An individual is just when each part of his or her soul performs its functions without interfering with those of other elements. In Book IV, after cobbling together his blueprint of the ideal republic, Socrates asks Glaucon where justice is to be found, but they agree they will have to search for it together.
But to do evil to anybody, including one's enemy was inconsistent with the most elementary conception of morality.
Restorative justice that fosters dialogue between victim and offender shows the highest rates of victim satisfaction and offender accountability. If justice requires equality only by default, it might seem to apply only in a narrow range of cases.
What, for example, of the Christian virtue of love or the secular virtue of benevolence? No more a socio-political egalitarian than Plato, Aristotle, or Augustine, he analyzes it as calling for proportional equality, or equity, rather than any sort of strict numerical equality, and as a function of natural right rather than of positive law.
Despite their different roles in procreation, child-bearing, giving birth, and nursing babies, there is no reason, in principle, why a woman should not be as intelligent and virtuous—including as just—as men, if properly trained.
This leads him in Leviathan, his masterpiece, to conclude that anything real must be material or corporeal in nature, that body is the one and only sort of reality; this is the philosophical position of materialistic monism, which rules out the possibility of any spiritual substance.
This principle of egalitarianism suggests that the fairest allocation is one that distributes benefits and burdens equally among all parties.
If A stands in a relationship of the right kind to B, then it becomes a matter of justice how A is treated relative to B, but it does not matter in the same way how A is treated relative to C who stands outside of the relationship. Kant distinguishes between natural or private justice, on the one hand, and civil or public justice, on the other.