FIG. 6-3B Viderunt omnes set as organum duplum, perhaps by Leoninus, as the first item in Magnus liber de gradali et
antefonario (Florence, Biblioteca Medicea Laurenziana, Plut. 29. I, fols. 99-99 v; this source will be abbreviated Flo in
subsequent references).
Putting that information together with the polyphonic setting reveals that the composer set as organum
only the soloist’s portion of the chant. The two-voice polyphony thus represents a multiplied soloist, so to
speak. The parts sung by the choir are not set but were supplied in performance from memory. Since the
choristers did not need to learn their part from the book, the book does not contain their part. Materials
were expensive and space was at the highest premium.
From all of this we learn that polyphony at Notre Dame was the art of virtuoso soloists—the cantor
and his assistant, the succentor. (And that is why only responsorial chants—matins responsories,
Graduals, Alleluias—were set as organum there.) The astonishingly expansive treatment of the incipit is
something of a counterpart to the illuminated capital: a rich decoration.
Again comparing the chant in Fig. 6-3a with the organum in Fig. 6-3b, we notice that when the
soloist’s portion of the chant has its own melismas (at “om-” of omnes and especially at “Do-” of
Dominus in the verse), the organum tenor notes are written in clumps, taking up far less space (=time).
The primary motivation for hurrying the tenor along at such spots was undoubtedly practical: just imagine
how long the music would have to last if every tenor note were held out like the first few! But what begins
in necessity often ends in play—that is, in “art.” It was precisely these hurried-along sections of the
organum, where the tenor is melismatic, that evoked from the composers what we would call the greatest
artfulness or creativity. We will be tracing the repercussions of that creative response for the next three
chapters.
The ratio of notes in the duplum to notes in the tenor in such sections becomes much closer; we are
now obviously dealing with a type of discant. It is here, too, that we are most apt to find the clear
organization of ligatures in the duplum voice into “modal” patterns, invoking the abstract metrical
schemes described above.
From this we learn that in organum duplum or organum per se, the kind associated in Anonymus IV
with the name of Leonin, measured rhythm is essentially an aspect of discant. In sections where the tenor
is held long, called organum purum—“pure (or plain) organum”—to distinguish it from the discant, the
rhythm is not organized in this way. The notes are sung “freely,” as in chant. But not entirely freely, of