But if we are to say that it is usef not for the sake of this but for the sake of becoming good, practical wisdom will be of no use to those who are good; but again it is of no use to those who are not; for it will make no difference whether they have practical wisdom themselves or obey others who have it, and it would be enough for us to do what we do in the case of health; though we wish to become healthy, yet we do not learn the art of medicine.