Now, of that which is just as between citizens, part is natural, part is conventional. That is natural which has the same validity everywhere, and does not depend on our accepting or rejecting it; that is conventional which at the outset may be determined in this way or in that indifferently, but which when once determined is no longer indifferent; e.g. that a man’s ransom be a mina, or that a sacrifice consist of a goat and not of two sheep; and, again, those ordinances which are made for special occasions, such as the sacrifice to Brasidas [at Amphipolis], and all ordinances that are of the nature of a decree.

Now, there are people who think that what is just is always conventional, because that which is natural is invariable, and has the same validity everywhere, as fire burns here and in Persia, while that which is just is seen to be not invariable.