 At the beginning of his philosophical career, Burley seems to have been attracted by Henry of Ghent’s theory rather than by the more radical one he was to support some thirty years later. As far as the constitutive and distinctive principles of the categories are concerned, however, in the middle commentary on the Categories Burley advances the same ideas that he defends in his final commentary. He thinks that what characterizes each category is its peculiar mode of being and that this is much more important than the differentiation of essences (TsP, ch. de substantia, ed. Conti, p. 29—the formulation of this thesis corresponds almost verbatim to that of the final commentary).