The function of man is an activity in accordance with a certain arrangement or order in the soul (according to Aristotle). That is why Aristotle can conclude that the human good is an activity of soul in accordance with virtue: for virtue is a certain organization of the soul. How this order is instilled in man’s soul is a central issue of ethics. Of course, the exercise of the virtues will often involve man’s practical reason. But if the practical reasoning did not flow from a certain organization of the soul, it would be empty. In fact It is because a man’s life has a certain order that he is able to reason about it: the logos (or rational principle) in his mind will reflect the logos in his soul.
Jonathan Lear, Aristotle: The Desire to Know