Besides defining absolute justice, it is also necessary to determine what form justice takes in social and political matters. Political justice may be said to exist where men share a common way of life that enables them to have all they require for self-sufficient existence as free and equal members of society, whether viewed in actual (arithmetical) or proportional terms (e.g., the citizens of an aristocracy are proportionally equal since their status and rights depend on individual merit, while the citizens of a democracy are arithmetically equal since every free citizen has the same rights and privileges).
Since it is the function of law to decide between the just and unjust, there can be no political justice where relations between men are not governed by law. Laws only exist because men can be guilty of injustice. Where it is possible for people to act unjustly among themselves, it is also possible for them to act unjustly toward each other. For this reason rule by a single man is bad. Rulers, as men, tend to consider their own interests before those of the state, and thus become tyrants. The law is the real ruler of any just state, since it is the source of its equality, and the true function of human rulers is to act as guardians of the law and justice.
There is another form of justice, different from though analogous to that which we have been discussing. This is domestic justice, often viewed as justice between father and child or master and slave. The main distinction between it and political justice is that the injustice of a ruler to his subjects is absolute, while that of a man to his children or slaves is relative. A man's dependent children or slaves are in a sense part of himself. Since no one deliberately chooses to injure himself, it is difficult in any circumstances to say that someone is being unjust to his children or slaves. Justice between husband and wife is the only true form of domestic justice, but even this is different in detail from that which is just in the political or social spheres.