And how do we know that he spoke ex-cathedra?
Hi, friend.
Note well: Everything added by me in this thread is my opinion. Even quotations and cites are my opinion, because my use of the third party material may not be correct.
That being said…
This business about only having to listen to the Pope if he says, “THIS IS AN EX-CATHERDA STATEMENT” is not valid.
For example, if the words “EX CATHEDRA” or “DE FIDE” do not appear in Humanae Vita, are Catholics free to use birth control?
Interestingly, as far as I know the words “ex cathedra” DO appear in Munificentissimus Deus, and Paragraph 20 talks about Mary’s “dead body” not suffering corruption, or rotting, before assumption – and yet many Catholics here – and an article by a website theologian in the website – say that Catholics are free to ignore those words!
Probably, the rule is something like this: One has a duty, as a Catholic ascribing to the validity of “Church,” to abide by the Church’s rulings on faith and morals (not history, not science, although there are crossover points comprising exceptions to those exclusions) unless one can cite, within oneself, an articulable logically compelling and morally compelling reason for disagreeing.
For example, suppose a validly-elected pope gets angry at the cardinals over a disagreement over the definition of infallibility, and perversely publishes an encyclical reading, “I declare, ex cathedra, that all ex cathedra statements are invalid.”
(In theology class at St. Joe’s University, we used to talk about things like, “Well, wouldn’t God do something like strike a perverse pope dead before letting him issue such an encyclical?”)
There would be a duty to think, “Hmmm, that Encyclical is NONSENSE, and must be disobeyed!”
Liberius’ destroyed statement would functionally be such a perverse encyclical. Note that God did not strike him dead to stop its issuance.
Athanasius was able to cite within himself are articulable logically and morally compelling reason for disagreeing. So, he flaunted the Church’s teaching, and then the Pope himself flaunted the Church’s teaching with a new teaching.