Seneca, Moral Epistle 47.2-3
“Am I talking like an Epicurean again? Well, the same thing is good for me as for you–I am not your friend unless whatever bothers you matters to me too. Friendship makes everything into a partnership between us. There’s nothing good or bad for individuals: life is lived in common. It isn’t possible for anyone who only pays attention to themselves to live happily, someone who turns everything into a question of their own convenience. You need to live for another, if you want to live for yourself
This sense of community, when safeguarded carefully and sacredly, this force that mixes people of all kinds together, and insists that there are certain rights of the whole human race, is also important for what we are talking about, the closer commonwealth of friendship we must nurture. One who has much in common with humanity, has everything in common with a friend.”
Iterum ego tamquam Epicureus loquor? Mihi vero idem expedit, quod tibi; aut non sum amicus, nisi quicquid agitur ad te pertinens, meum est. Consortium rerum omnium inter nos facit amicitia. Nec secundi quicquam singulis est nec adversi; in commune vivitur. Nec potest quisquam beate degere, qui se tantum intuetur, qui omnia ad utilitates suas convertit; alteri vivas oportet, si vis tibi vivere. Haec societas diligenter et sancte observata, quae nos homines hominibus miscet et iudicat aliquod esse commune ius generis humani, plurimum ad illam quoque, de qua loquebar, interiorem societatem amicitiae colendam proficit. Omnia enim cum amico communia habebit, qui multa cum homine.