A slave, according to the definition of Chrysippus, is a “hireling for life.” And, just as a hireling gives a benefit if he supplies more than he contracted to do, so a slave — when he exceeds the bounds of his station in goodwill toward his master, and surpasses the expectation of his master by daring some lofty deed that would be an honor even to those more happily born, a benefit is found to exist inside the household. Or do you think it fair that those with whom we become angry if they do less than they ought should not draw our gratitude if they do more than they ought or are wont? Do you want to know when what a slave does is not a benefit? When one might say of it: “What if he had refused?” But when he has bestowed something that he had a right to refuse to bestow, the fact that he was willing deserves to be praised.
Benefit and injury are the opposites of each other it is possible for a slave to give a benefit to his master if it is possible for him to receive an injury from his master. But cognizance of the injuries inflicted by masters upon their slaves has been committed to an official who restrains their cruelty and lust and their stinginess in supplying them with the necessities of life. What, then, is the case? Does a master receive a benefit from a slave? No, but a human being from a human being. After all, whatever was in his power, he did — he gave a benefit to his master; that you should not receive one from a slave is in your power. But who is so exalted that Fortune may not force him to have need of even the most lowly?