ANY TIMES I’ve spoken of my admiration for a special version of the Liber Usualis which has English translations. Published in 1957, this rare & sensational book can be downloaded thanks to the generosity of Dr. William Mahrt.
One reason the book isn’t well known is the title: “Mass & Vespers.” Many people only know “Liber Usualis” (which means “useful book”). They get confused whenever they try to explain what’s actually inside the book: Kyriale, Antiphonale, Graduale, Toni Communes, and so on. In fact, there are many different names for the Liber Usualis, like Paroissien Romain, Manuale Missae et Officiorum, Compendium Gradualis et Missalis Romani, and so forth.
However, this 1957 book is not perfect. As you can verify by the graphic on the right, it says:
There is good reason to think that the first part of the Mass originally contained not two readings only, but three: the first from the Old Testament, the second from the Epistles, the third from the Gospels. The first was followed by a Respond (the Gradual), the second by Alleluia or Tract: which is strictly in keeping with liturgical custom. When the readings were reduced to two, the Gradual and Alleluia were, left to follow one another in a haphazard way.
CURRENT SCHOLARS no longer accept this. The following comes from Dr. William Mahrt, and is printed here with permission:
HERE IS NO CONCRETE HISTORICAL EVIDENCE for a third lesson in the Roman Rite. There is, apparently, in the Milanese Rite. Perhaps the evidence that has been relied upon was the very disjunction between gradual and alleluia. Evidence against the proposed historical order (and thus the present usage of the ordinary form) is that the assignment of alleluias to the Sundays after Pentecost varies from place to place, while the other propers are quite consistent from place to place; the alleluias were unquestionably assigned after the time when a hypothetical third (unproven) reading was the case. But for the Latin Rite, there is evidence that in Augustine’s practice, there was only one lesson before the Gospel, because he preaches on the lesson, the psalm (responsorial psalm), and Gospel.
I have never seen an explanation of the “haphazard” relation of mode between gradual and alleluia. My observation in singing for the extraordinary form is that you have to calculate carefully the pitch relation between the two. I usually mark a custos at the end of the gradual, indicating the pitch of the alleluia. This, of course, presumes that the pitch of the gradual will not go down in the course of performance.
That the theory stated in Mass and Vespers has been largely been discarded is witnessed by the fact that the extensive article on alleluia in the New Grove Online by James McKinnon does not even mention the issue.
Fr. John Parsons put it this way:
S REGARDS THE OLD TESTAMENT, we are repeatedly assured that there was an Old Testament reading each Sunday morning at Mass, but that quite mysteriously these all vanished by the seventh century, and vanished leaving no memory that they had ever existed: no homilies on them by Leo or Gregory, no inadvertent cross references to them in any surviving source, not one palimpsest listing one pericope and the Sunday to which it was assigned, no tradition as to what Pope suppressed them or why; just an a priori assertion that there is a reading missing between the Gradual and the Alleluia, which would, incidentally, place the Old Testament reading after the New, contrary to practice elsewhere in the traditional Missal. This argument from silence is wildly improbable.
There are indeed Old Testament lessons on penitential days in the traditional Roman lectionary, but these are quite a different matter. The alleged set of vanished Old Testament readings are, I fear, a romantic fantasy like the vanished people’s offertory procession. They are only a theory on the lips of a liturgist, like the smile on the face of the Cheshire cat that isn’t really there. If it is now thought desirable to introduce Old Testament readings, let a new three year cycle of them be drawn up and introduced, but on an optional basis, and not on the specious ground that some element due in the liturgy had disappeared. (source)