that had somehow to be committed to melodic memory. Modal theory was thus one of the very many
aspects of medieval music-making that originated, very humbly, as mnemotechnics (memory aids). Every
chant was eventually assigned a modal classification in the tonaries, and eventually in the graduals and
antiphoners themselves, including the modern chant books from which some of the examples in the
previous chapters were taken. Let us now cast an eye back over some of those examples and see how
modal classification worked in practice.
In Ex. 1-1 an actual pairing of antiphon and psalm tone was given. Even though the psalm tone covers
no more than the modal pentachord (D descending to G, as it was first theoretically abstracted), the use of
C as the tuba identifies the tone as plagal, not authentic (Ex. 3-2). The antiphon is even easier to identify
as being in the eighth mode, the Hypomixolydian: its final is G, but the range extends down as far as the D
below (and exactly as far up as the D above), establishing the octave species as D to D with cadence in
the middle, on G.
Approaching the antiphon in Ex. 1-2 with a tonarist’s eye, we notice that it basically outlines the
pentachord A-down-to-D, and dips down one note below the final into the lower tetrachord. We have no
hesitation, therefore, in assigning it to the second mode, the Hypodorian. And yet the Introit antiphon in
Ex. 1-4 is unequivocally assignable to mode 1, the authentic Dorian, even though it, too, frequently makes
use of the lower neighbor to the same final. That is because the melody extends above the limits of the
modal pentachord as well, reaching the C above. The final is thus clearly located near the bottom of the
total range. The psalm verse, chosen expressly to conform to the antiphon, confirms the modal
classification. Besides the tuba on A, note the similar approaches to the high C. Here we have a case of
modal affinity of the older kind (involving turns of actual phrase) working in harness with the newer
classification: the very thing the tonarists and theorists sought to ensure.
As a matter of fact the compilers of the tonaries, and the theorists who followed them, made special
allowance for the lower neighbor to the final (called subtonium modi), especially in the protus or Dorian
tonality. As the anonymous author of Alia musica put it, “and if a note is added on to some song, above or
below the species of the octave, it will not be out of place to include this as being in the tune, not out of
it.” Thus we are to regard the low C in Ex. 1-4 to be a “note added on below” rather than a full-fledged
member of the modal tetrachord. This seeming exception to the rule about mode classification was based
on the observed behavior of mode 1 antiphons, as they existed in Pope Gregory’s inspired (and therefore
not-to-be-tampered-with) chant. Again we see the influence, even within the characteristically
rationalistic Frankish mode theory, of the older concept of mode as formula-family.
The Offertory antiphon in Ex. 1-5, although it ends on E, is only arbitrarily assigned to mode 4 (rather
than 3) by the tonarists. Clearly, it was (orally) composed with no awareness of the eventual criteria of
modal propriety, for its range partakes of tetrachords both below and above the tetrachord that descends
to the final, and it “repercusses” more on F than on either of the “Phrygian” reciting tones. Many of its
phrases, moreover, seem to belong to a different octave species altogether. Consider the second (“ut
palma florebit”), for example: it begins and ends on D, and it introduces B-flat as upper neighbor to A,
emphasizing the A as an apparent upper limit to a pentachord. This phrase by itself would unequivocally
be assigned to the first mode. Thus, where the Introit in Ex. 1-4 was a case of close correspondence
between the old Roman melody and the new Frankish theory, Ex. 1-5 shows a poor fit between the two.
Both hits and misses are equally fortuitous, for the chant evolved long in advance of the theory and quite
without premonition of it.
Proof of that fortuity comes in Ex. 1-6, the Alleluia. Phrases that closely resemble that second phrase
of Ex. 1-5 abound here (for example, the famous melisma on cedrus). Since there is no contradiction
between the internal phrases and the final cadence, it is easy to assign the melody to mode 1. (Here is the
reasoning: the lower neighbor to the final counts less as a representative of a complementary tetrachord