Again, whatever that be which a man holds to constitute existence, or for the sake of which he chooses to live, in that he wishes to pass his time together with his friends; and thus some drink together, others gamble, others practise gymnastics, or hunt, or study philosophy together⁠—in each case spending their time together in that which they love most of all things in life; for, wishing to live in common with their friends, they do those things and take part together in those things which, as they think, constitute life in common.

Thus the friendship of those who are not good comes to be positively bad; for, having no stability of character, they confirm each other in things that are not good, and thus become positively bad as they become more like one another. But the friendship of good men is good, and grows with their intercourse; and they seem to become better as they exercise their faculties and correct each other’s deficiencies: for each moulds himself to the likeness of that which he approves in the other; whence the saying, “From good men thou shalt learn good things.” 243