Ammonius Hermiae (c. 435/445 - 517/526 C.E.) was a Greek philosopher, and the son of Hermias, a fellow-pupil of Proclus. Around 475, Ammonius , who had studied with Proclus in Athens, returned to Alexandria and took the teaching position previously held by his father in the school of Horapollo. There, he taught most of the important Platonists of the late fifth and early sixth centuries, including Asclepius, John Philoponus, Simplicius, Olympiodorus, and Damascius.
Though he is known mainly for his commentaries on Aristotle, Ammonius was also distinguished in geometry and astronomy. He authored the first preserved version of the set of questions to be answered preliminary to the study of Aristotle, and contributed the thesis that Aristotle viewed God as the efficient as well as final cause of the world. Ammonius' harmonization of Aristotle with Plato on this point later influenced Arabic Aristotelians and, eventually, Thomas Aquinas. Ammonius introduced an Alexandrian tradition of commentary on Aristotle; from about 475 to 545 C.E., the schools of Alexandria and Athens produced an intensive collection of Aristotelian commentary. Simplicius, a pupil of Ammonius, took it back to Athens, and when Justinian closed the pagan school there in 529, to Persia. Sergius, a physician and Nestorian priest, carried Aristotelian commentary to the Christian schools of Syria, and Stephanus of Alexandria took it to Constantinople. Ammonius’ major commentaries, on the Categoriae and Analytica priora of Aristotle's Organon, were well-respected by medieval European scholars.
The exact dates of Ammonius’ life are not known, but they can be approximated from various references to him in documents and historical records. Ammonius' father, Hermeias, studied in Athens under Syrianus (from Alexandria, Head of School in Athens from 431/2), and returned home to Alexandria, where he taught Platonism in the school of Horapollo, alongside the principal curriculum in rhetoric. Ammonius' mother Aedesia, a relative of Syrianus, had initially been engaged to marry Proclus (a student of Syrianus who succeeded him as head in 437), but Proclus received a divine warning to avoid the match. From these facts, it can be deduced that Ammonius, second son of Hermeias and Aedesia, must have been born after about 435 and probably before 445. When Damascius (c. 460-after 532) wrote his Philosophical History in 526, Ammonius appears to have already died, but he was alive in 517, when his course on Aristotle's Physics was first published by Philoponus. Most of the biographical information about Ammonius' life comes from the History of Damascius, who greatly admired Aedesia for her piety and charity, and gave her eulogy while he was a young student of rhetoric at Horapollo's school. Hermeias died when Ammonius and his younger brother Heliodorus were small, and Aedesia was given a public stipend by the Alexandrians until her sons reached maturity. Damascius also gave a description of Aedesia and Hermeias' eldest child, who died at age seven. Aedesia accompanied her two surviving sons to Athens, where, at her suggestion, both studied with Proclus.
Aedesia and her sons must have returned to Alexandria before 475, when she died of old age. Ammonius took over his father's former position, giving lectures on philosophy at the school of Horapollo on Friday mornings. Sometime between 475 and 485, Damascius heard him lecture on Platonic philosophy; around 515, Olympiodorus heard him lecture on the Gorgias (Olympiodorus, in Gorg. 199, 8-10). Asclepius mentions lectures (or seminars: Sunousiai, in Met. 77, 4) on Plato and refers to an "exegesis" (in Met. 70, 31) of the Theaetetus. Ammonius was best known for his lectures on Aristotle, some of which are extant.
In the fifth century, Alexandria was the third See of Christendom, and unlike Athens, was an important center of Christian culture. The school founded by Horapollo, where Hermeias taught philosophy, was a center of Hellenic pagan learning and religion. Some students at the school were Christians, or converted to Christianity later. There is some debate over whether the thought of the Alexandrian Neoplatonists was influenced by Christian doctrines, or whether certain aspects of Neoplatonism were de-emphasized in order to appease the Christian authorities.
Following the revolt of Illus (484-488), who had allied himself with the corrupt pagan Pamprepius, the Patriarch Peter III Mongus (482-489) took harsh measures against the pagan community. Damascius reported that Ammonius made some kind of agreement with the Patriarch: “Ammonius, who was wickedly greedy and saw everything in terms of what profit he could make, concluded an agreement with the overseer of the dominant doctrine” (Damascius 118B Athanassiadi, with her Introduction, 30-1 and n. 37).
Scholars have long speculated on the nature of this agreement, and on the character of Ammonius. It has been suggested that Ammonius might have agreed to continue the alleged Alexandrian Neoplatonic practice of making the gods into one by merging the One into the Intellect (a view congenial to Christianity); or that he might have agreed to lecture only on Aristotle, and not on Plato, or agreed not to teach the Aristotelian doctrine of the eternity and divinity of the world; or that he may have betrayed the hiding places of colleagues and pupils. Scholars have concluded that evidence does not support the first three possibilities. The fact that Ammonius was the only major figure of Horapollo's school who was allowed to resume his teaching, and that Damascius condemned him for seeking profit from the agreement, suggests the possibility that he might have betrayed fellow pagans. Another speculation points to statements in which Ammonius appears to minimize the importance of the use of divine names in theurgy, and agrees with Porphyry's refusal to accept the efficacy of theurgy in purifying the intellect and bringing humanity closer to God. Since theurgy was very important to other Neoplatonists, it is possible that Ammonius made an agreement not to emphasize theurgic practice and pagan ritual in his school.
