I’ll enumerate the core arguments from book I, as I understand them, as follows:
I’ve taken a few liberties reinterpreting the main arguments, so don’t expect this to be a completely literal reading of what Aristotle believes. Certain points had to be teased out and elaborated, while anachronisms were dropped in favour of modern terms. Hopefully the length doesn’t pose too much of a problem. I'll post a deeper analysis soon.
1) All human activity that accords with reason is goal-directed and hierarchical
— 1.1) All rational activity is an attempt to achieve or avoid an end or state of affairs.
— 1.2) Ends are produced by rational activities or the consequences of those activities.
— 1.3) Ends are valued for their own sake or for the sake of something else, thus ends are “practical goods.”
— 1.4) Ends that result from activities are by nature more final than the actions that produced them.
—1.5) Hence all rational activities are ordered in terms of their finality in the scheme of practical goods.
—1.6) Therefore the highest or most final good is that for the sake of which everything else is done.
It might be important to note here that the supreme good for human beings is actually the responsibility of politics rather than ethics. So it’s important to remember when we’re speaking of eudaimonia that Aristotle has a much broader idea in mind than the mere happiness of particular individuals. In fact, he would say that eudaimonia is not even possible in a state that doesn’t aim to produce virtue in its citizens. Fortunately, it appears most industrialized nations are capable of cultivating virtue.
2) The supreme good for human beings is eudaimonia (flourishing, happiness, well-being, self-actualization, success, etc.)
— 2.1) There is general consensus that happiness is the most important good in human life.
— 2.2) However, there are many conceptions of happiness and numerous disagreements about what constitutes a happy life.
— 2.3) Some people believe that happiness is a matter of pleasure and enjoyment, but this view must be rejected. The main problem with this view is that the means of pleasure and satisfaction are undifferentiated. There is no necessary preference in the means of satisfaction beyond the mere fact that people find them satisfying. Thus if one person finds it pleasurable to torment another, why shouldn’t it be permitted? Hence immorality can easily be built into this kind of moral arrangement since no attempt can be made to discriminate between people’s desires (Aristotle didn't really elaborate his objection to hedonism, so consider this my own interpretation of what seems wrong with this view).
— 2.4) Some people believe that happiness is a matter of honour and recognition, but this view must also be rejected. The most obvious problem with this position is that honour is only awarded for distinction or excellence. Clearly, if people seek to be honoured for their virtue or moral of character, then honour must be a subordinate good.
— 2.5) Some people believe that happiness is a matter of wealth and prosperity, but this view must also be rejected. Wealth is only used to secure other goods, so clearly it cannot be a higher end.
— 2.6) Some people believe that happiness is a matter of unification with the divine, but this view must also be rejected. Under this view I include animism, paganism, mysticism, Platonism, and all forms of theism. The main objection to this view shouldn’t come as a surprise to a secular audience: tout court, there simply is no evidence or reasonable grounds for belief.
— 2.7) Other views of happiness lack consensus and defensible expertise and so require no further analysis.
3) The supreme good for human beings must be something final, self-sufficient, and completely satisfying
— 3.1) Following from 1.6, the supreme good for human beings is something final without qualification. There is only one final end without qualification, and this is the end for the sake of which everything else is done.
— 3.2) The supreme good for human beings is cyclical in nature. In other words, it is achieved recurrently in the cycle of a complete life, providing the structure, ground, and direction for all other activity.
— 3.3) The supreme good for human beings is self-sufficient and completely satisfying. Self-sufficiency implies an absence of dependence on other things. It involves reaching a point at which one can rest without yearning for something more; it is completely satisfying in this sense.
— 3.4) Eudaimonia corresponds to this description.
4) The supreme good for human beings is a rational activity of the soul (personality) in accordance with virtue
— 4.1) A thing has no reason to change unless it has a goal or activity to realize.
— 4.2) A thing exists for the sake of its function or for the sake of the work that it can achieve.
— 4.3) The function of a thing is defined by the characteristic activity that it performs.
— 4.4) The function of a thing is performed well or badly as a result of its distinctive qualities (virtues).
— 4.5) The goodness of a thing lies in the extent to which its qualities or virtues contribute to its function.
— 4.6) Conversely, the badness of a thing lies in the extent to which its qualities or virtues detract from its function.
— 4.7) Human beings exist in the changeable world, and thus they too must have a distinctive function.
— 4.8) Human beings are in possession of acquired (e.g., occupations) and natural functions.
— 4.9) Acquired functions are subordinate to natural functions since what is acquired cannot exist prior to what is natural.
— 4.10) Human beings have parts (e.g., eyes) that realize specific functions, thus it is incoherent for the whole to be without function.
— 4.11) The principle of reason displayed in action is the most distinctive function of human beings (i.e., contra nutritive, sentient).
— 4.12) Rational activity can be exercised in two ways: (1) within the faculty of reason, and (2) between faculties susceptible to reason.
— 4.13) Therefore all virtues corresponding to the principle of reason displayed in action compose the human function.
— 4.14) And thus, to be a good human is necessarily to carry out the human function well.
— 4.15) So, in conclusion, the supreme good for human beings is a rational activity of the soul (personality) in accordance with virtue.
5) The supreme good for human beings, as defined above, is coherent with other reliable beliefs about eudaimonia
—5.1) Practical goods are of three types: (1) goods of an external nature; (2) goods of the soul (personality); and (3) goods of the body.
—5.2) Goods of the soul (personality) are superior to external and bodily goods. This view is supported by the wise and the many.
—5.3) Eudaimonia has been rightly defined as a fortunate and joyful flow of life, whether or not it is constituted by health, pleasure, honour, wealth, material conditions, virtue, or some combination of these things.
—5.4) The idea that eudaimonia is a rational activity of the soul (personality) in accordance with virtue (4) is consistent with those who believe that happiness consists in virtue.
—5.5) The simple possession of virtue cannot be the correct view of eudaimonia since no good consequences follow from the mere potential for being virtuous. Thus, virtue must be realized in an activity that achieves the practical good.
—5.6) A life in accordance with virtue is inherently pleasant because one finds pleasure in those things that are deemed to be good. Thus one who values and loves virtue will necessarily find pleasure in its exercise and realization.
—5.7) Goods are of two kinds: (1) those that are pleasant by nature (e.g., beauty); and (2) those that are contrived by human desires.
—5.8) Virtue is pleasant by nature. Hence virtuous actions can never be performed without being accompanied by pleasure.
—5.9) Since virtuous actions express the highest good for human beings they must also be the most pleasurable of human activities.
—5.10) The highest good and the highest pleasure have been rightly defined as eudaimonia. Thus the highest good and the highest pleasure, understood as a virtuous activity displaying a rational principle, is in accord with popular beliefs about eudaimonia.