Aristotle's Nicomachean Ethics -

For Aristotle, the unique human function is the activity of the soul in accordance with reason .

Just as a knife is "good" if it cuts well, a human is "good" if they perform their unique function well. Aristotle's Nicomachean Ethics

True happiness is not a temporary emotion but a state achieved over a complete life. The Nature of Virtue (Arete) For Aristotle, the unique human function is the