But that which is just in private transactions 105 is indeed fair or equal in some sort, and that which is unjust is unfair or unequal; but the proportion to be observed here is not a geometrical proportion as above, but an arithmetical one.

For it makes no difference whether a good man defrauds a bad one, or a bad man a good one, nor whether a man who commits an adultery be a good or a bad man; the law looks only to the difference created by the injury, treating the parties themselves as equal, and only asking whether the one has done, and the other suffered, injury or damage.

That which is unjust, then, is here something unequal [or unfair] which the judge tries to make equal [or fair]. For even when one party is struck and the other strikes, or one kills and the other is killed, that which is suffered and that which is done may be said to be unequally or unfairly divided; the judge then tries to restore equality by the penalty or loss which he inflicts upon the offender, subtracting it from his gain.