Plutarch Quaestiones Convivales 9.14.7

[7] To this discourse Ammonius, as he used to do, subjoined that verse of Xenophanes, and desired every one to deliver his opinion. And I, after a short silence, said: As Plato thinks by the name, as it were by tracks, to discover the powers of the Gods, so let us place in heaven and over heavenly things one of the Muses, Urania. And it is likely that those require no distracting variety of cares to govern them, since they have the same single nature for the cause of all their motions. But where are a great many irregularities and disorders, there we must place the eight Muses, that we may have one to correct each particular irregularity and miscarriage. There are two parts in a man’s life, the serious and the merry; and each must be regulated and methodized. The serious part, which instructs us in the knowledge and contemplation of the Gods, Calliope, Clio, and Thalia seem chiefly to look after and direct. The other Muses govern our weak part, which changes presently into wantonness and folly; they do not neglect our brutish and violent passions and let them run their own course, but by apposite dancing, music, song, and orderly motion mixed with reason, bring them down to a moderate temper and condition. For my part, since Plato admits two principles of every action, the natural desire after pleasure, and acquired opinion which covets and wishes for the best, and calls one reason and the other passion, and since each of these is manifold, I think that each requires a considerable and, to speak the truth, a divine direction. For instance, one faculty of our reason is said to be political or imperial, over which Hesiod says Calliope presides; Clio’s province is the noble and aspiring; and Polymnia’s that faculty of the soul which inclines to attain and keep knowledge (and therefore the Sicyonians call one of their three Muses Polymathia); to Euterpe everybody allows the searches into nature and physical speculations, there being no greater, no sincerer pleasure belonging to any other sort of speculation in the world. The natural desire to meat and drink Thalia reduceth from brutish and uncivil to be sociable and friendly; and therefore we say θαλιάζειν of those that are friendly, merry, and sociable over their cups, and not of those that are quarrelsome and mad. Erato, together with Persuasion, that brings along with it reason and opportunity, presides over marriages; she takes away and extinguisheth all the violent fury of pleasure, and makes it tend to friendship, mutual confidence, and endearment, and not to effeminacy, lust, or discontent. The delight which the eye or ear receives is a sort of pleasure, either appropriate to reason or to passion, or common to them both. This the two other Muses, Terpsichore and Melpomene, so moderate, that the one may only cheer and not charm, the other only please and not bewitch.