I was invited to a group called "Five solas vs Catholic Church". I am a Catholic and thus against the collection five solas though not all of them equally. Here is the first one.
It is in a certain manner opposite to both Tradition as Infallible and Magisterium as Infallible.
It is therefore erroneous.
It is actually more opposed to Tradition as Infallible than to Magisterium.
The opposite of Magisterium as infallible and as compulsory is not so much Sola Scriptura as such as the Private Judgement on the Sola Scriptura.
The total and erroneous Protestant doctrine is therefore bipartite:
Error 1: Apostolic Christianity is generally accessible through Bible alone as opposed to Bible and Tradition.
Error 2: Individually we are responsible to the Sola Scriptura only through direct Private Judgement on its content. A man who is unlearned and leaves a point out from his individual Bible reading understanding is not excused for chosing as probable a wrong solution because he was feeling he had to submit to a Magisterium that was wrong, but he was instead in such a case wrong to take Magisterium as above himself in the manner God is and Bible are. Infallibility belongs only to God, is the claim, not to either man individually or any group of men together.
That the second is untrue is clear from the Bible. It says "The Church is the Pillar and Foundation of Truth". Christ is its head and as God and as sinless man infallible, which even Protestants admit, but if Christ alone in the Church were infallible on any point, then there would be a neck problem, the body not communicating properly with its head. So, we must say that the visible Church today - whereever it truly is - is infallible when speaking unitedly.
That the first is untrue is also clear from the Bible as well as from the Church.
One bit of a warning, to things like Modernist Catholics. Or semimodernist who think they must "obey" modern magisterium in accepting modern cosmology or deep space or deep time with evolution.
A Protestant would not agree that private judgement is an excuse for disagreeing with the Bible. A Catholic must therefore not agree that Magisterium (above his private judgement, when genuine and when his private judgement as bishop or Pope is not preceding the magisterial one on hitherto undecided questions), he must as said not agree that Magisterium is any kind of excuse for disagreeing either with Bible (72 books*, not just 66) or with Tradition.
Furthermore, on those particular matters, there seems to be no consensus about what is magisterium and, supposing CCC is such, whether CCC is sufficiently obliging. But insofar as Catechism of the Catholic Church endorses as "knowledge" things that contradict Bible or Tradition (specifically theories contradicting a young and "small" universe), it would be like a Protestant who in private judgement thought "this is my Body" or "whatever you bind on earth" as something the Bible did not clearly indicate what to believe about. Such a Protestant is no longer a Christian, and if any bishop or Pope puts full weight into certain modern theories included in certain paragraphs thereof, such a Magisterium is no longer Christian and therefore no longer magisterial either.
BpI Georges Pompidou
Sunday after Sts Peter and Paul
72 if, as traditionally, the canonical book of Baruch is not counted as a separate book but as an appendix to Jeremiah (whose secretary Baruch was). Otherwise it is 73.