|Salisbury Cathedral, home of the old Sarum Rite|
Before the Council of Trent, there was a considerable degree of variety among the liturgies of the Roman Rite. Particular dioceses, cathedrals, and religious orders each had their own ways of celebrating the Roman liturgy. Those variants could very accurately be called species of the genus which was the Roman Rite. One of these rites was the well known but now defunct rite of Sarum, originally based in the diocese of Salisbury, England. While these variants were each different in many respects, they all shared a huge amount of common material which identified them generically with the liturgy that formed in the city of Rome. This common core which they all shared had undergone a gradual development over the centuries, remaining stable in its main elements for about 1000 years. The stability and age-old continuity is where can be observed the liturgical tradition of the Roman Rite.
The main elements of the old Roman Rite, constituting the common core of the medieval variants, could be listed as the following: The Order of the Mass (in its broad structure, not all of its specific prayers), the immobile Canon of the Mass, the Lectionary, the Orations, the Proper Chants, the Psalter of the Divine Office, parts of the calendar, the rites of Holy Week, and quite a lot more. The medieval variants of the Roman Rite would have varied mostly in the particular prayers and rituals for the Order of Mass, and would very often have additional local feast days with their own sets of Propers. In practically all other respects, however, they coincided remarkably well with each other and with the centuries-old rite of the city of Rome.
Pope St. Pius V, in codifying what we now call the Tridentine rite, really just took one of these variants of the Roman Rite, namely that which was used by members of the Roman Curia at the time, made some adjustments to it, and imposed it almost universally in the Roman Church. The Tridentine Missal is almost identical to the Curial Missal of a century earlier, from the year 1474. But Pius V still permitted many of the other variants to continue to be celebrated, provided that they were over 200 years old. This was to prevent any celebration of a liturgy which might have been influenced by the rife liturgical abuse and the Protestant Reformation which had occurred within that space of time. Thus Pius V's legislation, as far as its liturgical content was concerned, remained remarkably faithful to liturgical tradition. Unfortunately, many of the variants died out in practice, nonetheless, in favor of the usually simpler and shorter Tridentine form. Only a few remained, mainly those connected to religious orders such as the Dominicans.
The Novus Ordo and the Liturgy of the Hours of Pope Paul VI broke away dramatically from the old uniformity and continuity of the Roman Rite. The Pauline reform introduced radical and far-reaching changes in almost all of the above-listed features of the Roman liturgy, save perhaps the Order of the Mass, broadly understood. It is interesting to make the following comparisons: whereas any two of the old variants of the Roman Rite could easily be identified as belonging to the same genus, due to the vast amount of common material and liturgical forms, the current Novus Ordo of Paul VI cannot by any stretch of the imagination be so identified as belonging to that same genus, if it be compared to the Tridentine Rite, or to any of the old variants for that matter. There is such a greater difference between the Tridentine and Pauline rites than there is between the Tridentine and, say, the Dominican or Sarum rite, or any other variant, that it is quite absurd to claim that the Novus Ordo and the Tridentine are the same liturgy. Granted, they are both Catholic, they both have the sacrifice of Calvary, but they simply cannot be classified within the same liturgical rite. Moreover, it is precisely in those elements which, by the time of Trent, had reached an age of about 1000 years of continuity, and by Vatican II, 1500 years, that the Novus Ordo differs from the older Roman Rite. Exactly the same can be said for the Pauline Liturgy of the Hours, in comparison to the older Roman Divine Office. They are different rites.
This calls into some question the assertion made in Summorum Pontificum by Pope Benedict XVI - God bless him - that the Tridentine and Novus Ordo are to be considered two forms of the same rite - one dubbed Extraordinary, the other Ordinary. In past times, such a manner of speaking could be said only insofar as two liturgical forms shared the common heritage of the ancient Roman Rite. But a simple examination of their content reveals that this same heritage is shared little, if at all, between the Tridentine Rite and the Novus Ordo. They are hardly two forms of the same rite, as far as their actual content is concerned.