Eunomius, whom Ullmann calls one of the most interesting heretics of the Fourth Century, was by birth a Cappadocian, and slightly older than Gregory.  As a young man he was a pupil and amanuensis of Aëtius, by whom the Arian heresy was developed to its extreme results.  The disciple never shrank from drawing the furthest logical conclusions from his master’s premises, or from stating them with a frankness, which to those who regarded the premises themselves from which he reasoned as horrible blasphemies, seemed nothing less than diabolical in its impiety.  So precisely did he complete and formulate his teacher’s heretical tenets, that the Anomœan Arians were ever afterwards called Eunomians, rather than Aëtians.  They asserted the absolute Unlikeness of the Being of the Father and of the Son.  Starting with the conception of God as Absolute Being, of Whom no Generation can be predicated, Unbegotten and incapable of Begetting, they went on to say that an Eternal Generation is inconceivable, and that the Generation of the Son of God must have had a beginning.  Of course, therefore, the Arian conclusion followed, namely, that there was a time when the Son did not exist (ἦν ποτὲ ὅτε οῦκ ἦν), and His Essence is altogether unlike that of the Unbegotten Father.  Equality of essence and Similarity of essence, are alike untenable, from the mere fact that the one Essence is Unbegotten, and the other is Begotten.  The Son, they said, is the First Creation of the Divine Energy, and is the Instrument by whom God created the world, and in this sense, as the Organ of creative power, may be said to be the Express Image and Likeness of the Energy of the Father. Two terms borrowed from Holy Scripture (Heb. i. 3).  But observe, borrowed with a difference—not “the Image of His Substance,” which they would not admit, but of His “Energy,” which is a very different conception.