Laszlo Dobszay, in his book The Bugnini-Liturgy and the Reform of theReform, has a detailed discussion of the rupture with tradition that occurred in the liturgy of Pope Paul VI. One important part of this rupture is in the proper chants - Introit, Gradual, Alleluia, Tract, Offertory, and Communion. For those interested, I recommend a close reading of Dobszay's treatment - there is much to be learned.
In the Roman liturgical tradition, the proper chants came into being at a very early stage in the history of the Roman rite. The music and the texts of these chants developed simultaneously, and were basically inseparable from one another. The text was, of course, the most essential element to the rite, but the music was also essential as the medium whereby the text played its liturgical role. (For this reason, the traditional Sung Mass should be considered the normative mass, rather than the Low Mass.) Now, the texts of the chants were for the most part taken from scripture, and were chosen according to the message of the particular liturgical day in which they were to be sung. The choice of texts resulted from centuries of theological and spiritual reflection by the Church Fathers. These chants represented the various spiritual dispositions with which the Roman Church approached the various moments of the liturgical year. They became a genuine and integral part of the liturgy. The chants which were assigned to the different days of the year were fixed in more or less their present arrangement at an early period – probably the 7th century, if not earlier. The core of the arrangement which we find in the current Tridentine missal is thus around 1200 years old. Because this continuity exists throughout the greater history of the liturgy, it is a genuine indication of how the Roman Church approaches her spiritual life by means of the liturgy.
In the Missal of Pope Paul VI, the proper chants are no longer the integral part of the liturgy which they once were, but are reduced to an option. They may now be substituted by virtually any other song, the criteria for which are practically subject to the determination of individuals. The General Instruction of the Roman Missal indicates that “anything else that is appropriate” or “approved by the Conference of Bishops” may be sung instead of the proper chants themselves. In America this was taken even further: approval by the Bishops is no longer necessary, but “any sacred song” whatsoever may be sung. In effect, the propers are now no longer sung or the texts even prayed.
Of importance is that this has done away not only with a precious treasury of Gregorian melodies, but also with the sacred texts themselves to which these melodies were attached. The loss of the arrangement of these texts constitutes a grave break with a venerable tradition that had its roots in the ancient spirituality of the Church Fathers themselves. Thus, an essential part of the traditional Roman rite has been practically destroyed. As Dobszay writes, “he who removes the Proper chants from the Mass of the day or the season (e.g., Advent or Lent), mutilates the liturgy and diminishes the content of the feast, by depriving the praying Church of an excellent means of fully understanding the feast being celebrated… I dare say that whoever removes the proper chants, mutilates and diminishes the theology as well, which lives not only in manuals and textbooks, but also in the spirituality of the praying Church, the Ecclesia orans.” (Bugnini-Liturgy, pgs. 93-94).
I would be interested, perhaps later, in doing a more in depth study of this theological treasury of which Dobszay speaks, in order first to gain a greater appreciation of the Catholic liturgical tradition, and also to learn what we have lost in the recent reforms.