Aeneas Silvius Piccolomini, de Educatione Liberorum XXIV:
“Although we approve the speech of an educated tongue more than the habit of a silent prince, yet we would not recommend that a boy speak without forethought; for, that which is said or done without planning and without judgment is unable to be beautiful. Unpremeditated speeches, not only of boys but even of men, are loaded with levity and carelessness, but considerate thought does not allow a speech to wander off track. Why should I speak about boys, when even those famous orators, Pericles and Demosthenes, often refused to address the public when they said that they were unprepared? But if someone should let boys speak extemporaneously, he is setting the situation up for excessive talk. I would not have to much license of speech granted to you as a boy. Timely silence is the mark of great wisdom, and it has often troubled more people to have spoken finely than to have remained silent. That which is held in silence can easily be drawn out, but that which you have spoken can in no way be revoked. As Horace says, ‘a word, once it takes flight, can never be recalled.”
At nos linguae quamvis eruditae sermonem magis quam taciturni principis morem probemus, non tamen inpraemeditatum loqui puerum commendamus; quod enim inconsulto ac temere dictum factumve sit, id pulchrum esse nequit. Inpraecogitati sermones, nedum puerorum, sed virorum quoque plurima levitate atque incuria referti sunt, considerata vero meditatio orationem vagari non sinit. Quid dicam de pueris, quando illustres oratores, Pericles atque Demosthenes, saepius alloqui populum recusarunt, quia imparatos se esse dicebant. Si quis vero ex tempore pueros dicere sinat, extremae causam garrulitatis instituit. Nolo tibi nimiam puero sermonis patere licentiam; magnae sapientiae tempestivum silentium est, et nonnumquam sermone praestantius plures dixisse quam tacuisse paenituit. Quod silentio retentum est, effertur facile; quod semel edideris, revocari nullo modo potest. ‘Nam semel emissum,’ Flacco testante, ‘volat irrevocabile verbum.’
We have several posts on this theme now! There is another medievalist: https://sententiaeantiquae.com/2016/09/15/silence-vs-speaking/
Then there is the famous bit from Plutarch: https://sententiaeantiquae.com/2016/01/21/when-in-silence-better-than-speech-plutarch-on-odysseus/
And another passage from Plutarch: https://sententiaeantiquae.com/2016/09/09/knowing-when-to-be-silent/
The next book should just be “When Not To Talk”!
You’re on to something! Hopefully we don’t receive a note from publishers about learning “When Not to Submit!” I like the idea, and it seems that the Two Ears One Mouth piece is always exceptionally popular.
Then there is this too:
“He who does not know how to be silent also does not know how to speak”
Qui nescit tacere, nescit et loqui. Seneca, Proverbia Senecae 132