The Lutheran scholar, George A. Lindbeck, at the time the professor of theology and director of Graduate Studies, Department of Religious Studies, Yale University, wrote the following about the debate within Catholicism itself, as well as between Catholics and non-Catholics, about Protestant and Catholic concepts of infallibility and the immutability of doctrine:
Protestants and Catholics have historically tried to handle this infallibility of the mutable, or mutability of the infallible, in different ways. Protestants have tried to solve the problem by denying the infallibility of post-biblical developments, while Catholics have minimized their mutability, but it would seem that neither can be surrendered without doing violence to the logic of faith. The unchangeable faith must be proclaimed afresh in changing circumstances. God spoke his final Word in Jesus Christ, but he still speaks new words which are authoritative and binding. Even Protestants recognize this in practice, though their theology generally lacks the concepts to do justice to it. The Reformers accepted the non-scriptural language of the ancient creeds. They formulated confessions of their own which we now see made as new affirmations not found explicitly in the Bible to a considerably greater degree than they realized. In recent times, the Barmen Declaration against the German Christians who compromised with the Nazis has dogmatic force for many Protestants, while the condemnation of slavery and even of segregation, even though these are not found in the Bible, are treated in practice as infallible dogmas—and rightly so!—by man people who abhor the very sound of the words.
Just as Protestants have failed to find categories for adequately conceptualizing the binding, guaranteed or infallible element in dogma, so Catholics have not succeeded in doing justice to its mutability. Up until one hundred fifty years ago, everyone, Catholics and Protestants alike, thought basically in terms of immutability; and this involved both groups in impossible intellectual gymnastics. Catholics postulated two-source theories of revelation according to which all doctrine not found explicitly in the Bible had been handed down orally from generation to generation, while Protestants either argued that their doctrines were simply the reproduction in brief form of what a purportedly infallible Bible says, or else tried to ignore two thousand years of history, of tradition, and held, in the famous phrase, that “the Bible and the Bible alone is the religion of Protestants”.
The accumulating weight of historical evidence, however, has gradually made the old notions of immutability untenable. Protestants learned to think of the Bible as an historical book and, beginning especially with Newman, Catholics have come to view dogma as historical, as developing. This broke the old connection between immutability and infallibility. Infallibility was seen as a property which a truth need not always have, but which could be gained in the course of time. This, however, was only a partial concession to mutability, for according to the standard theories of development, once a doctrine has acquired infallibility, it can never again lose it. The process is irreversible. Truths of faith may not be permanently infallible in the sense of always having been explicitly known, affirmed and guaranteed since the earliest days of the Church, but once they are guaranteed, their infallibility is irrevocable. (George A. Lindbeck in The Infallibility Debate, ed. John J, Kirvan [New York: Paulist Press, 1971], 124-25, emphasis added)