Proclus (412–485), one of the last major Greek philosophers and the teacher of Ammonius in Athens, systematized one of the most elaborate, complex, and fully developed Neoplatonic systems. He was extremely influential on later Christian (Greek and Latin) and Islamic thought. Damascius, known as "the last of the Neoplatonists," studied philosophy and science, under Hermias and his sons, Ammonius and Heliodorus. Much of the biographical information about Ammonius comes from his Philosphical History, or Life of Isidore.
From various references in philosophical writings, it is apparent that around 475, Ammonius , who had studied with Proclus in Athens, returned to Alexandria and took the teaching position previously held by his father in the school of Horapollo. There he taught most of the important Platonists of the late fifth and early sixth centuries, had among his students Asclepius, John Philoponus, Simplicius, and Olympiodorus. Damascius listened to Ammonius’ lectures, but later studied under Proclus’ successor, Isidore.
Though he is known mainly for his commentaries on Aristotle, Ammonius was also distinguished in geometry and astronomy. His commentaries drew a great deal from the lectures of Proclus. Ammonius is known for introducing an Alexandrian tradition of commentary on Aristotle, and for his authorship of the first preserved version of the set of questions to be answered preliminary to the study of Aristotle. He also used the example of the sea battle from Aristotle’s De Interpretatione 9 as one of three determinist arguments, along with the ‘Reaper’ and the argument from divine foreknowledge. 
Later Neoplatonism was not only a complete metaphysical philosophical system, but was strongly associated with pagan theology and religious practice. However, theurgic and religious elements and the complex Iamblichean and Proclan hierarchies of being are not prominent in the commentaries of the Alexandrian school. The Alexandrian emphasis on Aristotle has often been attributed to Christian pressure and attempts to compromise with the church. Modern scholarship, however, does not find a great difference in the fundamental philosophical outlook or the doctrines of the Athenian and Alexandrian schools, but suggests that the context in which the Aristotelian commentaries were written should be closely examined.
Ammonius’ commentary on Aristotle, especially his logical works, may have been intended as preparatory study for less advanced students, and a preliminary to the study of Plato. In such a context, it would not have been appropriate to go into the details of a complex Neoplatonic theology and metaphysics. It is also possible that Ammonius’ failure to refer to certain Neoplatonic doctrines means that he did not embrace a complete Neoplatonic metaphysical system. Ammonius made certain statements that exhibit a genuine commitment to a Neoplatonic stance in metaphysics, even if he may not have espoused a system as complex as that of Proclus.
An important contribution of Ammonius was the thesis that Aristotle viewed God as the efficient as well as final cause of the world. According to Simplicius (490–560), Ammonius devoted an entire book to arguing that God was both the final and efficient cause of both the movement and existence of the whole world, sublunar and supralunar. Simplicius states that this interpretation allowed Ammonius to harmonize Aristotle with Plato. Instead of adopting Proclus’ criticisms of Aristotle, Ammonius refuted them by interpreting five Aristotelian passages to show that Aristotle did, in fact, reason along the lines Proclus had indicated in his criticism. For example, according to Simplicius, Ammonius argued that in Aristotle’s Physics 2.3, 194b 29-32, that from which comes the origin of motion (i.e., God, the unmoved mover), is itself a productive cause. Ammonius also argued that “if, according to Aristotle, the power of any finite body is itself finite, clearly whether it be a power of moving or a power that produces being, then, just as it gets its eternal motion from the unmoved cause, so it must receive its eternal being as a body from the non-bodily cause” Ammonius' harmonization of Aristotle with Plato on this point later influenced Arabic Aristotelians and, eventually, Thomas Aquinas.
From about 475 to 545 C.E., the schools of Alexandria and Athens produced an intensive collection of Aristotelian commentary. Simplicius, a pupil of Ammonius who was inclined to Platonism, took it back to Athens, and when Justinian closed the pagan school in Athens in 529, to Persia. Sergius, a physician and Nestorian priest, carried Aristotelian commentary to the Christian schools of Syria, and Stephanus of Alexandria took it to Constantinople. During the fifth and early sixth centuries, a center of Christian Neoplatonism flourished in Gaza; some of its members had studied under Ammonius.
Most of Ammonius’ commentaries were recorded by the students who listened to his lectures. Ammonius himself wrote the large commentary on De Interpretatione for publication. Of his reputedly numerous writings, his commentaries on Plato and Ptolemy are lost, but the following works are extant:
A life of Aristotle, ascribed to Ammonius, but with more accuracy to John Philoponus, is often prefixed to editions of Aristotle. It has been printed separately, with Latin translation and scholia, at Leiden, 1621, at Helmstedt, 1666, and at Paris, 1850.
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