Justice is primarily a possible, but not a necessary, quality of a social order regulating the mutual relations of men. Only secondarily it is a virtue of man, since a man is just, if his behavior conforms to the norms of a social order supposed to be just. But what does it really mean to say that a social order is just? It means that this order regulates the behavior of men in a way satisfactory to all men, that is to say, so that all men find their happiness in it. The longing for justice is men's eternal longing for happiness. It is happiness that men cannot find alone, as an isolated individual, and hence seeks in society. Justice is social happiness. It is happiness guaranteed by a social order.
HANS KELSEN, What Is Justice?