"Sensibile positum supra sensum non facit sensum". Light and Medium in the "Synthesis" of James of Viterbo

The aim of this paper is to provide the analysis of the theory of light in James of Viterbo's Disputatio quarta de quolibet (quaestio 6), in order to place it in the context of medieval debate about the nature of light, by identifying and focusing on the main references of the Augustinian theologian, among whom expecially Bonaventure of Bagnoregio, Thomas Aquinas, Henry of Ghent, Godfrey of Fontaines and Giles of Rome have to be counted. This analysis reveals the originality of James's position, presented as via media, to say some sort of "synthetic solution" between the theory of the real existence and the theory of the intentional existence of light in the medium; it is also concerned with grasping and investigating the interesting relation of James's theory of light with his own theory of cognition, based on the conception of vision as prototypical sense as well as on the theory of the species.