Fourth Lateran Council – 1215
I. Confession of Faith
We firmly believe and simply confess that there is only one true God, eternal and immeasurable, almighty, unchangeable, incomprehensible and ineffable, Father, Son and Holy Spirit, three persons but one absolutely simple essence, substance or nature. The Father is from none, the Son from the Father alone, and the Holy Spirit from both equally, eternally without beginning or end; the Father generating, the Son being born, and the Holy Spirit proceeding; consubstantial and coequal, co-omnipotent and coeternal; one principle of all things, creator of all things invisible and visible, spiritual and corporeal; who by his almighty power at the beginning of time created from nothing both spiritual and corporeal creatures, that is to say angelic and earthly, and then created human beings composed as it were of both spirit and body in common. The devil and other demons were created by God naturally good, but they became evil by their own doing. Man, however, sinned at the prompting of the devil.
Second Council of Lyon – 1274
I. On the supreme Trinity and the catholic faith
1. We profess faithfully and devotedly that the Holy Spirit proceeds eternally from the Father and the Son, not as from two principles, but as from one principle; not by two spirations, but by one single spiration. This the holy Roman church, mother and mistress of all the faithful, has till now professed, preached and taught; this she firmly holds, preaches, professes and teaches; this is the unchangeable and true belief of the orthodox fathers and doctors, Latin and Greek alike. But because some, on account of ignorance of the said indisputable truth, have fallen into various errors, we, wishing to close the way to such errors, with the approval of the sacred council, condemn and reprove all who presume to deny that the Holy Spirit proceeds eternally from the Father and the Son, or rashly to assert that the Holy Spirit proceeds from the Father and the Son as from two principles and not as from one.