Guillelmus de Aragonia was known as a philosopher for his commentary on Boethius and his works on physiognomy, oneirology, and astronomy; he was also a physician, perhaps a personal physician to the king of Aragon. In a time of intellectual upheaval and civil strife, when nobility was on the verge of being defined with legal precision as it had not been since antiquity, Guillelmus taught that true nobility is an acquired habit, not an inborn quality. Guillelmus wrote "De nobilitate animi, " On Nobility of Mind, around 1280 1290. Working in the recently renewed Aristotelian tradition, he took...