[On the use of authority in medieval medicine: Aristotle, Galen and flying flies]

This study attempts to reflect on the role of authority in academic medicine during the lower Middle Ages. We chose a topic - the mechanisms of visual perception - that may have been potentially controversial in medieval classrooms, as the historical authorities Aristotle and Galen disagreed on this phenomenon. Whether conflict arose between authorities, and whether it necessitated reconciliation or explanation, are investigated in the light of the problem faced by the medieval physician who had to explain the vision of nonexistent objects. In our article we also reproduce six questiones composed by university physicians of the Studia in Sienna, Bologne and Montpellier, who dealt with the problem.