Justice in the individual is now defined analogously to justice in the state. The individual is wise and brave in virtue of his reason and spirit respectively: he is disciplined when spirit and appetite are in proper subordination to reason. He is just in virtue of the harmony which exists when all three elements of the mind perform their proper function and so achieve their proper fulfillment; he is unjust when no such harmony exists.
Plato, Henry Desmond Pritchard Lee (1987). “The Republic”