The Doctrinal Note of the Dogma of Subsistent Relations

(Clue: the answer is in the title)

De Fide Divina et Catholica Definita

"First, then, the holy Roman church, founded on the words of our Lord and Saviour, firmly believes, professes and preaches one true God, almighty, immutable and eternal, Father, Son and holy Spirit; one in essence, three in persons; unbegotten Father, Son begotten from the Father, holy Spirit proceeding from the Father and the Son; the Father is not the Son or the holy Spirit, the Son is not the Father or the holy Spirit, the holy Spirit is not the Father or the Son; the Father is only the Father, the Son is only the Son, the holy Spirit is only the holy Spirit. The Father alone from his substance begot the Son; the Son alone is begotten of the Father alone; the holy Spirit alone proceeds at once from the Father and the Son. These three persons are one God not three gods, because there is one substance of the three, one essence, one nature, one Godhead, one immensity, one eternity, and everything is one where the difference of a relation does not prevent this. Because of this unity the Father is whole in the Son, whole in the holy Spirit; the Son is whole in the Father, whole in the holy Spirit; the holy Spirit is whole in the Father, whole in the Son. No one of them precedes another in eternity or excels in greatness or surpasses in power. " D703

17th ECUMENICAL COUNCIL (FLORENCE 1438-1445)