Plutarch De Garrulitate 3

[3] And yet Nature has built about none of our parts so stout a stockade as about the tongue, ¹ having placed before it as an outpost the teeth, so that when reason within tightens the reins of silence, ² if the tongue does not obey or restrain itself, we may check its incontinence by biting it till it bleeds. For Euripides ³ says that disaster is the end, not of unbolted treasuries or storerooms, but of unbridled tongues. And those who believe that storerooms without doors and purses without fastenings are of no use to their owners, yet keep their mouths without lock or door, maintaining as perpetual an outflow as the mouth of the Black Sea, appear to regard speech as the least valuable of all things. They do not, therefore, meet with belief, ⁴ which is the object of all speech. For this is the proper end and aim of speech, to engender belief in the hearer; but chatterers are disbelieved even if they are telling the truth. For as wheat shut up in a jar ⁵ is found to have increased in quantity, but to have deteriorated in quality, so when a story finds its way to a chatterer, it generates a large addition of falsehood and thereby destroys its credit.

[3] And yet there is no member of human bodies that Nature has so strongly enclosed within a double fortification, as the tongue, entrenched within with a barricado of sharp teeth, to the end that, if it refuses to obey and keep silent when reason presses the glittering reins within, we should fix our teeth in it till the blood comes, rather than suffer the inordinate and unseasonable din. For, according to the saying of Euripides, And truly, I must tell you, that they who think that houses without doors, and purses without strings, are of no use to their masters, yet at the same time set neither fence nor door before their lips, but suffer a continual torrent of vain and idle discourse to flow through them, like the perpetual flux of water through the mouth of the Pontic sea, seem to me to have the least esteem for human speech of all men in the world. Whence it comes to pass that they never gain belief, which is the end of all discourse. For the main scope and intention of all men that speak is to ¹ gain a belief of what they utter with those that hear them; whereas talkative noise-makers are never believed, let them speak never so much truth. For as wheat, when crowded into a musty vessel, is found to exceed in measure, but to be unwholesome for use; so the discourse of a loquacious person swells and enlarges itself with lies and falsehood, but in the mean time it loses all force of persuasion.