At his engaging blog Mutual Enrichment, Fr John Hunwicke has a good note about Pius V and Quo primum. He points out a common error or two about that famous Apostolic Constitution.
Quo primum was the instrument of promulgation of the first “Tridentine” missal, the 1570 Missale Romanum, which – with alterations – is in use today in the form of the 1962 edition (the Extraordinary Form).
Fr. H says (in part):
There is a myth which is endlessly repeated … I groan every time I read it … about the liturgical reforms of S Pius V. It goes like this:
(1) He wished to standardise and centralise. So he ordered everybody to use his new edition of the Roman Missal (but he did permit those with rites more than 200 years old to keep them).
This is pretty well the opposite of what his legislation ordered. He:
(2) Ordered those with such old rites to keep them. But, if they positively wanted to adopt his new edition instead, he permitted them to adopt it AS LONG AS THE BISHOP AND THE UNANIMOUS CHAPTER WERE IN AGREEMENT.
If you don’t want to believe me, I suggest you read the actual TEXT of Quo primum yourself and find out. DO NOT READ SOMEBODY’S SUMMARY OF THE BULL, BECAUSE THAT WILL (almost certainly) JUST TELL YOU THE MYTH.
Fr. H has more on Pius V HERE
In 2009, I did a PODCAzT about Quo primum which included a reading of the whole document. HERE
BTW… Pius V did not intend with Quo primum to make the 1570 Missale Romanum the Latin Church’s missal “forever”. Often claimed. Wrong.