  Metochites’ student and intellectual heir, Nikephoros Gregoras (1293/94–1360/61), began his career as an astronomer and ended it as a theological controversialist. Some of his letters and a few passages of his Roman History touch upon philosophical subjects: especially noteworthy is the vehement criticism of Aristotle in the dialogue Phlorentius, ostensibly an account of the author’s debate with Barlaam of Calabria (c. 1290–1348) in 1331–1332. As Gregoras notes with disdain, Barlaam was well-versed in contemporary Latin scholasticism; but it was his knowledge in ancient Greek philosophy and mathematics (including astronomy) that aroused both admiration and hostility when he arrived at Constantinople in the 1320s. In his Solutions for George Lapithes he is largely concerned with defending Aristotle against accusations of inconsistency with Plato as well as with himself. In so doing he addresses issues of more profound importance than Gregoras does in his Solutions for Helena Palaiologina, which deal principally with problems of natural philosophy; but the Neoplatonic epistemology in Barlaam’s Solution 4 and especially his First Greek Letter, according to which scientific knowledge rests on innate “substantial principles” in our souls, which reflect the creative principles in the Divine Intellect, and thus indicate the true causes of the nature of things, is curiously inconsistent with the theory expounded in his Anti-Latin Treatises, which states that the universal principles in our souls, on which demonstrative arguments are based, are completely derived from the experience of particulars.