All ten Books, from the function argument to the contemplative life.
The ten books are continuous argument, not separate essays. Books I–II set the foundations: eudaimonia, the function argument, virtue as habit. Books III–V work through the moral virtues in detail: courage, temperance, generosity, magnificence, magnanimity, justice. Books VI–VII turn to intellectual virtue and the puzzle of weakness of will. Books VIII–IX are the sustained treatise on friendship. Book 10 returns to pleasure and the question of the highest life. Read sequentially — Aristotle assumes you have followed.
Eudaimonia, the function argument, virtue as habit and the doctrine of the mean.
Book 1 introduces the question and the method. All action aims at some good; the highest good is eudaimonia. The function argument establishes what eudaimonia consists in: the activity of the soul in accordance with virtue, over a complete life. Pleasure, wealth, and honor are surveyed and found insufficient.
Book 2 introduces moral virtue as habit, distinguishes it from intellectual virtue, and gives the doctrine of the mean. Virtue is the median between excess and deficiency, found not by formula but by experience. Character is measured by the pleasures and pains one takes in virtuous action.
Courage, temperance, generosity, magnanimity, justice — worked through one by one.
Book 3 establishes the theory of voluntary action and moral responsibility, then applies it to the first two virtues: courage (facing death in the right way, for the right reasons) and temperance (the proper mean with respect to bodily pleasures). Both are worked through in detail as instances of the general doctrine.
Book 4 works through the moral virtues beyond courage and temperance: generosity, magnificence, magnanimity (the most contested), proper ambition, tempered anger, wit, and truthfulness. Each is the mean between its characteristic excess and deficiency. The portrait of the great-souled person is Aristotle's most vivid and most divisive.
Book 5 gives the treatise's full account of justice: general justice (complete virtue toward others) and particular justice (distributive and corrective). Distributive justice is proportionate equality; corrective justice restores the arithmetic mean. The book ends with equity — the correction of law's generality by attention to the particular case.
Practical wisdom, the intellectual virtues, and the puzzle of akrasia.
Book 6 introduces the intellectual virtues: scientific knowledge, technical skill, practical wisdom (phronesis), intuitive understanding, and philosophical wisdom. Phronesis is the decisive one for moral life — the disposition to deliberate well about what is good for human beings and to act on it. It requires experience and cannot be learned young.
Book 7 examines akrasia (weakness of will) — the phenomenon Socrates thought impossible. Aristotle argues it is real: the akratic person acts against their own better judgment under the influence of passion. The second half offers an account of pleasure as the unimpeded exercise of a faculty in its proper condition.
Three kinds of friendship — and why friendship of virtue is the precondition of the good life.
Book 8 distinguishes three kinds of friendship — utility, pleasure, and virtue — and argues that only the third is friendship in the complete sense. It is rare, slow to form, and durable: good people love each other for what they are. The book also examines friendships between unequal parties and the political dimension of concord.
Book 9 examines self-love, the dissolution of friendships, the question of how many genuine friends one can have, and the argument that even the happy person needs friends. The deepest claim: we need friends for self-knowledge — the virtuous friend is the mirror in which we see ourselves.
Pleasure revisited, and the contested conclusion: is the best life contemplative or active?
Book 10 revisits pleasure — not a process but an activity, the unimpeded exercise of a faculty — and then answers the treatise's culminating question. The highest life is the contemplative, but the life of moral virtue is the distinctively human second-best. The book ends with the hand-off to the Politics: the good of the individual is realised only inside a good community.