Cumque plurimas et maximas commoditates amicitia contineat, tum illa nimirum praestat omnibus, quod bonam spem praelucet in posterum nec debilitari animos aut cadere patitur. verum enim amicum qui intuetur, tamquam exemplar aliquod intuetur sui. quocirca et absentes adsunt et egentes abundant et imbecilli valent et, quod difficilius dictu est, mortui vivunt; tantus eos honos, memoria, desiderium prosequitur amicorum. ex quo illorum beata mors videtur, horum vita laudabilis. quod si exemeris ex rerum natura benevolentiae coniunctionem, nec domus ulla nec urbs stare poterit, ne agri quidem cultus permanebit. id si minus intellegitur, quanta vis amicitiae concordiaeque sit, ex dissensionibus atque ex discordiis percipi potest. quae enim domus tam stabilis, quae tam firma civitas est, quae non odiis et discidiis funditus possit everti? ex quo quantum boni sit in amicitia iudicari potest.
(Cicero, De Amicitia 23)
Moreover, while friendship comprises the greatest number and variety of beneficent offices, it certainly has this special prerogative, that it lights up a good hope for the time to come, and thus preserves the minds that it sustains from imbecility or prostration in misfortune. For he, indeed, who looks into the face of a friend beholds, as it were, a copy of himself. Thus the absent are present, and the poor are rich, and the weak are strong, and–what seems stranger still–the dead are alive, such is the honor, the enduring remembrance, the longing love, with which the dying are followed by the living; so that the death of the dying seems happy, the life of the living full of praise. But if from the condition of human life you were to exclude all kindly union, no house, no city, could stand, nor, indeed, could the tillage of the field survive. If it is not perfectly understood what virtue there is in friendship and concord, it may be learned from dissension and discord. For what house is so stable, what state so firm, that it cannot be utterly overturned by hatred and strife? Hence it may be ascertained how much good there is in friendship. (tr. Andrew P. Peabody)