Plutarch De E apud Delphos 15

[15] But, said I, the most important matter I fear may embarrass our Plato when it is stated, just as he said that Anaxagoras was embarrassed by the name of the Moon, since he tried to claim as his own some very ancient opinion in regard to its illumination. Has not Plato said this in the Cratylus? ¹

Certainly, said Eustrophus, but what similarity there is I do not see.

Well, you know, of course, that in the Sophist ² he demonstrates that the supreme first principles are five: Being, Identity, Divergence, and fourth and fifth besides these, Motion and Rest. ³ But in the Philebus ⁴ he employs another method of division and affirms that the Infinite is one and the Definite a second, and from the combination of these all generation arises. The cause which makes them combine he posits as a fourth class; the fifth he has left for us to surmise, by which the things combined attain once more dissociation and disengagement. I infer that these are intended to be figurative expressions corresponding to those just mentioned, generation corresponding to being, the infinite to motion, the definite to rest, the combining principle to identity, and the dissociating principle to divergence. But if these last are not the same as the others, even so, considered either in that way or in this, his division into five different classes would still hold good.

Evidently someone anticipated Plato in comprehending this before he did, and for that reason dedicated to the god an E as a demonstration and symbol of the number of all the elements.

Furthermore, observing that the Good displays itself under five categories, ⁵ of which the first is moderation, the second due proportion, the third the mind, the fourth the sciences and arts and the true opinions that have to do with the soul, and the fifth any pleasure that is pure and unalloyed with pain, at this point he leaves off, thus suggesting the Orphic verse ⁶

Bring to an end the current of song in the sixth generation.

[15] But as for its greatest excellency, I fear, lest being spoken it should press our Plato as much as he himself said Anaxagoras was pressed by the name of the moon, when he made a certain opinion concerning her illuminations, which was very ancient, to be an invention of his own. For has he not said this in his dialogue entitled Cratylus? ¹

Yes indeed, answered Eustrophus; but I see not any thing that has fallen out like it. And yet you know, that in the Sophister ² he demonstrates five principal beginnings, to wit, that which is, or Ens ( τὸ ὄν), the Same, the Different, adding to these, for a fourth and fifth, Motion, and Rest. Again, in his dialogue called Philebus, ³ using another manner of division, he says, that there is one thing Infinite, and another the End; and that all generation consists of these two mixed together. Then he puts the cause by which they are mixed for the fourth kind; and has left us to conjecture the fifth, by which the things that were mixed have again a division and dissipation. Now I am of opinion that these last are delivered as the images or representations of those before,—to wit, the things engendered of Ens, the Infinite of Motion, the End of Rest, the Mixing Principle of the Same, and the Separating Principle of the Different. But if these are different from those, yet both that way and this way these principles are still distinguished into five kinds and differences. Now some one, said he, being persuaded of these things and seeing them before Plato, consecrated to the God two E E, for a mark and symbol of the number of all things. And having perhaps further understood that good also appears in five kinds, of which the first is the mean, the second the commensurate, the third understanding, the fourth the sciences, arts, and true opinions in the soul, and the fifth a certain pleasure, pure and unmixed with sorrow; he stops there, subjoining that of Orpheus: