In his ethical works, Aristotle describes eudaimonia as the highest human good. In Book I of the Nicomachean Ethics he goes on to identify eudaimonia as the excellent exercise of the intellect, leaving it open whether he means practical activity or intellectual activity. With respect to practical activity, in order to exercise any one of the practical excellences in the highest way, a person must possess all the others. Aristotle therefore describes several apparently different kinds of virtuous person as necessarily having all the moral virtues, excellences of character.
- Being of "great soul" (magnanimity), the virtue where someone would be truly deserving of the highest praise and have a correct attitude towards the honor this may involve. This is the first such case mentioned in the Nicomachean Ethics.
- Being just in the true sense. This is the type of justice or fairness of a good ruler in a good community.
- Phronesis or practical wisdom, as shown by good leaders.
- The virtue of being a truly good friend.
- Having the nobility kalokagathia of a gentleman.
Aristotle also says, for example in NE Book VI, that such a complete virtue requires intellectual virtue, not only practical virtue, but also theoretical wisdom. Such a virtuous person, if they can come into being, will choose the best life of all, which is the philosophical life of contemplation and speculation.
Aristotle claims that a human's highest functioning must include reasoning, being good at what sets humans apart from everything else. Or, as Aristotle explains it, "The function of man is activity of soul in accordance with reason, or at least not without reason." He identifies two different ways in which the soul can engage: reasoning (both practical and theoretical) and following reasoning. A person that does this is the best because they are fulfilling their purpose or nature as found in the rational soul, similar to how the best horse in a chariot race is the fastest horse etcetera.
- (The wise person will) be more than human. A man will not live like that by virtue of his humanness, but by virtue of some divine thing within him. His activity is as superior to the activity of the other virtues as this divine thing is to his composite character. Now if mind is divine in comparison with man, the life of the mind is divine in comparison with mere human life. We should not follow popular advice and, being human, have only mortal thoughts, but should become immortal and do everything toward living the best in us. (NE 10.7)
In other words, the thinker is not only the 'best' person, but is also most like God.