Well-timed silence hath more eloquence than speech. – Martin Farquhar Tupper, “Of Discretion,” Proverbial Philosophy

And there is monologue disguised as dialogue, in which two or more men, meeting in space, speak each with himself in strangely tortuous and circuitous ways and yet imagine they have escaped the torment of being thrown back on their own resources. – Martin Buber (1878—1965), translated from German

Once a word has been allowed to escape, it cannot be recalled. – Horace

As a matter of fact, have you never noticed that most conversations are simply monologues delivered in the presence of a witness? – Margaret Millar, The Weak-Eyed Bat, 1942