Book 5 is Aristotle's full treatment of justice. He begins by distinguishing justice as a whole virtue, being lawful and fair toward others, from particular justice, which concerns gain and loss in exchanges among neighbors. The unjust person is grasping: he takes too much of what is good in itself, especially honor, money, and safety. General justice is almost complete virtue turned outward, because the lawful person does what the other virtues require in a shared life. Particular justice is narrower and more technical: it asks who got more or less than a fair share in a concrete dealing. Without that distinction, every moral failure looks like the same offense, and courts and neighbors lose the language they need to name the injury. Aristotle is writing for people who will vote, judge, trade, and punish, not only for people who want a beautiful definition.
Particular justice has two main forms. Distributive justice divides honors, money, and common goods among citizens according to desert, using geometric proportion: equal shares for equals, unequal for unequals, not mere arithmetic sameness. Give the same prize to unequal merit and you have not been fair; you have only been identical. Rectificatory justice corrects transactions between individuals. In voluntary exchanges such as buying, selling, and lending, the just price restores equality between what is given and received. In involuntary harms such as theft, assault, and fraud, the judge takes away the offender's gain and restores the victim, as if the scales were evened. The courtroom image matters: justice here is not warmth of feeling but a measured restoration of balance after a disturbance. A slap and a gift are not settled by the same formula, and Aristotle refuses to pretend they are. Distribution looks forward to desert; correction looks backward to a disturbed equality and asks what would put the parties level again.
Reciprocity in commercial life is not the same as either form, yet it holds society together. Builder and shoemaker must exchange in proportion to their work, which is why money exists as a conventional measure of demand. Without a common measure, association stalls; with one, unlike goods can meet without either party being cheated by crude barter. Money is a tool of fairness before it is a tool of greed, a shared language for unequal goods in trade. Political justice applies among free and law-governed equals. Relations of master and slave, or father and child, involve analogies of rule and care but not full civic justice, because the parties are not peers in the same political sense. Some justice is natural, the same everywhere in force; some is legal and varies by constitution, like measures that differ between wholesale and retail markets. Custom and nature both shape what a city calls just, and Aristotle refuses to collapse them into one slogan about either eternal sameness or pure local whim. A constitution can rearrange legal justice; it cannot invent the force of natural claims out of nothing.
Justice is a mean between having too much and too little of what can be shared; injustice is excess and defect. Not every harmful act is fully unjust in character. Mistakes done in ignorance differ from deliberate wrongs done by choice, though angry acts may be unjust without making the agent wicked overall. The difference between a stumble and a chosen grab is the difference between pardon and blame. Aristotle also asks hard questions: can someone be willingly wronged, or wrong himself? Suicide harms the city. Strict puzzles about harming yourself aside, complete self-injustice in the political sense is impossible because justice always involves more than one party. You cannot be just or unjust alone in the full civic meaning of the word. Fairness is relational by definition. That is why the self-help fantasy of being just to yourself alone never satisfies Aristotle's political account.
Equity corrects law when universal rules misfire in particular cases. Aristotle's image is the flexible ruler used in Lesbian stonework that bends to the surface rather than forcing a curved wall into a straight line. The equitable person chooses what the legislator would have intended, pardoning human failings where the letter of the law would be too crude. That is not softness for its own sake; it is fidelity to the purpose of the law when a rigid reading would betray it. Equity is the repair kit for legislation that must speak universally and therefore sometimes miss the seam of a particular life. Acting unjustly is worse than suffering injustice, because it springs from vice; yet justice remains essentially human, since gods need no share of goods and the incurably vicious cannot benefit from them. With justice mapped across distribution, correction, exchange, civic equality, and equity, Aristotle prepares the next turn: from fairness among persons to the intellectual virtues that guide choice itself.
