The heaven of Venus may be compared to Rhetoric because of two properties: one is the brightness of its aspect [...]; the other is its appearance now in the morning, now in the evening.

And these two properties are found in Rhetoric: for Rhetoric is sweeter than all of the other sciences [...]; and it appears in the morning when the rhetorician speaks before the face of his hearer, and it appears in the evening (that is, behind) when the rhetorician speaks through writing, from a distance.

Convivio II, XIII, 13-14