Most of us pursue pleasure, wealth, or honour. Aristotle does not dismiss these goods. But he argues they are not final ends — they are pursued for the sake of something else. Only eudaimonia is desired for its own sake and never as a means to anything further.
Every craft, inquiry, and action aims at some good. Aristotle asks: what is the function specific to human beings? It cannot be mere life — plants have that. It cannot be perception — animals have that. It must be rational activity. The good for humans, then, is rational activity performed excellently.
This argument has been contested for centuries: does the assumption of a human function commit a naturalistic fallacy? But even critics acknowledge its clarifying power. By grounding ethics in what we distinctively are, Aristotle makes ethics inseparable from the question of human nature.
Virtues are stable dispositions — hexeis — lying between deficiency and excess. Courage lies between cowardice and recklessness. Generosity between miserliness and profligacy. The virtuous person does not merely act rightly but feels the appropriate emotions and takes pleasure in good action.
The term eudaimonia resists direct translation. "Happiness" implies subjective feeling; "flourishing" implies growth. Aristotle means something closer to living and faring well — a life that is objectively excellent when assessed from the outside.