Book IV. This book is in a sense the beginning of the treatise, and is sometimes cited later on as the first. Its three predecessors, he says in § 1, had been written some time before. They had contained a statement of the truth concerning the Divinity of Christ, and a summary refutation of the various heresies. He now commences his main attack upon Arianism. First (§ 2) he repeats what his difficulty is; that human language and thought cannot cope with the Infinite. Then (§ 3) he tells how the Arians explain away the eternal Sonship of Christ. As a defence against this tampering with the truth, the Church has adopted the term Homoousion (§§ 4–7); Hilary explains and defends its use. In § 8 he shews, by a collection of the passages of Scripture which they wrest to their own purposes, that such a definition is necessary, and in §§ 9, 10 that their use of these passages is dishonest. In § 11 he tells us exactly what the Arian teaching is, and sets it forth in one of their own formularies, the Epistola Arii ad Alexandrum (§§ 12, 13). In § 14 this doctrine is denounced; it does not explain, but explains away. The proclamation made through Moses, Hear, O Israel, the Lord thy God is One, upon which the Arians take their stand, reveals only one aspect of the truth (§ 15). It does not exhaust the truth; for God is represented as not one solitary Person in the history of creation (§§ 16–22), in the life of Abraham (§§ 23–31), and in that of Moses (§§ 32–34). And this again is the teaching of the Prophets, as is shewn by passages selected from Isaiah, Hosea, and Jeremiah (§§ 35–42). All the evidence thus collected shews that in the Godhead there is both Father and Son, and that the Son is God.