Book 3.21

There are some things which the law neither enjoins nor forbids; it is in these that a slave finds the means of bestowing benefits. As long as we only receive what is generally demanded from a slave, that is mere service; when more is given than a slave need afford us, it is a benefit; as soon as what he does begins to partake of the affection of a friend, it can no longer be called service. There are certain things with which a master is bound to provide his slave, such as food and clothing; no one calls this a benefit; but supposing that he indulges his slave, educates him above his station, teaches him arts which free-born men learn, that is a benefit. The converse is true in the case of the slave; anything which goes beyond the rules of a slave's duty, which is done of his own free will, and not in obedience to orders, is a benefit, provided it be of sufficient importance to be called by such a name if bestowed by any other person.