Now if my present task were to write about the Cynic philosophy, I could add many details about the Cynics, not less important than what I have said already. But not to interrupt my main theme, I will now consider in due course the question what kind of myths ought to be invented. But perhaps another inquiry should precede this attempt, I mean to what branch of philosophy the composition of myths is appropriate. For we see that many philosophers and theologians too have employed it, Orpheus for instance, the most ancient of all the inspired philosophers, and many besides of those that came after him. Nay what is more, Xenophon as we know and Antisthenes and Plato often introduced myths, so that it is obvious that even if the use of myth be not appropriate for the Cynic, still it may be so for some other type of philosopher.
I must first then say a few words about the subdivisions or instruments of philosophy. It does not make much difference in which of two ways one reckons logic, whether with practical or natural philosophy, since it is equally necessary to both these branches. But I will consider these as three separate branches and assign to each one three subdivisions. Natural philosophy consists of theology, mathematics, and thirdly the study of this world of generation and decay and things that though imperishable are nevertheless matter, and deals with their essential nature and their substance in each case. Practical philosophy again consists of ethics in so far as it deals with the individual man, economics when it deals with the household as a unit, politics when it deals with the state. Logic, again, is demonstrative in so far as it deals with the truth of principles; polemic when it deals with general opinions;  eristic when it deals with opinions that only seem probabilities. These then are the divisions of philosophy, if I mistake not. Though indeed it would not be surprising that a mere soldier should be none too exact in these matters or not have them at his fingers' ends, seeing that I speak less from book-knowledge than from observation and experience. For that matter you can yourselves bear me witness thereto, if you count up how few days have elapsed between the lecture that we lately heard and today, and moreover the number of affairs with which they have been filled for me. But as I said if I have omitted anything - though I do not think I have - still if anyone can make my classification more complete he will be “no enemy but my friend.”
Now of these branches of philosophy, logic has no concern with the composition of myths; nor has mathematics, the subdivision of natural philosophy; but they may be employed, if at all, by that department of practical philosophy which deals with the individual man, and by that department of theology which has to do with initiation and the Mysteries. For nature loves to hide her secrets, and she does not suffer the hidden truth about the essential nature of the gods to be flung in naked words to the ears of the profane. Now there are certain characteristics of ours that derive benefit from that occult and unknown nature, which nourishes not our souls alone but our bodies also, and brings us into the presence of the gods, and this I think often comes about by means of myths; when through riddles and the dramatic setting of myths that knowledge is insinuated into the ears of the multitude who cannot receive divine truths in their purest form.
It is now evident what branch and what sort of philosophy may properly on occasion employ myths. And to support my argument I call to witness the authority of those philosophers who were the first to use myths. Plato for instance in his theological descriptions of life in Hades often uses myths, and the son of Calliope before him.  And when Antisthenes and Xenophon and Plato himself discuss certain ethical theories they use myths as one of the ingredients, and not casually but of set purpose. Now if you too wished to use myths you ought to have imitated these philosophers, and instead of Heracles you should have introduced the name of Perseus or Theseus, let us say, and have written in the style of Antisthenes; and in place of the dramatic setting used by Prodicus, in treating of those two gods you should have introduced into your theatre another setting of the same sort.
Source: The Works of the Emperor Julian, volume II (1913) Loeb Classical Library. Translated by Emily Wilmer Cave Wright.