Francesco Filelfo, Letter to Lorenzo Medici (Part 21):
“Who, however, will deny after hearing these many things which we have laid out up to this point that there was a common Latin tongue which was for the orator not as much a source of admiration if he knew it as it was a source of mockery if he didn’t know it, since the people would think (as Crassus says) that he was not only not an orator, but scarcely even a person if he couldn’t speak it?
Therefore, we shouldn’t wonder if, in a language known to all, the whole theater shouted, ‘We know that it’s barbarous!’ if one syllable had been pronounced either too short or too long. For the habit of daily speech was to be preserved, which was a consensus of the educated, as we say that the mode of living which we should preserve is that decreed by the consensus of good people.”
Quis autem ex iis, quae non pauca in hunc usque locum perstrinximus, negare audeat latinum sermonem fuisse vulgarem, quem orator, si sciret, non tantae admirationi erat quantae, ubi nesciret, irrisioni, cum eum, ut dicebat Crassus, non oratorem modo, sed ne hominem quidem putarent esse?
Non igitur mirari oportebat si, in lingua omnibus cognita, theatra tota exclamabant “barbare scimus!”, si fuit una syllaba prolata aut brevior aut longior. Nam consuetudo quottidiani sermonis servanda erat, quae ita erat quidam eruditorum consensus, ut vivendi bonorum consensum dicimus.