<P> Gregorian chant was originally used for singing the Office (by male and female religious) and for singing the parts of the Mass pertaining to the lay faithful (male and female), the celebrant (priest, always male) and the choir (composed of male ordained clergy, except in convents). Outside the larger cities, the number of available clergy dropped, and lay men started singing these parts . The choir was considered an official liturgical duty reserved to clergy, so women were not allowed to sing in the Schola Cantorum or other choirs except in convents where women were permitted to sing the Office and the parts of the Mass pertaining to the choir as a function of their consecrated life . </P> <P> Chant was normally sung in unison . Later innovations included tropes, which is a new text sung to the same melodic phrases in a melismatic chant (repeating an entire Alleluia - melody on a new text for instance, or repeating a full phrase with a new text that comments on the previously sung text) and various forms of organum, (improvised) harmonic embellishment of chant melodies focusing on octaves, fifths, fourths, and, later, thirds . Neither tropes nor organum, however, belong to the chant repertory proper . The main exception to this is the sequence, whose origins lay in troping the extended melisma of Alleluia chants known as the jubilus, but the sequences, like the tropes, were later officially suppressed . The Council of Trent struck sequences from the Gregorian corpus, except those for Easter, Pentecost, Corpus Christi and All Souls' Day . </P> <P> Not much is known about the particular vocal stylings or performance practices used for Gregorian chant in the Middle Ages . On occasion, the clergy was urged to have their singers perform with more restraint and piety . This suggests that virtuosic performances occurred, contrary to the modern stereotype of Gregorian chant as slow - moving mood music . This tension between musicality and piety goes far back; Gregory the Great himself criticized the practice of promoting clerics based on their charming singing rather than their preaching . However, Odo of Cluny, a renowned monastic reformer, praised the intellectual and musical virtuosity to be found in chant: </P> <P> For in these (Offertories and Communions) there are the most varied kinds of ascent, descent, repeat..., delight for the cognoscenti, difficulty for the beginners, and an admirable organization...that widely differs from other chants; they are not so much made according to the rules of music...but rather evince the authority and validity...of music . </P>

The official music of the catholic church during the middle ages is called