Let us examine, then, by the evidence of facts, whether the Church of Rome believes her own claim to infallibility. Acting is the test of belief. If a quack claimed to have a universal medicine, warranted to cure all diseases, we should not need to inquire into the proofs of its virtues if we saw his own children languishing in sickness, and found that he never tried his medicine on them. If an alchemist asserted that he possessed the philosopher’s stone, and could turn the baser metals into gold, his pretensions would be disposed of if we saw his own family starving, and that he made no attempt to make any gold to relieve them.
The simple answer, then, to the question, why we do not use traditions as well as Scripture in the proof of Christian doctrine, is that we do not know of any trustworthy enough and what we have seen of the failure of tradition proves to us that there were good reasons why God should have granted us in Scripture a more secure channel for conveying Christian truth. But if it is alleged that it can be established by uninspired testimony that any doctrine not contained in Scripture is part of the Christian scheme, let the evidence be produced, and we are willing to consider it.
The Infallibility Of The Church. Chapter 2: The Cardinal Importance of the Question of Infallibility
You must carefully observe that the Doctrine of Development would be fatal to the Roman Catholic cause if separated from the doctrine of the Infallibility of the Church. Without the latter doctrine the former, as I have already pointed out, leads to Protestantism or to infidelity rather than Romanism. In fact, the motto of the doctrine of Development is ‘We are much wiser men than our fathers.’
George Salmon • 19th Century • From The Infallibility of the Church • Council of Trent, Doctrine of Development, Doctrine of Infallibility, Henry Edward Manning, John Henry Newman, Old Catholics, Oxford Movement, Rule of Faith, Vatican Council