Chapter V .— The Dispute of Arius with Alexander, his Bishop. After Peter, bishop of Alexandria, had suffered martyrdom under Diocletian, Achillas was installed in the episcopal office, whom Alexander succeeded, during the period of peace above referred to. He, in the fearless exercise of his functions for the instruction and government of the Church, attempted one day in the presence of the presbytery and the rest of his clergy, to explain, with perhaps too philosophical minuteness, that great theological mystery— the Unity of the Holy Trinity. A certain one of the presbyters under his jurisdiction, whose name was Arius, possessed of no inconsiderable logical acumen, imagining that the bishop was subtly teaching the same view of this subject as Sabellius the Libyan, 119 from love of controversy took the opposite opinion to that of the Libyan, and as he thought vigorously responded to what was said by the bishop. ‘If,’ said he, ‘the Father begat the Son, he that was begotten had a beginning of existence: and from this it is evident, that there was a time when the Son was not. It therefore necessarily follows, that he had his substance 120 from nothing.’ 119    Though Sabellius was the originator of one of the earliest and most plausible attempts at explanation of the mystery of the Trinity (for which see life of Sabellius in Smith and Wace, Dict. of Christian Biog. , and Hodge, System. Theol. Vol. I. p. 452, 459), nothing is known of him, not even why he is called a Libyan here (also by other ancient writers, e.g. Philastrius, de Hæres. 26, and Asterius, quoted by Phot. Biblioth. Cod. 27). Some say that he was a native and resident of Libya, others that he was an ecclesiastic appointed to some position there; nor is it known whether the Libya meant is the Libyan Pentapolis or the Pentapolitan Ptolemais. 120     ὑπόστασιν . Through the Arian controversy this word is used in its metaphysical sense of ‘real nature of a thing as underlying and supporting its outward form and properties’; hence it is equivalent to the Latin substantia, Eng. essence and Greek οὐσία . Cf. below III. 7. Later it was applied to the ‘special or characteristic nature of a thing,’ and so became the very opposite of οὐσία (the general nature); hence equivalent to person.