 In the background of this notion of acquiring a better psychic disposition by virtue of repeatedly performing certain activities, is (in addition to Aristotle’s Nicomachean Ethics) the ancient medical tradition. Accordingly, even the (immaterial) rational faculty of the soul can be positively affected, if those faculties of the soul which operate by virtue of corporeal organs (such as sense perception and imagination) are improved. This concerns, at the most basic level, the mixture of the temperaments, which is directly related to the nutritive faculty: the better one’s temperaments are in balance, the fewer are the negative influences by the body on the soul, and the more easily this human being will, hence, be able to use her rational faculty. On a slightly more complex level, this idea of balance or harmony as a means to purify the soul also concerns the realm of moral virtues. For while one’s character is fundamentally predisposed by her temperament, al-Farabi maintains that virtues can be trained and improved. Thus, just as keeping the bodily humors in check, being able to find the ‘golden mean’ in ethical matters usually prepares the ground for a swifter and less distracted application of one’s rational  faculty.[13]