<P> Chants sometimes fall into melodically related groups . The musical phrases centonized to create Graduals and Tracts follow a musical "grammar" of sorts . Certain phrases are used only at the beginnings of chants, or only at the end, or only in certain combinations, creating musical families of chants such as the Iustus ut palma family of Graduals . Several Introits in mode 3, including Loquetur Dominus above, exhibit melodic similarities . Mode III (E authentic) chants have C as a dominant, so C is the expected reciting tone . These mode III Introits, however, use both G and C as reciting tones, and often begin with a decorated leap from G to C to establish this tonality . Similar examples exist throughout the repertory . </P> <P> The earliest notated sources of Gregorian chant (written ca . 950) used symbols called neumes (Gr . sign, of the hand) to indicate tone - movements and relative duration within each syllable . A sort of musical stenography that seems to focus on gestures and tone - movements but not the specific pitches of individual notes, nor the relative starting pitches of each neume . Given the fact that Chant was learned in an oral tradition in which the texts and melodies were sung from memory, this was obviously not necessary . The neumatic manuscripts display great sophistication and precision in notation and a wealth of graphic signs to indicate the musical gesture and proper pronunciation of the text . Scholars postulate that this practice may have been derived from cheironomic hand - gestures, the ekphonetic notation of Byzantine chant, punctuation marks, or diacritical accents . Later adaptations and innovations included the use of a dry - scratched line or an inked line or two lines, marked C or F showing the relative pitches between neumes . Consistent relative heightening first developed in the Aquitaine region, particularly at St. Martial de Limoges, in the first half of the eleventh century . Many German - speaking areas, however, continued to use unpitched neumes into the twelfth century . Additional symbols developed, such as the custos, placed at the end of a system to show the next pitch . Other symbols indicated changes in articulation, duration, or tempo, such as a letter "t" to indicate a tenuto . Another form of early notation used a system of letters corresponding to different pitches, much as Shaker music is notated . </P> <P> By the 13th century, the neumes of Gregorian chant were usually written in square notation on a four - line staff with a clef, as in the Graduale Aboense pictured above . In square notation, small groups of ascending notes on a syllable are shown as stacked squares, read from bottom to top, while descending notes are written with diamonds read from left to right . When a syllable has a large number of notes, a series of smaller such groups of neumes are written in succession, read from left to right . The oriscus, quilisma, and liquescent neumes indicate special vocal treatments, that have been largely neglected due to uncertainty as to how to sing them . Since the 1970s, with the influential insights of Dom Eugène Cardine (see below under' rhythm'), ornamental neumes have received more attention from both researchers and performers . B - flat is indicated by a "b - mollum" (Lat . soft), a rounded undercaste' b' placed to the left of the entire neume in which the note occurs, as shown in the "Kyrie" to the right . When necessary, a "b - durum" (Lat . hard), written squarely, indicates B - natural and serves to cancel the b - mollum . This system of square notation is standard in modern chantbooks . </P> <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>

Which composer was renowned for creating expressive gregorian chants