1. You have sent a letter to me through the hand of a “friend” of yours, as you call him. And in your very next sentence you warn me not to discuss with him all the matters that concern you, saying that even you yourself are not accustomed to do this; in other words, you have in the same letter affirmed and denied that he is your friend. 2. Now if you used this word of ours in the popular sense, and called him “friend” in the same way in which we speak of all candidates for election as “honourable gentlemen,” and as we greet all men whom we meet casually, if their names slip us for the moment, with the salutation “my dear sir,”—so be it. But if you consider any man a friend whom you do not trust as you trust yourself, you are mightily mistaken and you do not sufficiently understand what true friendship means. Indeed, I would have you discuss everything with a friend; but first of all discuss the man himself. When friendship is settled, you must trust; before friendship is formed, you must pass judgment. Those persons indeed put last first and confound their duties, who, violating the rules of Theophrastus, judge a man after they have made him their friend, instead of making him their friend after they have judged him. Ponder for a long time whether you shall admit a given person to your friendship; but when you have decided to admit him, welcome him with all your heart and soul. Speak as boldly with him as with yourself. 3. As to yourself, although you should live in such a way that you trust your own self with nothing which you could not entrust even to your enemy, yet, since certain matters occur which convention keeps secret, you should share with a friend at least all your worries and reflections. Regard him as loyal, and you will make him loyal. Some, for example, fearing to be deceived, have taught men to deceive; by their suspicions they have given their friend the right to do wrong. Why need I keep back any words in the presence of my friend? Why should I not regard myself as alone when in his company?
4. There is a class of men who communicate, to anyone whom they meet, matters which should be revealed to friends alone, and unload upon the chance listener whatever irks them. Others, again, fear to confide in their closest intimates; and if it were possible, they would not trust even themselves, burying their secrets deep in their hearts. But we should do neither. It is equally faulty to trust everyone and to trust no one. Yet the former fault is, I should say, the more ingenuous, the latter the more safe. 5. In like manner you should rebuke these two kinds of men,—both those who always lack repose, and those who are always in repose. For love of bustle is not industry,—it is only the restlessness of a hunted mind. And true repose does not consist in condemning all motion as merely vexation; that kind of repose is slackness and inertia. 6. Therefore, you should note the following saying, taken from my reading in Pomponius: “Some men shrink into dark corners, to such a degree that they see darkly by day.” No, men should combine these tendencies, and he who reposes should act and he who acts should take repose. Discuss the problem with Nature; she will tell you that she has created both day and night. Farewell.
Seneca Lucilio suo salutem.
 Epistulas ad me perferendas tradidisti, ut scribis, amico tuo; deinde admones me ne omnia cum eo ad te pertinentia communicem, quia non soleas ne ipse quidem id facere: ita eadem epistula illum et dixisti amicum et negasti. Itaque si proprio illo verbo quasi publico usus es et sic illum amicum vocasti quomodo omnes candidatos ‘bonos viros’ dicimus, quomodo obvios, si nomen non succurrit, ‘dominos’ salutamus, hac abierit.  Sed si aliquem amicum existimas cui non tantundem credis quantum tibi, vehementer erras et non satis nosti vim verae amicitiae. Tu vero omnia cum amico delibera, sed de ipso prius: post amicitiam credendum est, ante amicitiam iudicandum. Isti vero praepostero officia permiscent qui, contra praecepta Theophrasti, cum amaverunt iudicant, et non amant cum iudicaverunt. Diu cogita an tibi in amicitiam aliquis recipiendus sit. Cum placuerit fieri, toto illum pectore admitte; tam audaciter cum illo loquere quam tecum.  Tu quidem ita vive ut nihil tibi committas nisi quod committere etiam inimico tuo possis; sed quia interveniunt quaedam quae consuetudo fecit arcana, cum amico omnes curas, omnes cogitationes tuas misce. Fidelem si putaveris, facies; nam quidam fallere docuerunt dum timent falli, et illi ius peccandi suspicando fecerunt. Quid est quare ego ulla verba coram amico meo retraham? quid est quare me coram illo non putem solum?
 Quidam quae tantum amicis committenda sunt obviis narrant, et in quaslibet aures quidquid illos urit exonerant; quidam rursus etiam carissimorum conscientiam reformidant et, si possent, ne sibi quidem credituri interius premunt omne secretum. Neutrum faciendum est; utrumque enim vitium est, et omnibus credere et nulli, sed alterum honestius dixerim vitium, alterum tutius.  Sic utrosque reprehendas, et eos qui semper inquieti sunt, et eos qui semper quiescunt. Nam illa tumultu gaudens non est industria sed exagitatae mentis concursatio, et haec non est quies quae motum omnem molestiam iudicat, sed dissolutio et languor.  Itaque hoc quod apud Pomponium legi animo mandabitur: ‘quidam adeo in latebras refugerunt ut putent in turbido esse quidquid in luce est’. Inter se ista miscenda sunt: et quiescenti agendum et agenti quiescendum est. Cum rerum natura delibera: illa dicet tibi et diem fecisse se et noctem. Vale.
—Lucius Annaeus Seneca, Epistulae Morales ad Lucilium (III)