Peter of Spain’s handling of authorities in his commentary on the isagoge of johannitius

The dicta from medical and philosophical authorities appearing in commentaries on the Isagoge of Johannitius may be classified according to the different roles they play in the exposition of the text. This paper establishes that the opinions of the philosophical and medico-philosophical authorities were used more frequently as the constituent elements of inferences, whereas the dicta of purely medical authorities were quoted straightforwardly as sententiae. An exception to this is Peter of Spain who does not follow any hierarchical organization of authorities; instead, he freely quotes Aristotle in opposition to the physicians as well as in support of them. These observations are explained with specific reference to Peter’s ideas on the relationship between medicine and philosophy.