So then in the first sense of the word the three absolutely divine subsistences of the Holy Godhead agree: for they exist as one in essence and uncreate. But with the second signification it is quite otherwise. For the Father alone is ingenerate, no other subsistence having given Him being. And the Son alone is generate, for He was begotten of the Father’s essence without beginning and without time. And only the Holy Spirit proceeds from the Father’s essence, not having been generated but simply proceeding. For this is the doctrine of Holy Scripture. But the nature of the generation and the procession is quite beyond comprehension. — Book I, Chapter 8, Concerning the Holy Trinity.