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Me: Ah, so the Summa Theologia IS considered infallible! (Assuming that if the Magisterium and Pope are, then their trusted sources must be through them!)

Catholic: No, it isn't infallible by itself, just as an individual bishop isn't infallible by himself.

I'm confused. If the Pope and the Magisterium are infallible, why aren't their trusted resources seen as such? Surely, at some point, some Pope or Magisterium must have indicated whether such a famous theological text is or is not of relevance?

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Your Catholic friend is right, btw. – Affable Geek Jan 17 '14 at 17:08
Just a note: Magisterium is an abstract noun, meaning the whole of the teaching authority of the Church. It's continuous, the Magisterium: there are not more than one. (You can't have "some Magisterium or other") – Andrew Leach Jan 17 '14 at 17:16
Related: What's wrong with the Summa Theologica? has an answer that shows a difference of opinion on the Immaculate Conception between Aquinas (saying Mary was conceived in sin, ST 3.31.8 ad 2) and Pius IX's Ineffabilis Deus, held to be infallible. – James T Jan 17 '14 at 17:33
@AffableGeek are some 'bits' infallible? I mean, his description of beatific vision seems widely accepted. And SOME Pope at SOME stage must have discussed it... – Sehnsucht Jan 17 '14 at 18:36
Suggesting that the magisterium ordinarium (the "ordinary teaching office of the Church") is infallible does not mean that any specific texts are infallible, merely that the tradition as a whole is. – lonesomeday Jan 17 '14 at 19:33

3 Answers 3

I'm not a Catholic, so I'm relying on secondary sources here, but my understanding --as confirmed by --is that the Pope is not considered infallible at all times, but only when he issues a statement ex cathedra, which is to say, that is intended to be taken as an infallible, definitive statement of the church as guided by God.

This related article seems to indicate that the church's endorsed theological documents are also be a mixture of beliefs considered as as fallible and as infallible.

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The Summa Theologica (and all other documents of this nature) are not considered infallible. The reason for supposing they are indicates a misunderstanding of the Catholic concept of the Magisterium of the church, of how it is exercised, and of its specific degrees (whether "ordinary" or "apostolic").

So the short answer is that the underlying premise that everything the Pope teaches is infallible is simply a flawed premise.

More detail can be found on this answer.

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Vatican I defined Ex Cathedra statements are those which meet the following conditions, The Roman Pontiff speaks on a matter of faith or morals to the Universal Church. St. Thomas Aquinas was never a Pope, so he never could meet these conditions.

Therefore, faithfully adhering to the tradition received from the beginning of the Christian faith, to the glory of God our savior, for the exaltation of the Catholic religion and for the salvation of the Christian people, with the approval of the Sacred Council, we teach and define as a divinely revealed dogma that when the Roman Pontiff speaks EX CATHEDRA, that is, when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he defines a doctrine concerning faith or morals to be held by the whole Church, he possesses, by the divine assistance promised to him in blessed Peter, that infallibility which the divine Redeemer willed his Church to enjoy in defining doctrine concerning faith or morals. Therefore, such definitions of the Roman Pontiff are of themselves, and not by the consent of the Church, irreformable.

So then, should anyone, which God forbid, have the temerity to reject this definition of ours: let him be anathema.

Text from

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