There are large sections devoted to spare parts like these, sometimes called “substitute clausulas” or
“ersatz clausulas,” in all four major Notre Dame codices. (In addition to Flo, W 1 , and W 2 , there is a
slightly smaller one called Ma, roughly contemporaneous with W 2 , copied in Spain for the cathedral at
Toledo, and now kept at the National Library in Madrid.) They raise tantalizing questions about the nature
of this music, its transmission, and its history.
Every piece in the so-called Magnus Liber—the “great book” attributed to Leonin by Anonymus IV—
exists, as we have observed in the case of Viderunt omnes, in significantly different versions in its
various sources, and since all the extant written sources were copied at least two or three generations,
and in some cases as much as a century, after the purported time of Leonin, it is impossible to determine
what the original form of any of these pieces was. And every piece in the Magnus Liber is equipped with
a multitude of interchangeable parts like the clausulae we have observed on “Do-.” Besides the ones on
“Do-,” the Notre Dame codices contain interchangeable Viderunt clausulas on the tenor fragments “om-”
(from omnes), “su-” (from suum) in the verse, and even on “conspectum gentium” from the verse, which
is not a melisma.
One can only conclude that the identity of a “piece of music” was a far more fluid concept for the
Notre Dame cantors than it is for us. An organum as actually performed was essentially a patchwork
created more or less on the spot, or after a brief consultation, from the many available parts in the
manuscripts we have (and who knows how many others that were never entered in those lucky survivors
or—now here’s a thought—that were never written down at all).
Even if we limit the choice to what is written and what is extant, it is nevertheless hard to imagine the
Notre Dame cantors furiously leafing forward and back through their books during the service to find the
clausulas they wished to perform on a given day. And as we have already observed about the earliest
chant books, the Notre Dame codices, while “immense” (as noted above) in terms of their total contents,
were tiny in actual physical dimensions. The actual written area of a page from W 1 measures
approximately 51/2 × 21/2 inches, while Flo, the largest, measures approximately 61/4 by 4. A
musicologist in her study, working at leisure, has to squint at W 1 to make its bitsy flyspecks out; one can
hardly assume that such a book could have been used in the act of performing. The assumption has to be,
rather, that the Notre Dame cantors, and anyone else who sang their music in the dark confines of a
medieval church, performed from memory.
The question of memory once again opens out quickly onto a much larger, more critical terrain. There
are absolutely no written sources of Notre Dame polyphony from the period from the 1170s to the 1190s,
when Anonymus IV’s Leonin supposedly lived and worked (or, for that matter, when Professor Wright’s
Leonius actually lived and worked). All the extant sources postdate the lifetime of Anonymus IV’s Perotin
as well, even if we grant Perotin the longest conceivable life span (say, to the time of Philip the
Chancellor’s death in 1236). The sources were all written between the 1240s and the 1280s, and the
author of Anonymus IV, as well as all the other theorists of “modal rhythm” and its notation, lived and
worked around the same time.
A strong suspicion arises from these circumstances that the organa dupla of the so-called Magnus
Liber were not part of a liber at all during their period of greatest use, but were created, sung, and
transmitted from singer to singer within what was, yes, still predominantly an oral culture. Far from
adding to the mystery of this music, however, the assumption of an oral tradition actually suggests the best
answer to the riddle of how Notre Dame polyphony came to be the epoch-making thing it was—namely,
the first “measured music” in the West.
Now it is time to pose explicitly the questions that have been stalking our discussion of modal rhythm
from the beginning: What was its purpose? What did it accomplish? Often it is claimed that the Notre