What is Aristotle school of thought on Happiness?

Answer 1

Eudaimonia was the concept Aristotle inhereted from his culture, which means roughly "human flourishing." It's an end-in-itself, something at the root of every list of action justifications. "I did it to be happy." Flourishing has a different sense from subjective ecstacy, or even sustained hedonistic pleasure. For Aristotle it comes about only after certain conditions are met, two of which are left up to fate; those two are having good health and having wealth (in the sense that you can't help getting a hereditary diease or prevent an earthquake from destroying your property). The other condition is that the eudaimon person must seek out virtues, such as courage, sincerity, friendliness. And all these follow Aristotle's Golden Mean; it is vicious to have either too much courage or too litte, to be either recklessly brave or a coward. And among the virtues, it is not enough that you behaviorally seem to follow them, such as a person known for his honesty who only does so because he fears the consequence of lies. One must do it because "it would be a lie otherwise" -- which is different from, even, saying "honesty is best". You can find Aristotle's account in, at least, the Nicomachean Ethics.

This return of the eudaimonia has spurred the virtue ethics division of ethics in the last 50 years. Geach, Anscombe, Foot, and Mcdowel probably have way more interesting things to say regarding what virtues are for us today, how we can individuate them, and how we could justify them to others who aren't aware of them. Since eudaimonia isn't the sort of thing that you can assign to yourself with certainty-- you may not know what it takes to truly live well, as a flourishing Oak tree does in the best conditions, though you may think you do.

Answer 2

Don't worry, be happy. Oh, wait, no... that's Bobby McFerrin. Oops.