Happiness, according to Aristotle, is the complete end of life. He uses the term Eudemonia to describe happiness, but more accurately, he is talking about human flourishing. Achieving such happiness requires a life aimed at excellences, both moral and intellectual, and is not realized until the final days of life. In other words, Aristotle's conception of happiness is not a feeling that arises one day and is gone by the next. It's the telos, the end goal, of life.
Aristotle lays out his framework for human flourishing, happiness, in his Nicomachean Ethics. Fully grasping his framework requires careful study. I have only read it once, which with any work of Aristotle's does not count as careful study. Nonetheless, what follows is a snippet—some notes, really—of what I understand regarding the necessity of moral excellences to complete life happy, flourishing. And what ought to be a part of a robust education.
For Aristotle, happiness is the chief good and desirable for its own sake, not for the sake of something else.
"Since there are evidently more than one end, and we choose some of these (e.g., wealth ...) for the sake of something else, clearly not all ends are complete ends; but the chief good is evidently something complete. ... we call that which is in itself worthy of pursuit more complete than that which is worthy of pursuit for the sake of something else, and that which is never desirable for the sake of something else more complete than the things that are desirable both in themselves and for the sake of that other thing, and therefore we call complete without qualification that which is always desirable in itself and never for the sake of something else."
Happiness is held to be a complete end because "for this we choose always for itself and never for the sake of something else, but honour, pleasure, reason, and every excellence we choose indeed for themselves ..., but we choose them also for the sake of happiness, judging through them we shall be happy."
And happiness is not only complete, it is self-sufficient.
"[T]he complete good is thought to be self-sufficient." By self-sufficient, Aristotle does "not mean that which is sufficient for a man by himself, for one who lives a solitary life, but also for parents, children, wife, and in general for his friends and fellow citizens, since man is sociable by nature. ... Happiness, then, is something complete and self-sufficient, and is the end of action." It is realized through "complete excellence but also a complete life. ... [E]xcellent activities or their opposites are what determine happiness or the reverse."
Aristotle considers happiness a first principle, "for it is for the sake of this that we all do everything else." And achieving happiness, along with moral excellence, is an activity of the soul, which comes about as a result of habit.
Aristotle describes three kinds of things found in the soul: passions, faculties, states.
By passions he means "appetite, anger, fear, confidence, envy, joy, love, hatred, longing, emulation, pity, and in general the feelings accompanied by pleasure and pain; by faculties the things in virtue of which we are said to be capable of feeling these, e.g. becoming angry or being pained or feeling pity; by states the things in virtue of which we stand well or badly with reference to the passions, e.g. with reference to anger we stand badly if we feel it violently or too weakly, and well if we feel it moderately; and similarly with reference to the other passions."
The excellences are neither passions nor faculties, they are states: "[T]he excellence of man also will be the state which makes a man good and which makes him do his own work well."
Furthermore, Aristotle claims, "none of the moral excellences arise in us by nature. ... [W]e are adapted by nature to receive them, and are made perfect by habit." We learn to be excellent by doing what excellent men and women do. Every day. Throughout life. Just like craftsmen, he argues, are not born good or bad at their craft, the same is true of moral excellences: they must be practiced to ultimately become habits.
"It makes no small difference, then, whether we form habits of one kind or of another from our very youth; it makes a very great difference, or rather all the difference."
The three core moral excellences Aristotle puts forth as paths to happiness are temperance, courage, and justice, while states like vice, incontinence, and brutishness are to be avoided.
According to Aristotle, moderation is the key to realizing a given excellence. "[A] master of any art avoids excess and defect, but seeks the intermediate and chooses this—the intermediate not in the object but relative to us." For example, excess and defect destroy a work of art, while "the mean preserves it. ... [E]xcellence is a kind of mean, since it aims at the intermediate" of passions and actions. With fear and confidence at opposite ends of a spectrum, courage is the intermediate, and with pleasures and pains at opposite ends, temperance is the intermediate. Self-indulgence, for example, is an excess.
Aristotle cautions that excellence is not a state easily reached. As with art, excellence is "always concerned with what is harder; for even the good is better when it is harder." As stated before, it requires ongoing practice: "it is by doing just acts that the just man is produced, and by doing temperate acts the temperate man; without doing these no one would have even a prospect of becoming good."
Unfortunately, "most do not do these, but take refuge in theory and think they are being philosophers and will become good in this way, behaving somewhat like patients who listen attentively to their doctors, but do none of the things they are ordered to do. As the latter will not be made well in body by such a course of treatment, the former will not be made will in soul by such a course of philosophy."