Book 9 continues Aristotle's inquiry into friendship by testing it where relationships are unequal, disputed, and changing. He begins with friendships between dissimilars, where proportion rather than identical exchange preserves the bond. The shoemaker's return is measured by worth, money supplies a common standard in civic life, but erotic friendships often collapse when lover and beloved want different things: pleasure on one side, utility on the other. When each loved incidental qualities rather than the person, the tie dissolves as soon as expectations fail, like the lyre player promised payment for pleasure while the patron thought he had already paid in enjoyment. Aristotle also asks who should set the value of a service, the giver or the receiver, and he notes that complaints arise most when extravagant promises are not fulfilled, while virtuous friendship gives without tallying debts like a commercial contract.
Hard cases follow about competing obligations. Should one always obey a father, or trust a doctor when ill and a general when war threatens? Should one repay a benefactor or help a friend when both cannot be served? Aristotle denies a single rule for every situation, but he says benefits should generally be returned before new favors are handed out, as loans are paid before fresh gifts. Yet context alters the answer: ransom, gratitude to parents, and urgent need all shift what justice requires. Mothers seem to be loved more than they love in some comparisons, and benefactors rank among those to whom we owe special return, though no payment can fully equal what parents or teachers confer. The same practical intelligence that governs virtue must weigh magnitude, nobility, and necessity rather than treating every claimant as equally entitled to the same share of one's life.
Aristotle then asks whether friendships should be broken when the other party changes. Utility and pleasure friendships may end naturally when usefulness or amusement disappears, though pretense about loving character deserves blame. If someone accepted as good becomes bad, one need not keep loving evil itself, yet friends capable of reform should be helped rather than abandoned at the first failure. When one friend outgrows another in virtue, full equality of friendship may be impossible, as with childish companionships that no longer share tastes; still, former intimacy deserves some allowance when the breach is not caused by extreme wickedness. Benefactors love beneficiaries more than they are loved in return, because to benefit resembles giving birth, and what we help bring into being we tend to cherish more than those who receive the benefit remember.
The chapter's deepest turn is self love. People abuse the term for those who hoard wealth, honors, and bodily pleasures, yet proverbs say a man is his own best friend and charity begins at home. Aristotle resolves the clash by distinguishing base self love from noble self love. The good person assigns himself what is finest, obeys reason as his true self, and therefore loves himself rightly while the vicious person gratifies appetite against his own good. That is why he may sacrifice wealth or even life for friends and country: he prefers nobility to competition goods, and when a friend gains wealth he secures the greater good within himself. A friend is another self, so the marks of friendship toward others extend from a man's relation to himself when that relation is virtuous.
Aristotle also asks whether the happy person needs friends. The self sufficient man seems to lack nothing, yet friendship is among the greatest external goods, and the good man needs others to benefit because doing well by friends is more noble than doing well by strangers. Solitude is unchosen even by the happy, since human nature is political. Friends are needed in adversity for help and in prosperity for shared noble action; their presence lightens grief and deepens joy, though the tactful friend avoids making sorrow worse by mourning excessively. One should summon friends readily to share good fortune but hesitate before burdening them with every misfortune. One should not seek boundless numbers of friends: utility ties are laborious in excess, pleasure needs only a little seasoning, and complete friendship is limited by the capacity to live together, rejoice and grieve intimately, and share thought. Love, as an excess of friendship, is ideally directed to one person; famous comradely friendships are usually between two.
Living together is the heart of friendship, not grazing in the same place like cattle. Friends must be conscious of each other's existence through shared discussion and activity, whether in sport, pleasure, or philosophy. Bad friends make each other worse by unstable shared vice, while good friends improve each other and take the mould of qualities they approve, whence the saying that noble deeds come from noble men. Aristotle closes the treatment of friendship and turns to pleasure, which will complete the Ethics by asking what sort of activity makes a human life happy.
