sacre gestas.)
A dactylic foot consists of a long and two shorts. In contrast to the trochee (LB), which contains three
tempora (2 + 1), the normal dactyl (LBB) contains four (2 + 1 + 1), which would make it longer than a
“perfection.” To accommodate the dactylic foot to what had become the de facto ternary meter of modal
rhythm, it was stretched out over two perfections, becoming inherently a modus ultra mensuram, a “mode
beyond (normal) measure.” The first perfection was entirely occupied by the long, now perfect by
definition. The remaining perfection was divided unequally between the two breves, one of them
becoming a so-called brevis altera (“altered” or “alternate” breve) containing two tempora. Thus the six
tempora occupied by the LBB of the dactylic foot was apportioned 3 + 2 + 1 or 3 + 1 + 2, with the latter
much more frequently described (or prescribed, which amounts to the same thing) by mid-thirteenth
century theorists, and that is the pattern commonly employed in modern transcriptions, though the other is
not by any means precluded.
FIG. 6-5 Opening of Alleluia Nativitas, setas organum triplum by Perotinus (W 1 , f. 16).
One of the most widely circulated dactylic pieces is the Alleluia Nativitas, an organum triplum for
the Mass of the Feast of Mary’s Nativity (an especially important feast at “Our Lady’s” own church, Notre
Dame), attributed to Perotin in Anonymus IV. Its first page, as given in W 1 , is shown in Fig. 6-5; Ex. 6-5
is a transcription of three significant excerpts, beginning with the word “Alleluya” (Ex. 6-5a).
The basic ligature pattern for this rhythmic mode consists of a nota simplex, representing the first
perfect long, followed by a series of ternariae. This pattern is very clearly set out at the beginning of the
Alleluia Nativitas, but gives way at various points, particularly near the ends of sections, to the more
fluid trochaic pattern. (Look, for example, at “-YA,” the concluding portion in Fig. 6-4.) Remarkable in
this composition is the sheer number of rhythmically active clausulae in the verse. There are half a dozen
of them, including one (on Ex semine) that is of great historical significance for a reason we will discover
in the next chapter (Ex. 6-5b). The last clausula, on “IU-” (Ex. 6-5c), is also of special interest for the
way the 12-note tenor is put through a second cursus in diminution: irregular ordines of duplex and perfect
longs give way to an uninterrupted and self-evidently climactic run of perfect longs that end the
composition on a note of maximum excitement.
EX. 6-5A Alleluia Nativitas (attributed to Perotin), mm. 1–63