Chapter VI.--On Filthy Speaking.
From filthy speaking we ourselves must entirely abstain, and stop the mouths of those who practice it by stern looks and averting the face, and by what we call making a mock of one: often also by a harsher mode of speech. "For what proceedeth out of the mouth," He says, "defileth a man,"  --shows him to be unclean, and heathenish, and untrained, and licentious, and not select, and proper, and honourable, and temperate. 
And as a similar rule holds with regard to hearing and seeing in the case of what is obscene, the divine Instructor, following the same course with both, arrays those children who are engaged in the struggle in words of modesty, as ear-guards, so that the pulsation of fornication may not penetrate to the bruising of the soul; and He directs the eyes to the sight of what is honourable, saying that it is better to make a slip with the feet than with the eyes. This filthy speaking the apostle beats off, saying, "Let no corrupt communication proceed out of your mouth, but what is good."  And again, "As becometh saints, let not filthiness be named among you, nor foolish talking, nor jesting, which things are not seemly, but rather giving of thanks."  And if "he that calls his brother a fool be in danger of the judgment," what shall we pronounce regarding him who speaks what is foolish? Is it not written respecting such: "Whosoever shall speak an idle word, shall give an account to the Lord in the day of judgment?"  And again, "By thy speech thou shalt be justified," He says, "and by thy speech thou shalt be condemned."  What, then, are the salutary ear-guards, and what the regulations for slippery eyes? Conversations with the righteous, preoccupying and forearming the ears against those that would lead away from the truth.
"Evil communications corrupt good manners,"
says Poetry. More nobly the apostle says, "Be haters of the evil; cleave to the good."  For he who associates with the saints shall be sanctified. From shameful things addressed to the ears, and words and sights, we must entirely abstain.  And much more must we keep pure from shameful deeds: on the one hand, from exhibiting and exposing parts of the body which we ought not; and on the other, from beholding what is forbidden. For the modest son could not bear to look on the shameful exposure of the righteous man; and modesty covered what intoxication exposed--the spectacle of the transgression of ignorance.  No less ought we to keep pure from calumnious reports, to which the ears of those who have believed in Christ ought to be inaccessible.
It is on this account, as appears to me, that the Instructor does not permit us to give utterance to aught unseemly, fortifying us at an early stage against licentiousness. For He is admirable always at cutting out the roots of sins, such as, "Thou shalt not commit adultery," by "Thou shalt not lust."  For adultery is the fruit of lust, which is the evil root. And so likewise also in this instance the Instructor censures licence in names, and thus cuts off the licentious intercourse of excess. For licence in names produces the desire of being indecorous in conduct; and the observance of modesty in names is a training in resistance to lasciviousness. We have shown in a more exhaustive treatise, that neither in the names nor in the members to which appellations not in common use are applied, is there the designation of what is really obscene.
For neither are knee and leg, and such other members, nor are the names applied to them, and the activity put forth by them, obscene. And even the pudenda are to be regarded as objects suggestive of modesty, not shame. It is their unlawful activity that is shameful, and deserving ignominy, and reproach, and punishment. For the only thing that is in reality shameful is wickedness, and what is done through it. In accordance with these remarks, conversation about deeds of wickedness is appropriately termed filthy [shameful] speaking, as talk about adultery and pæderasty and the like. Frivolous prating, too, is to be put to silence.  "For," it is said, "in much speaking thou shalt not escape sin."  "Sins of the tongue, therefore, shall be punished." "There is he who is silent, and is found wise; and there is he that is hated for much speech."  But still more, the prater makes himself the object of disgust. "For he that multiplieth speech abominates his own soul."