On April 29,1875...
Venerable John Henry Newman, C.O., wrote to a friend, who was being questioned by someone about the then-recent definition of papal infallibility:

As to your first question, I should say that the word "infallibility" has never been ascribed to the Church in any authoritative document till the Vatican Council—and it has been not unfrequently urged as an objection (and I think by myself in print in former days) that the Church's "infallibility" was not de fide. Yet the Church acted as infallible and was accepted as infallible from the first. What was the case with the Church was the case with the Pope. The most real expression of the doctrine is, not that he is infallible but that his decisions are "irreformabilia" and true. So that the question did not arise in the mind of Christians in any formal shape "is he infallible, and in what and how far?" for all they felt was that what he said was "the voice of the Church," "for he spoke for the Church," "the Church spoke in him," and what the Church spoke was true. And accordingly his word was (to use a common phrase) "taken for gospel," and he meant it "for gospel," he "laid down the law," and he meant to "lay down the law"—he was sure he was right, no one had any doubt he was right—he was "the proper person to speak and to settle the matter." This (with whatever accidental exceptions) was his and the Christian world's feeling in the matter—as any ordinary man now, (bigoted Protestant, if you will, acting from prejudice) says "I know I am right," so the Pope would say "I know it is so, and it is my duty to tell the flock of Christ so," without analyzing whether it was a moral certainty, or an inspiration or a formal limited infallibility, or whatever other means which was the ground of his unquestioning and his absolute peremptoriness. Honorius then or any other Pope of those times, when he chose, acted as infallible and was obeyed as infallible, without having a clear perception that his ipse dixit arose from a gift of infallibility.

But again, at least the Church acted as infallible from the first, e.g. in Councils, &c.—Now the Pope ever acted in company with the Church, sometimes before the hierarchy, sometimes after, sometimes simultaneously with, the hierarchy. He always spoke as the voice of the Church. The Vatican Council has decided that he is not only the instrumental and ministerial head or organ of the Church, not only has a power of veto, not only is a co-operating agent in de fide decisions, but that in him lies the root of the matter, that his decision, viewed separate even from the Bishops, is gospel.

Before the Vatican Council, even Gallicans allowed that the Pope was infallible, supposing the Bishops accepted his decision—and at least that Honorius would feel, supposing him led to make any ex cathedra decision, so that I deny your correspondent's words, "he could not in the 7th Century actually intend to exert that infallible authority, which has been dogmatically defined in the 19th." Yes, he could, and though he might not be clear as to the conditions of infallibility, though he might take for granted, or implicitly expect, and be sure of, the concurrence of the Bishops of the world with him as a condition of the act being infallible.

The account I have given of the Council of Ephesus in "Theodoret" in Historical Sketches is a further illustration of what I have tried to bring out here.

I might have taken a higher ground, for long before the Vatican Council, though not perhaps in the time of Honorius, Popes have realized to themselves their own infallibility, and from the first, as we see in the history of St. Victor, St. Stephen, St. Dionysius in the Ante-nicene times—they have acted as if their word was law, without making nice distinctions.

When your correspondent says "Previous to the Vatican Council no doctrines defined only by the Pope are absolutely to be received," I remark on the contrary there was such an agreement in fact between Pope and Bishops that, when he taught and was followed by the world, (as took place) it was impossible to discuss whether the Bishops concurred by an act of independent judgment or by an act of submission to him. Practically the Pope has taught dogmatically from the first, e.g. it is not at all clear that Leo's famous Tome against Eutyches is an act of infallibility; but what is clear is that it had the effect of turning a great mass of Bishops right round, as if he were infallible, and making them with him in the Council of Chalcedon use the words definitive of the two natures in One Person, which he had in his Tome forced upon them. He has been from the first (where history is minute enough for the purpose) the beginning and the end, he has had the first and last word, of every definition. You understand me, I am bringing out my view, without stopping to notice objections or opposite statements.

Well, and now I am not sure whether I have expressed myself clearly, and should like you to tell me, whether it enables you to answer your correspondent.

But any how I am tired just now, and shall reserve your second question for another letter.

When you write, tell me honestly that you are well, for till you are quite, I think you must honestly watch over your doings.