55. Let us take them, then, in their order. In the Old Testament—to cite one out of a multitude of testimonies—it is written: “Before Me hath there been no other God, and after Me shall there be none.” Is. xliii. 10. I will not comment on this place, but ask thee straight: “Who speaks these words,—the Father or the Son?” Whichever of the two thou sayest, thou wilt find thyself convinced, or, if a believer, instructed. Who, then, speaks these words, the Father or the Son? If it is the Son, He says, “Before Me hath there been no other God;” if the Father, He says, “After Me shall there be none.” The One hath none before Him, the Other none that comes after; as the Father is known in the Son, so also is the Son known in the Father, for whensoever you speak of the Father, you speak also by implication of His Son, seeing that none is his own father; and when you name the Son, you do also acknowledge His Father, inasmuch as none can be his own son. And so neither can the Son exist without the Father, nor the Father without the Son. This holds good also of human fatherhood and sonship. The terms of a relation involve each the existence of the other—no father, no son, and equally, no son, no father. The Father, therefore, is eternal, and the Son also eternal.