The point of his question is that the Pope’s infallibility is also limited within the scope of faith and morals. In other words, he is not able to define anything thing related to faith and morals, but on those doctrines contained within the deposit of faith handed down by the apostles.
But what they are they ? The d. o. f. is a null set, which is filled up by the Popes, each of whom is equipped to fill it up as he sees fit. This means there are in principle as many deposits as Popes.
The Pope cannot make up a new doctrine and define it.
His question is: Would it be possible for a Pope to make up a new doctrine and then attempt to define it as a dogma.
I’m not sure if the charism of infallibility would prevent such an error from occurring, but it might.
The definition of Papal Infallibility, as it was defined at Vatican I reads:
In the same section of the Council it also says the following:
Vatican I: “For the Holy Ghost was not promised to the successors of Peter that by His revelation they might disclose new doctrine, but that by His help they might guard sacredly the revelation transmitted through the apostles and the deposit of faith, and might faithfully set it forth.”
From this we know that the Holy Ghost was not promised to the Pope so that he could make new doctrines, but only that he could infallibly define doctrines contained in the deposit of faith.
I am not sure what the answer is.
The problem with words, is that they mean what one wants them to mean or needs them to mean . So “new doctrine” is as new as the Pope and his theological advisers say it is - the proposed dogmatisation of the co-redemption is a good example of this.
What, after all,* is* “a new doctrine” ?
One not explicitly taught ?
One of which the parts are not explicitly taught, or not all of them ?
One not logically implied by one that has been taught ?
All of which raises the question, “Is Papal infallibility anything more than a form of secularism ?” IMO, it is indeed that; & it may be significant that it has so much in common with Protestant Fundamentalism: both want guarantees of the truth of what they believe, both are rationalist, both in effect deny that Christians who prefer faith to Fundamentalist rationalism are “real Christians”, neither is capable of thinking that Christianity might just be able to be different from their own notions of it.
Assenting to Papal infallibility is in practice more important than that the dogma should have a stable content - and this too happens in Protestant Fundamentalism: it is more important for them to admit that the Bible is totally inerrant, than for their belief to be understood in the same way; which makes it an empty doctrine. Papal infallibility is equally content-free; for the very good reason that it cannot escape historical details - and these in turn are always open to re-interpretation. As a result, the dogma is infinitely malleable, it is a “nose of wax”. So it can mean anything at all. So it is useless as a protection against error. And it destroys the perpetuity of the faith at a stroke - it is simply untrue that the Apostles believed in the Assumption; for if they did, there is is no evidence of it at all. And what is not known to be a fact, cannot be asserted to be a true fact; not even if the Pope asserts it. He is not Lord of the Truth - but the servant of it.
Unless he has means of knowing such things that others lack - if he has, historians of dogma would doubtless be very eager to know what these sources are. But if he is free to define as a fact what is not known to be a fact, it is hard to see why historians cannot appeal to apparitions of long-dead characters as sources of historical information.
Which means that there is nothing to stop a pope after 1870 deciding that he can define something that Pius IX and his precedessors would not have regarded themselves as having the competence to define (which curiously enough is also what happened in the history of the Immaculate Conception).
Maybe there are answers to all these objections to the dogma. IMHO, the definition of Papal Infallibility was a great mistake; but as the Church rests upon the grace of Christ, and not upon any human righteousness (such as that of never being wrong in doctrine), and as He is Faithful even though we are not, I don’t think it matters. ##