The Missa Ad coenam Agni
is based on a plainsong Hymn dating probably from the seventh century. Palestrina also set this Hymn for use in the Office liturgy: this setting is not related to the Mass other than through its use of the same chant melody. As is customary in polyphonic Hymns, Ad coenam Agni providi
is set alternatim, with the odd-numbered verses being selected for polyphonic treatment in this case. There are therefore four polyphonic verses interspersed with three sung to the chant, and Palestrina achieves a remarkable level of variety in treating the tune. The first verse commences in close imitation, with bassus introducing the second strain of the melody (the first having been intoned monophonically), followed by altus, cantus, and finally tenor, which states the chant almost without amendment, before the cantus takes it over at ‘Post transitum maris rubri’ (‘after crossing the Red Sea’). The second polyphonic verse is similarly imitative in style, but on a much broader scale: the chant melody is again heard most obviously in cantus and tenor, but with a greater degree of elaboration. The third verse is largely homophonic, with a striking cadence on E (sounding D at performing pitch) at ‘plebs captivata’ (‘a captive people’). The final verse expands to five voices with the addition of a second tenor, and is the longest and most exuberant of the four.
from notes by Stephen Rice © 2013