  The two positions that Bonaventure discusses are what we may call a broadly Aristotelian position, one eventually adopted by Thomas Aquinas, and a broadly Augustinian position advocated by Robert Grosseteste in his On light (De luce). According to the first, light is simply an accidental form, one found in degrees in different bodies, but according to the second, light is perhaps a substance or at least a substantial form communicating extension and visibility to physical things.