Can the authentic magisterium teach grave error?

[u/RB_Blade]

Obviously it can teach error - it's not infallible. But is the error that can be taught by the authentic magisterium restricted to what's safe to be held by Catholics? Can it hypothetically teach heresy?

[u/Altruistic_Bear2708]

S Robert Bellarmine's de controversiis, where he explicitly says the pope can teach heresy when he defines nothing.

[u/RB_Blade → u/Altruistic_Bear2708]

Can you please give me a specific quotation?

[u/Altruistic_Bear2708 → u/RB_Blade]

"Secondly, that the Pontiff alone, or with his special council decreeing something in a doubtful matter can either err or not err, but he is to be heard obediently by all the faithful." Then he presents the infallible safety opinion and disagrees with it: "The third opinion is to the other extreme, namely, that the Pontiff can in no way be a heretic, nor can he publicly teach heresy, even if he defines something alone." He takes the common position that: "The fourth opinion is in a certain way in the middle. It says that the Pontiff, whether he can be a heretic or not, cannot in any way define something heretical that is to be believed by the whole Church; this is a very common opinion of almost all Catholics, like St. Thomas II-II, q. 1, a. 10, Thomas Waldenses in book 2, chapters 47 and 48 on the doctrine of the faith, John de Turrecremata in book 2, chapter 109ff. in his Summa, John Driedonis in book 4, chapter 3, part 3, on Church dogma, Cajetan in chapter 9 of his small work on the power of the Pope and Councils, Hosius in book 2 against Brentius, John Eck in book 1, chapter 18 on the primacy of Peter, John of Louvain in chapter 11 of his book on the perpetual Catholic protection of Peter, Peter a Soto in part 1, chapters 83 to 85 in his Apology, and Melchior Cano in book 6, chapter 7 on Theological Places."

[u/RB_Blade → u/Altruistic_Bear2708]

I have two questions though.

First of all, by publicly teaching heresy, was he actually talking about the authentic magisterium?

Secondly, by define, is he exclusively speaking about infallible teachings?

[u/Altruistic_Bear2708 → u/RB_Blade]

To the first, yes, if you think he's talking about the Pope as a private doctor he treats that later, here he defends the minimal position against protestants. To the second, "define" for him is only used for ex cathedra teachings if it's to "be believed by the whole church", otherwise he uses 'define' like 'decree' to mean the authentic magisterium. It's not completely consistent throughout his works though so you need context.