partly accurate.
The long-time reader of SCT will note that this notion has some resonance with earlier posts on fiction, theme, and secondary worlds. Or, to refer back to just yesterday, the whole notion of defamiliarization is a close parallel to the seeing of an object as "withdrawn"--the perplexing or even uncanny vorhanden hammer instead of the friendly, accessible zuhanden one, or (to switch from Heidegger to Sartre) the eerie, nausea-inducing tree-root that refuses any appellation rather than the one to which the word "root" obligingly adheres.
(Part of these reflections was sparked by reading chapter 4 of Thomas Pavel's Fictional Worlds.)