AETIUS. - Heretic of the 4th century. He was born, according to some, at Antioch and, according to others, in its vicinity, into a very modest family. Educated by Arian teachers, he had to earn by work the means of subsistence and of study: he was a tinker, a household servant, a goldsmith and a physician. While, as a goldsmith, he provided himself with a living, as a physician he helped the poor for free. He later became acquainted with the Peripatetics, frequented their schools, studied at Antioch with Paulinus and Leontius, at Anazarbus with Athanasius, at Tarsus with Antonius. Neglecting the sacred sciences, whose ignorance is harshly reproached to him by Socrates (Hist. eccles., II, 35; PG 67, 300), he cultivated above all dialectic, in which he became extremely expert. It was his supreme satisfaction to provoke his adversaries and then reduce them to silence with cogent and exceedingly subtle arguments. St. Epiphanius affirms that he set out his doctrine in 300 close-knit syllogisms and reports 47 of them.
Leontius, bishop of Antioch, ordained him deacon with the task of teaching in public. But the very bold ideas of A., who taught that "the Son is not like the Father, nor identical with the Father, in respect of the divinity" (Epiphanius, Hoeres, 76, n. 2; PG 42, 517), whence it was deduced that he was of another substance (ἐτέρας οὐσίας "heterousians") and, as created, drawn from nothing (ἐξ οὐκ ὄντων "exoucontians"), scandalized the people. He deposed him from his office; he took refuge with the Arian George, intruded bishop of Alexandria, until, in 358, Eudoxius, successor of Leontius, recalled him to Antioch. But his excessively reckless doctrines displeased the Arians themselves, who at the Third Council of Sirmium condemned him and had him exiled to Pepuza in Phrygia. In 359 A. took part in the Synod of Seleucia, where the Acacians set themselves squarely against him. The following year he was deposed from his diaconal rank and confined first to Mopsuestia in Cilicia and then to Amblada in Pisidia. In 361, under Julian the Apostate, he was consecrated bishop without a see. He died at Constantinople between 366 and 370.
From A. the adherents of rigid Anomoeanism and of the most radical Arianism were called Aetians. They were also called Eunomians, from Eunomius, a disciple of A. and bishop of Cyzicus.