  But it is undoubtedly with Photios that we first encounter in Byzantine times a large-scale revival of the study of antiquity and a profound interest in the texts of ancient philosophers. Photios is famous mainly for his Bibliotheke, a vast compilation of ancient Greek literature, and a Lexicon, in which he collected notable words and expressions. He also taught Aristotelian logic and wrote, for this purpose, a series of small essays on Aristotle’s Categories, which are included in the Amphilochia, an unsystematic collection of texts on theological and philosophical topics. In these and other essays, Photios engages in a critical discussion of some of the most central theses in ancient philosophy, such as Plato’s conception of forms, whose capacity to function as predicates he rejects, and Aristotle’s distinction between primary and secondary substances, which he thinks entails that ‘substance’ is an ambiguous term.