_definitely interpreted_; for it was only by the aid of a definite interpretation that the creed could be used to repel the Gnostic speculations and the Marcionite conception of Christianity. In this state of matters the Church of Rome, the proceedings of which are known to us through Irenaeus and Tertullian, took, with regard to the fixed Roman baptismal confession ascribed to the Apostles, the following step: The Antignostic interpretation required by the necessities of the times was proclaimed as its self-evident content; the confession, thus explained, was designated as the "Catholic faith" ("fides catholica"), that is the rule of truth for the faith; and its acceptance was made the test of adherence to the Roman Church as well as to the general confederation of Christendom. Irenaeus was not the author of this proceeding. How far Rome acted with the cooeperation or under the influence of the Church of Asia Minor is a matter that is still obscure,[34] and will probably never be determined with certainty. What the Roman community accomplished practically was theoretically established by Irenaeus[35] and Tertullian. The former proclaimed the baptismal confession, definitely interpreted and expressed in an Antignostic form, to be the apostolic rule of truth (regula veritatis), and tried to prove it so. He based his demonstration on the theory that this series of doctrines embodied the faith of the churches founded by the Apostles, and that these communities had always preserved the apostolic teaching unchanged (see under C). Viewed historically, this thesis, which preserved Christianity from complete dissolution, is based on two unproved assumptions and on a confusion of ideas. It is not demonstrated that any creed emanated from the Apostles, nor that the Churches they founded always preserved their teaching in its original form; the creed itself, moreover, is confused with its interpretation. Finally, the existence of a _fides catholica_, in the strict sense of the word, cannot be justly inferred from the essential agreement found in the doctrine of a series of communities.[36] But, on the other hand, the course taken by Irenaeus was the only one capable of saving what yet remained of primitive Christianity, and that is its historical justification. A _fides apostolica_ had to be set up and declared identical with the already existing _fides catholica_. It had to be made the standard for judging all particular doctrinal opinions, that it might be determined whether they were admissible or not.