July 14th, 1570

Today is the 450th anniversary of the Apostolic Constitution Quo primum by which Pope Saint Pius V promulgated the revised Missale Romanum mandated by the Council of Trent.

The core of the document is the oft-quoted (and misquoted) third and fourth paragraphs.

Let all everywhere adopt and observe what has been handed down by the Holy Roman Church, the Mother and Teacher of the other churches, and let Masses not be sung or read according to any other formula than that of this Missal published by Us. This ordinance applies henceforth, now, and forever, throughout all the provinces of the Christian world, to all patriarchs, cathedral churches, collegiate and parish churches, be they secular or religious, both of men and of women – even of military orders – and of churches or chapels without a specific congregation in which conventual Masses are sung aloud in choir or read privately in accord with the rites and customs of the Roman Church. This Missal is to be used by all churches, even by those which in their authorization are made exempt, whether by Apostolic indult, custom, or privilege, or even if by oath or official confirmation of the Holy See, or have their rights and faculties guaranteed to them by any other manner whatsoever.

This new rite alone is to be used unless approval of the practice of saying Mass differently was given at the very time of the institution and confirmation of the church by Apostolic See at least 200 years ago, or unless there has prevailed a custom of a similar kind which has been continuously followed for a period of not less than 200 years, in which most cases We in no wise rescind their above-mentioned prerogative or custom. However, if this Missal, which we have seen fit to publish, be more agreeable to these latter, We grant them permission to celebrate Mass according to its rite, provided they have the consent of their bishop or prelate or of their whole Chapter, everything else to the contrary notwithstanding.

These have often been used by folks to argue that the Missal of 1570 is fixed forever without change. And yet, in 1604  Pope Clement VIII replaced it with a new typical edition. Many, many revisions followed, culminating in the wholesale revision of the rites in 1970, which has itself been revised in two new typical editions since then, as well as several small changes to the calendar.

What the supreme legislator legislates, he can re-legislate.