Aristotle, Nicomachean Ethics
H. Rackham, Ed.

and becomes a tyrant; but the function of a ruler is to be the guardian of justice, and if of justice, then of equality. [6] A just ruler seems to make nothing out of his office; for he does not allot to himself a larger share of things generally good, unless it be proportionate to his merits; so that he labors for others, which accounts for the saying mentioned above,¹ that ‘Justice is the good of others.’ [7] Consequently some recompense has to be given him, in the shape of honor and dignity. It is those whom such rewards do not satisfy who make themselves tyrants. [8]

Justice between master and slave and between father and child is not the same as absolute and political justice, but only analogous to them. For there is no such thing as injustice in the absolute sense towards what is one's own; and a chattel,² or a child till it reaches a certain age and becomes independent, is, as it were, a part of oneself, and no one chooses to harm himself; [9] hence there can be no injustice towards them, and therefore nothing just or unjust in the political sense. For these, as we saw, are embodied in law, and exist between persons whose relations are naturally regulated by law, that is, persons who share equally in ruling and being ruled. Hence Justice exists in a fuller degree between husband and wife than between father and children, or master and slaves; in fact, justice between husband and wife is Domestic Justice in the real sense, though this too is different from Political Justice.7.

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,³ 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,⁴ 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 easy⁵ 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