In 1563 Guerrero published a book of Magnificat settings to the eight tones (consisting of polyphonic music for the odd-numbered verses to alternate with the chanted even-numbered ones) and also a companion set in which the polyphony takes over the even-numbered verses. Thus Guerrero’s complete set consisted of sixteen Magnificats. In 1584, in his Liber Vesperarum
, Guerrero republished some of these versions, revised (even recomposed in places) and with some new combinations of the verses. The 1584 version of the odd-verse Magnificat upon the eighth tone alternates with chant as usual but, at the end, the alternation is broken at the Lesser Doxology, ‘Gloria Patri …’ and ‘Sicut erat in principio …’ both being polyphonic; the former is for the standard four voices but in triple time, while the ‘Sicut erat …’ reverts to the duple measure and is expanded to six voices, the extra tenor carrying the chant melody while the first tenor is followed by the second treble part in imitative canon at the octave above—a splendid conclusion.
from notes by Bruno Turner ę 1999