You can verify that not only in the teachings of “ ‘well-respected’ 19th/20th century theologians,” but in teachings of the magisterium itself.
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There's not a single Catholic source who can be used to support Stubborn's view, but even more than that, literally
any Catholic source will affirm what the "well-respected 19th/20th century theologians" say. Even in the early Church, like the Vincentian canon.
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The universal consensus of the theologians is a sure sign of what the Church teaches. Here's what happens if they can err in consensus:
1) all the priests are
required to be taught according to these manuals. The Church mandates it.
2) all the manuals teach x related to faith or morals (which, according to Stubborn, is plainly wrong)
3) all the priests believe x
wrongly4) all bishops are drawn from all priests, so eventually all
bishops believe wrongly
5) eventually,
everyone believes wrongly
6) The faith is lost universally
One might say that someone can believe rightly
despite the errors of the manuals. And this is called, simply, Protestantism. That
despite what legitimate authority universally teaches, we can still keep the faith! The Church isn't just useless according to this view, it's the single greatest
obstacle to Christian learning that exists!