But these terms, “loss” and “gain,” are borrowed from voluntary exchange. For in voluntary exchange having more than your own is called gaining, and having less than you started with is called losing (in buying and selling, I mean, and in the other transactions in which the law allows free play); but when the result to each is neither more nor less but the very same amount with which he started, then they say that they have their own, and are neither losers nor gainers. That which is just, then, is a mean between a gain and a loss, which are both contrary to the intention, 108 and consists in having after the transaction the equivalent of that which you had before it.

Some people, indeed, go so far as to think that simple requital is just. And so the Pythagoreans used to teach; for their definition of what is just was simply that what a man has done to another should be done to him.