The reasons for the freedom had to do with a necessary compression. The anonymous English Caput
Kyrie, as English (but not continental) Kyries still tended to do in the fifteenth century, carried a full set of
prosulas (included in Ex. 12-4a). To accommodate them, a very spacious musical treatment was
necessary. Ockeghem, having only eighteen canonical words to set (3 × Kyrie eleison; 3 × Christe
eleison; 3 × Kyrie eleison), streamlined his setting by pruning away the lengthy internal repetitions in the
cantus firmus melody (bracketed in Ex. 12-4b), and then laying out the abridged cantus firmus to prop the
whole Kyrie in a single cursus, divided into three parts in accordance with the liturgical form, observing
both the mensuration contrast of the original Caput Mass (perfect time followed by imperfect) and the “da
capo” resumption of perfect time that was implied in the older Mass but is now made explicit.
That single cursus can be easily viewed in Fig. 12-4, which shows an “opening,” the visual unit
formed by two facing pages in a choirbook—the back or verso of one leaf (folio) and the front or recto of
the next—on which the four voice parts are entered for the group around the lectern to read from, as
Ockeghem’s own choir is shown doing in Fig. 12-2. The lower left area of the choirbook opening is the
one normally occupied by the cantus-firmus-bearing voice: the tenor, by original definition. That