If the Church erred in giving to the faithful an evil or defective liturgical rite, (for example in promulgating the Novus Ordo) this can only mean that She has failed in her duty to safeguard divine worship. This can only mean that the Church has defected, which is impossible.

If Paul VI was indeed Pope, then the NOM is not defective, but equally pleasing to God. Just as all the other liturgical rites existing in the Church today, all approved by the Holy See, all equally pleasing to God. The ONLY way the NOM is invalid, evil, inferior, etc., is if Paul VI was not Pope.

Cantarella, I started this post because someone had questions about what Quo Primum said.  Please do not derail this thread with sede arguments.  It's a great topic you bring up, but should be a separate thread.  Thank you.

Cantarella, I started this post because someone had questions about what Quo Primum said.  Please do not derail this thread with sede arguments.  It's a great topic you bring up, but should be a separate thread.  Thank you.

OK, I'm sorry.

As far as the OP, I think there is something important that was not addressed:

In 2c. when the Pope says:

" Only this new rite is to be used, unless in the same Churches from their first institution more than two hundred years ago and confirmation by the Apostolic See"

He is explicitly stating his Tridentine Mass is a NEW liturgical rite.

Also, when he says:

"that priests may know which prayers to use, and which rites and ceremonies they were required to observe in the celebration of Masses."

St. Pius V makes it clear that he is dealing with the Missal itself (not the doctrine or theology of the Mass). This is another proof that Quo Primum is discipline and thus, modifiable by another equally powerful Pope. A bull which deals with the prayers, ceremonies and rites used by the Church belongs to the realm of discipline, not dogma.

He is explicitly stating his Tridentine Mass is a NEW liturgical rite.

Stubborn is correct.  It's a new missal, in the sense that it organized the rubrics in a new way.  It's not new in the sense that what it contains, doctrinally and liturgically, is new.  95% of what was in the Quo Primum missal was in all the other hundreds of rites which it outlawed.  Quo Primum just cleaned up the 5% of rubrics which were added to each Order and diocese over the centuries, and were added out of respect and love of the mass.  But such additions had become too varied and needed uniformity.

For example, the Benedictine Order adds "St Benedict" to the Confiteor prayer and his name is added later in the mass.  But since this rite is older than 200 years, they are allowed to keep these rubrics.  The other Orders at the time also added these type of non-essential elements to the prayers of the Mass, which QP put a stop to.

Contrast the meaning of the word "new" to the novus ordo, which was both a new rite, in essentials and non-essentials, and a new theology.

A bull which deals with the prayers, ceremonies and rites used by the Church belongs to the realm of discipline, not dogma.

Wrong.  The prayers, ceremonies and rites of the Church are both of Divine and human origin.  Therefore these rites have to do with doctrine (i.e. Divine elements) and discipline (human elements).