It belongs to the first treatise of Dogmatic Theology (De Deo Uno) to show that God is one and personal. The pantheistic fiction of an impersonal God is sufficiently exploded by the Almighty’s own solemn declaration (Gen. 3:14): “I am Who am.”1

Whether the infinite personality of God must be conceived as simple or multiplex, is a matter which human reason cannot determine unaided. On the strength of the inductive axiom, “Quot sunt naturae, tot sunt personae,” we should rather be tempted to attribute but one personality to the one Divine Nature. Positive Revelation tells us, however, that there are in God three really distinct persons: Father, Son, and Holy Ghost. This fundamental dogma, which essentially differentiates the Christian conception of God from that of the Pagans, the Jews, and the Mohammedans, is designated in the technical Latin of the Church as “Trinitas,” a term first used, so far as we know, by Theophilus of Antioch2 and Tertullian,3 and which later became current in ecclesiastical usage and was embodied in the Creeds.4 In the private symbolum of St. Gregory Thaumaturgus mention is made of a “perfect Triad” (τριὰς τελεία). Didymus the Blind, Cyril of Alexandria, Hilary, Ambrose, and Augustine have written separate treatises “On the Trinity.”

1 Cfr. Pohle-Preuss: God: His Knowability, Essence, and Attributes, 2nd ed., St. Louis, 1914.

2 Ad Autolyc., II, 15: “Τριάδος τοῦ θεοῦ καὶ λόγου καὶ τῆς σοφίας αὐτοῦ” (On the three books Ad Autolycum, see Bardenhewer-Shahan, Patrology, pp. 66 sq., Freiburg and St. Louis 1908. On the word τριάς, cfr. Newman, Athanasius, II, 473 sq., 9th ed., London 1903.)

3 De Pudicitia, c. 21: “Trinitas unius divinitatis, Pater et Filius et Spiritus Sanctus.”

4 Denzinger-Bannwart, Enchiridion Symbolorum, ed. 10, nn. 213, 232, Friburgi Brisgoviae 1908.