The payoff comes at the end. The last phrase of the canon begins with the Bassus’s “Dona nobis
pacem” in m. 40. Its progression from the final (I) to the subsemitonium or leading tone (vii) by way of an
initial descent to the subdominant or lower fifth (IV) elegantly prepares the final cadence in the second
Cantus a ninth above: supertonium (ii) to the long-held final (I) by way of an initial descent to the tuba
(V). These sequences of degree functions, modeled on those of the ground basses and reinforced by
constant use, were eventually stereotyped into the familiar tonal cadences of what we, looking back on it,
call the “common practice.” Palestrina’s I–IV–vii//ii–V–I, arising out of his strange canon-by-two-fifths,
is none other than the essential frame of the common-practice circle of fifths, lacking only the middle pair
(iii–vi) for completion.
EX. 16-12B Giovanni Pierluigi da Palestrina, Missa Papae Marcelli, Agnus II, mm. 40–53