Constitution De summa Trinitate et fide catholica (1274), Denzinger no. 460

With faithful and devout profession we confess 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 a single spiration. This the most holy Roman Church, mother and teacher of all the faithful, has professed, preached and taught until now; this she firmly holds, preaches, professes and teaches. This is the unchangeable and true judgement of the orthodox Fathers and Doctors, Latin and Greek alike. But because some, through ignorance of the aforesaid irrefutable truth, have fallen into various errors, we, desiring to bar the way to errors of this kind, with the approval of the sacred Council condemn and reprove those who shall presume to deny that the Holy Spirit proceeds eternally from the Father and the Son, or who with rash daring shall assert that the Holy Spirit proceeds from the Father and the Son as from two principles and not as from one.