Chapter 10 — Part I: The Creed — Article VIII: I Believe in the Holy Ghost
Section 6. No one should be surprised that a proper name is not given to the Third, as to the First and Second Persons. The Second Person is designated by a proper name, and called Son, because, as has been explained in the preceding Articles, His eternal birth from the Father is properly called generation. As, therefore, that birth is expressed by the word generation, so the Person, emanating from that generation, is properly called Son, and the Person, from whom he emanates, Father.