Friendship and justice deal with things and persons in the same way. Every community or association requires a conception of what is just between people and also involves some degree of mutual friendship, both conceived on the level that is required for people to live or work together in the way required by the particular kind of association.
Friendship is the true expression of community, though what is right and proper in one kind of friendship may not be appropriate in another. Intensification of the degree of friendship results in a concomitant intensification in degree in feelings of obligation between friends. Obligations in friendship are coextensive with obligations injustice.
All associations between men are part of the larger association known as the political community or state. Just as men combine or associate while traveling or farming for the sake of securing some advantage such as safety or the necessities of life, the political community originally came into being and has continued in existence to secure the advantage of its members. This is the goal toward which legislators aim, and for this reason justice is popularly defined as "the common interest."