  Besides monophysitism, Philoponus’ name is associated with the doctrine of tritheism. However, one needs to be aware of an important difference: Whereas monophysitism was a reputable and powerful theological movement in the Eastern church, tritheism was little more than a hostile label given to certain intellectuals who tried to make the mystery of the Trinity intelligible in philosophical language. Philoponus was one such intellectual who, again, resorted to Aristotelian terminology to clarify and settle the trinitarian dispute. Already in the Arbiter it was clear that Philoponus tended to understand the crucial term ‘hypóstasis’ as meaning something like ‘primary substance’ in the sense of Aristotle’s Categories, i.e. an individual organic being. The fragments of the very late treatise On the Trinity confirm this. Since hypóstasis is certainly not an accident of divinity, Philoponus argues, it must be the case that the three hypostáseis of the Trinity are three particular divine substances with distinct properties. Only on this assumption, too, is it reasonable to speak of the consubstantiality of the three Persons, for if there were only one divine substance, what sense would it make to speak of consubstantiality at all? When Basil and Gregory of Nyssa spoke of the Trinity as ‘one ousía, three hypostáseis,’ they were not, Philoponus continues, enunciating four primary substances, but used ‘substance’ (ousía) in the secondary, abstract sense of essence or universal nature. In accordance with Aristotle, Philoponus claims that universals exist only in the mind. Thus, the claim that there is only one God appears to be true of the unity constituted by the concept of divinity. In actual fact, there are three separate divinities, Father, Son, and Spirit. In order to fend off any reminiscences of pagan polytheism, Philoponus points out that unlike the individually differentiated gods of the pagans the three divinities of the Trinity are all of the same, single divine nature in the universal sense of ‘nature’.  It is important to keep in mind that so-called ‘tritheists’ like Philoponus would not have conceded that they thereby abandoned monotheism. Although Philoponus had his followers, trinitarian philosophy of this kind could hardly be palatable to anyone not committed before all else to Aristotle’s ontology. The so-called tritheists faced immediate and severe criticism, and Philoponus himself was condemned by the Council of Constantinople of 680–81. Only recently, his views seem to have received increased attention and appreciation among philosophically-minded historians of the Church (see Erismann (2008) and Zachhuber (2018)).    Philoponus is often celebrated for having been one of the very first thinkers to reconcile Aristotelian philosophy with Christianity. To some extent, this is true, but crucially, his contemporaries must have taken a different view. Pagan philosophers abhorred the way in which Philoponus used Christianity as a vantage point from which, in their opinion, he recklessly disturbed the harmony of the Greek philosophers, and Christian theologians could not but castigate his attempt to comprehend in Aristotelian terms what was for them, essentially, a profound spiritual mystery demanding belief just because it was philosophically unacceptable. 5. Influence   Despite arousing the disapproval of many of his contemporaries, both pagan and Christian, Philoponus’ immediate influence may have been considerable among fellow-monophysites in Egypt. The anathema of 681, however, made the further proliferation of his theological ideas impossible. Likewise, his arch-enemy Simplicius, also a pupil of Ammonius, submitted the Grammarian’s anti-eternalism almost immediately to thundering pro-Aristotelian criticism (in his commentaries on the De Caelo and the Physics, written sometime in the late 530s). It was that polemic which resounded through the ages; its shockwaves can still be felt in later thinkers like Thomas Aquinas (1224–1274) and Zabarella (1533–1589) who carefully examined, though in the end rejected, Philoponus’ anti-eternalist arguments.  Philoponus’ work was studied extensively by the Arabs, who referred to him as Yahyâ an-Nahwî or Yahyâ al-‘Asqalânî. Al-Kindi (ca. 800–870) in particular is heavily indebted to Philoponus for his own attack on eternalism. Later on in the West, the arguments against the eternity of the world also persuaded Bonaventure (1217–1274) and Gersonides (1288–1344), and impetus theory was reaffirmed by Buridan (1300–1361) and his pupil Oresme (1325–1382).  In the sixteenth century, the first editions and numerous translations (into Latin) of Philoponus’ commentaries and the treatise Against Proclus began to appear in print. Eventually, Philoponus’ criticism of Aristotelian dynamics in the Physics commentary was widely discussed and persuaded such diverse thinkers as Gianfrancesco Pico della Mirandola (1469–1533) and, for different reasons, Galileo Galilei (1564–1642). In a sense, Philoponus is a Renaissance figure avant la lettre. However, historically positioned at a half way point between the Classical period and the Renaissance, he symbolizes more than anything else the Western mind’s excruciatingly slow struggle for emancipation from Aristotelianism on the one hand and blind faith in Church dogma on the other.  6. ‘Explaining’ Philoponus   The greatest challenge for a student of this period of the history of philosophy is to understand how a phenomenon such as Philoponus could have occurred at all. To be sure, elusive individual qualities of his mind and personality must have played an essential rôle, but it is equally true that philosophical, social, and religious parameters are likely to have supplied conditions which allowed him to carry forward his unprecedented and unparalleled challenge to a widely accepted intellectual tradition.  In the past, scholars have readily pointed towards the presumed fact that Philoponus was first raised as a Christian who later came into privileged contact with Greek rationalism; it is supposed that this constellation catalyzed his stance of critical opposition and rejection. However, this explanation is far from satisfactory. Many Christians from birth both before and after Philoponus were similarly exposed to pagan philosophy without reacting in a comparable way.  Other scholars have suggested that Philoponus may have received orders from clerical superiors to write a refutation of Aristotelianism. Again others, especially with a view to the invention of the theory of impetus, have sought the roots of Philoponus’ intellectual emancipation in broad socio-economic changes which occurred in late antiquity, in particular the emancipation of slaves. In whichever way the epithet ‘Philoponus’ is eventually going to be explained, it seems certain that what essentially enabled Philoponus to operate both as a critic of Aristotelianism and as a constructive thinker in his own right was somehow tied up with a new understanding of what one ought to do when one is reading and interpreting the philosophical texts of Plato or Aristotle. Whereas Neoplatonists, especially since Proclus (412–485), tended to approach these ancient texts as a fabric of venerable signs pointing per se and in an infallible way to a higher reality and to the truth, Philoponus read them (as we do today) as indicators of the thoughts and intentions of fallible authors. His more measured hermeneutic approach allowed Philoponus to point out problematic tensions, inconsistencies, and glaring contradictions in the Aristotelian corpus, and to highlight instances of substantive disagreement between Plato and Aristotle. In contrast, the program of the Neoplatonic tradition he grew up in had been, largely, either to ignore such hermeneutical problems or explain them away in an effort to harmonize the rich and diverse tradition of pagan Greek philosophy. 