Second-rate and commonplace people, being too uneducated to entertain themselves as they drink by using their own voices and conversational resources, put up the price of female musicians, paying them well for the hire of an extraneous voice - that of the pipe - and find their entertainment in its warblings.  But where the drinkers are men of worth and culture, you will find no girls piping or dancing or harping.  They are quite capable of enjoying their own company without such frivolous nonsense, using their own voices in sober discussion and each taking his turn to speak or listen - even if the drinking is really heavy.

Protagoras  347c-d
 

Our music was formally divided into several kinds and patterns.  One kind of song, which went by the name of a hymn, consisted of prayers to the gods; there was a second and contrasting kind which might well have been called a lament; paeans  were a third kind, and there was a forth, the dithyramb, as it was called, dealing, if I am not mistaken, with the birth of Dionysus.  Now these and other types were definitely fixed, and it was not permissible to misuse one kind of melody for another.  The competence to take cognizance of these rules, to pass verdicts in accord with them, and, in case of need, to penalize their infraction was not left, as it is today, to the catcalls and discordant outcries of the crowd, nor yet to the clapping of applauders; the educated made it their rule to hear the performances through in silence, and for the boys, their attendants, and the rabble at large, there was the discipline of the official’s rod to enforce order.  Thus the bulk of the populace was content to submit to this strict control in such matters without venturing to pronounce judgment by its clamors.

Afterward, in course of time, an unmusical license set in with the appearance of poets who were men a native genius, but ignorant of what is right and legitimate in the realm of the Muses.  Possessed by a frantic and unhallowed lust for pleasure, they contaminated laments with hymns and paeans with dithyrambs, actually imitated the strains of the flute on the harp, and created a universal confusion of forms.  Thus their folly led them unintentionally to slander their profession by the assumption that in music there is no such thing as a right and a wrong, the right standard of judgment being the pleasure given to the hearer, be he high or low.  By compositions of such a kind and discourse to the same effect, they naturally inspired the multitude with contempt of musical law, and a conceit of their own competence as judges.  Thus our once silent audiences have found a voice, in the persuasion that they understand what is good and bad in art; the old “sovereignty of the best” in that sphere has given way to an evil “sovereignty of the audience.”  If the consequence had been even a democracy, no great harm would have been done, so long as the democracy was confined to art, and composed of free men.  But, as things are with us, music has given occasion to a general conceit of universal knowledge and contempt for law, and liberty has followed in their train.  Fear was cast out by confidence in supposed knowledge, and the loss of it gave birth to impudence.  For to be unconcerned for the judgment of one’s betters in the assurance which comes of a reckless excess of liberty is nothing in the world but reprehensible impudence.

So the next stage of the journey toward liberty will be refusal to submit to magistrates, and on this will follow emancipation from the authority and correction of parents and elders; then, as the goal of the race is approached, comes the effort to escape obedience to the law, and, when that goal is all but reached, contempt for oaths, for the plighted word, and all religion.  The spectacle of the Titanic nature of which our old legends speak is reenacted; man returns to the old condition of a hell of unending misery.

Laws  700a-701c.
 

The overseers must be watchful against its insensible corruption.  They must throughout be watchful against innovations in music and gymnastics counter to the established order, and to the best of their power guard against them, fearing when anyone says that that song is most regarded among men “which hovers newest on the singer’s lips” [Odyssey  i. 351], lest it be supposed that the poet means not new songs but a new way of song and is commending this.  But we must not praise that sort of thing nor conceive it to be the poet’s meaning.  For a change to a new type of music is something to beware of as a hazard of all our fortunes.  For the modes of music are never disturbed without unsettling of the most fundamental political and social conventions.

Republic  424b-c.
 

 We said we did not require dirges and lamentations in words.
 We do not.
 What, then, are the dirge-like modes of music?  Tell me, for you are a musician.
 The mixed Lydian, he said, and the tense or higher Lydian, and similar modes.
 These, then, said I, we must do away with.  But again, drunkenness is a thing most unbefitting guardians, and so is softness and sloth.
 Yes.
 What, then, are the soft and convivial modes?
 There are certain Ionian and also Lydian modes that are called lax.
 Will you make any use of them for warriors?
 None at all, he said, but it would seem that you have left the Dorian and the Phrygian.
 I don’t know the musical modes, I said, but leave us the mode that would fittingly imitate the utterances and the accents of a brave man who is engaged in warfare or in any enforced business, and who, when he has failed, either meeting wounds or death or having fallen into some other mishap, in all these conditions confronts fortune with steadfast endurance and repels her strokes.  And another for such a man engaged in works of peace, not enforced but voluntary, either trying to persuade somebody of something and imploring him - whether it be a god, through prayer, or a man, by teaching and admonition - or contrariwise yielding himself to another who is petitioning him or teaching him or trying to change his opinions, and in consequence faring according to his wish, and not bearing himself arrogantly, but in all this acting modestly and moderately and acquiescing in the outcome.  Leave us these two modes - the enforced and the voluntary - that will best imitate the utterances of men failing or succeeding, the temperate, the brave - leave us these.
 Well, said he, you are asking me to leave none other than those I just spoke of.

Republic  398d-399c.
 

The sight in my opinion is the source of the greatest benefit to us, for had we never seen the stars and the sun and the heaven, none of the words which we have spoken about the universe would ever have been uttered.  But now the site of day and night, and the months and the revolutions of the years have created number and have given us a conception of time, and the power of inquiring about the nature of the universe.  And from this source we have derived philosophy, than which no greater good ever was or will be given by the gods to mortal man.  This is the greatest boon of sight, and of the lesser benefits why should I speak?  Even the ordinary man if he were deprived of them would bewail his loss, but in vain.  This much let me say however.  God invented and gave us sight to the end that we might behold the courses of intelligence in the heaven, and apply them to the courses of our own intelligence which are akin to them, the unperturbed to the perturbed, and that we, learning them and partaking of the natural truth of reason, might imitate the absolutely unerring courses of God and regulate our own vagaries.  The same may be affirmed to speech and hearing.  They have been given by the gods to the same end and for a like reason.  For this is the principal end of speech, whereto it most contributes.  Moreover, so much of music as is adapted to the sound of the voice and to the sense of hearing is granted to us for the sake of harmony.  And harmony, which has motions akin to the revolutions of our souls, is not regarded by the intelligent votary of the Muses as given by them with a view to irrational pleasure, which is deemed to be the purpose of it in our day, but as meant to correct any discord which may have arisen in the courses of the soul, and to be our ally in bringing her to harmony and agreement with herself, and rhythm too was given by them for the same reason, on account of the irregular and graceless ways which prevail among mankind generally, and to help us against them.

Timaeus  47a-e.

Edith Hamilton and Huntington Cairns (eds.), The Collected Dialogues of Plato Including the Letters  (New York: Pantheon Books, 1961), 340, 1294-95, 665-66, 643-44, 1174-75.