Aristotle, Nicomachean Ethics
H. Rackham, Ed.

Political Justice is of two kinds, one natural, the other conventional. A rule of justice is natural that has the same validity everywhere, and does not depend on our accepting it or not. A rule is conventional that in the first instance may be settled in one way or the other indifferently, though having once been settled it is not indifferent: for example, that the ransom for a prisoner shall be a mina, that a sacrifice shall consist of a goat and not of two sheep; and any regulations enacted for particular cases, for instance the sacrifice in honor of Brasidas,¹ and ordinances in the nature of special decrees. [2] Some people think that all rules of justice are merely conventional, because whereas a law of nature is immutable and has the same validity everywhere, as fire burns both here and in Persia, rules of justice are seen to vary. [3] That rules of justice vary is not absolutely true, but only with qualifications. Among the gods indeed it is perhaps not true at all; but in our world,² although there is such a thing as Natural Justice, all rules of justice are variable. But nevertheless there is such a thing as Natural Justice as well as justice not ordained by nature; [4] and it is easy³ to see which rules of justice, though not absolute, are natural, and which are not natural but legal and conventional, both sorts alike being variable. The same distinction will hold good in all other matters; for instance, the right hand is naturally stronger than the left, yet it is possible for any man to make himself ambidextrous. [5]

The rules of justice based on convention and expediency are like standard measures. Corn and wine measures are not equal in all places, but are larger in wholesale and smaller in retail markets. Similarly the rules of justice ordained not by nature but by man are not the same in all places, since forms of government are not the same, though in all places there is only one form of government that is natural, namely, the best form. [6]

The several rules of justice and of law are related to the actions conforming with them as universals to particulars, for the actions done are many, while each rule or law is one, being universal. [7]

There is a difference between ‘that which is unjust’ and ‘unjust conduct,’ and between ‘that which is just’ and ‘just conduct.’ Nature or ordinance pronounces a thing unjust: when that thing is done, it is ‘unjust conduct’; till it is done, it is only ‘unjust.’ And similarly with ‘just conduct,’ a dikaioma （or more correctly, the general term is dikaiopragema, dikaioma denoting the rectification of an act of injustice）.

We shall have later⁴ to consider the several rules of justice and of law, and to enumerate their various kinds and describe them and the things with which they deal.