Justice

Book 5 opens by distinguishing two senses of justice. In its broadest sense, justice is the exercise of complete virtue toward others — the just person is simply the person who acts as the law requires, and good law requires virtuous action. In this sense justice is the most complete of virtues, not because it is itself all the virtues, but because it is their exercise directed at others rather than at oneself. Aristotle quotes Theognis: "In justice is all virtue summed." Injustice in this broad sense is lawlessness or the disposition to take more than one's share.

Particular justice is more specific. Distributive justice concerns the allocation of goods by the community: honor, money, whatever can be divided among citizens who share in a political order. The principle is proportionate equality — not that everyone gets the same, but that distribution corresponds to merit (though Aristotle acknowledges that democrats and oligarchs disagree about what merit means). Corrective justice concerns transactions, both voluntary (contracts) and involuntary (theft, assault): here the principle is arithmetic equality, and a judge's role is to restore the mean between the gain of one party and the loss of the other.

The book closes with two important refinements. First, the discussion of reciprocity in exchange: money functions as a common measure that makes incommensurable goods comparable, and just exchange is governed by proportionate reciprocity. Second, the treatment of equity: since law must speak in general terms, cases arise that the legislator did not foresee. Equity corrects the law in these cases, not by going against the law's intention but by supplying what the legislator would have said if present. The equitable person is not merely just but perceives when the general rule misses the particular case — a form of practical wisdom at work within the domain of justice.