From the letter of Blessed Humbert of Romans On Regular Observance (Opera de Vita Regulari). This is the alternative Second Reading for the Office of Readings on the Memorial of Bl Mannes, the brother of St Dominic (18 August). This is from the Daily Office propers of the Order of Preachers.
A brother should never pass over in silence what needs to be said, nor say what should not be spoken. When a brother intends to speak, let him first consider his words in his heart that he may express honorably, moderately, truthfully and kindly what it is he wishes to say. For the tongue is deceitful, puffed up, inflamed with duplicity, and hateful to God and humankind.
Dearly beloved, consider carefully what you say, to whom, when or where, how or how much, and certainly why you say it. Otherwise, if the proper circumstances are lacking, your speech may give rise to a bad conscience in your own heart or to scandal in the heart of your hearer. You should aim for three things in your speech – gesture, voice, and meaning. Let your gestures be controlled, your voice well-modulated, your meaning always true.
Do not do battle with words, nor worry about gaining victory in disputes. Always avoid words which are damaging to the speaker or to the listener. One should keep away from speech which is not a credit to the one who speaks, or to the one who listens, or to the one about whom a person speaks.
Consider also the time for speaking, because at times one should keep silent and at other times something should be said. There is never a time when evil should be uttered; sometimes even good things should not be mentioned. When another has begun to speak, we should be silent, lest we appear to interrupt what the person has to say. When we sense that our audience is not prepared for what we have to say, we should refrain from speech. At times we should keep silence to avoid loquaciousness or because we have not yet formulated in a suitable manner what we wish to say, or even because the words that we have decided to you are no longer appropriate to the conversation.
Let the elderly speak of the wisdom of reflection, the young of a readiness for work, the wise of the mystery of the Scriptures, the simple of examples of good works, those concerned with business of the needs of the active life, those living quietly of the sweetness of the contemplative life, prelates of the management of temporal and spiritual goods, subjects of obeying commands.
When we wish to speak for our own building up, let us choose how we can bring others to Virtue, and by what teaching. When we speak for the building up of others, let us turn to those things that we hope to correct in ourselves through our exhortation. Furthermore, let our teaching tend toward this goal: to urge the timid to constancy, the proud to fear, the bold to reflection, the lukewarm to fervor, the boisterous to silence, the speechless to a word of exhortation, the impatient to gentleness, the careless to vigilance, the cruel to forbearance, the hasty and demanding to restraint.
In addition take care that when a brother speaks, he not move about inappropriately, nor destroy the charm of his speech by glancing about or making faces.
May you avoid every word that is bitter, proud, disparaging, flattering, vicious, sworn by oaths, superfluous, or careless. As you ought not speak ill of those who are absent, so you should not laugh at those who are present. Do not jest with those who are senseless, nor envy the learned.
Keep silent about trivialities; speak about what will bear fruit. In your conversation do not keep your heart on your tongue, but rather check your tongue with your heart. Surely when you come to speak, you can offer a few words that are intelligible. Love quiet reflection; flee the business of the world. Through silence the heart is quieted, pain is avoided, peace is maintained, and the mind is raised more quickly to contemplation. The more you withdraw from the noise of business, the closer will God be to you.