For there is but one essential justice which cements society, and one law which establishes this justice. This law is right reason, which is the true rule of all commandments and prohibitions. Whoever neglects this law, whether written or unwritten, is necessarily unjust and wicked.
The rule of friendship means there should be mutual sympathy between them, each supplying what the other lacks and trying to benefit the other, always using friendly and sincere words.