Louis VII was succeeded by his son Philip II in 1179 and his reign was marked by integration and revision of the cultural shifts that had transpired under his father.
It was during this time that the compositions of Pérotin first appeared, and a shift towards a more predominant discantus style.
Pérotin is best known for his composition of both liturgical organa and non-liturgical conducti in which the voices move note on note.
He pioneered the styles of organum triplum and organum quadruplum (three and four-part polyphony) and his Viderunt omnes and Sederunt principes, Graduals for Christmas and the feast of St Stephen's Day (December 26) respectively are among only a few organa quadrupla known, early polyphony having been restricted to two-part compositions.
With the addition of further parts, the compositions became known as motets, the most important form of polyphony of the period.
Pérotin's two Graduals for the Christmas season represent the highest point of his style, with a large scale tonal design in which the massive pedal points sustain the swings between consecutive harmonies, and an intricate interplay among the three upper voices.
Pérotin also furthered the development of musical notation, moving it further from improvisation.
Despite this, we know nothing of how these works came about.

In addition to his own compositions, as noted by Anonymous IV, Pérotin set about revising the Magnus Liber Organi.
Léonin's added duplum required skill, and had to be sung fast with up to 40 notes to one of the underlying chant, as a result of which the actual text progressed very slowly.
Pérotin shortened these passages, while adding further voice parts to enrich the harmony.
The degree to which he did this has been debated due to the phrase abbreviavit eundem by Anonymous IV.
Usually translated as abbreviate, it has been surmised that he shortened the Magnus liber by replacing organum purum with discant clausulae or simply replacing existing clausulae with shorter ones.
Some 154 clausulae have been attributed to Pérotin but many other clausulae are elaborate compositions that would actually expand the compositions in the Liber, and these stylistically resemble his known works which are on a much grander scale than those of his predecessor, and hence do not represent "abbreviation".
An alternative rendering of abbreviavit is to write down, suggesting that he actually prepared a new edition using his better developed system of rhythmic notation, including mensural notation, as mentioned by Anonymous IV.

Two styles emerged from the organum duplum, the "florid" and "discant" (discantus).
The former was more typical of Léonin, the latter of Pérotin, though this indirect attribution has been challenged.
Anonymous IV described Léonin as optimus organista (the best composer of organa) but Pérotin, who revised the former's Magnus Liber Organi (Great Organum Book), as optimus discantor referring to his discant composition.,
In the original discant organum duplum, the second voice follows the cantus firmus, note on note but at an interval, usually a fourth above.
By contrast, in the florid organum, the upper or vox organalis voice wove shorter notes around the longer notes of the lower tenor chant.
Louis VII was succeeded by his son Philip II in 1179 and his reign was marked by integration and revision of the cultural shifts that had transpired under his father. It was during this time that the compositions of Pérotin first appeared, and a shift towards a more predominant discantus style. Pérotin is best known for his composition of both liturgical organa and non-liturgical conducti in which the voices move note on note. He pioneered the styles of organum triplum and organum quadruplum (three and four-part polyphony) and his Viderunt omnes and Sederunt principes, Graduals for Christmas and the feast of St Stephen's Day (December 26) respectively are among only a few organa quadrupla known, early polyphony having been restricted to two-part compositions. With the addition of further parts, the compositions became known as motets, the most important form of polyphony of the period. Pérotin's two Graduals for the Christmas season represent the highest point of his style, with a large scale tonal design in which the massive pedal points sustain the swings between consecutive harmonies, and an intricate interplay among the three upper voices. Pérotin also furthered the development of musical notation, moving it further from improvisation. Despite this, we know nothing of how these works came about.
In addition to his own compositions, as noted by Anonymous IV, Pérotin set about revising the Magnus Liber Organi. Léonin's added duplum required skill, and had to be sung fast with up to 40 notes to one of the underlying chant, as a result of which the actual text progressed very slowly. Pérotin shortened these passages, while adding further voice parts to enrich the harmony. The degree to which he did this has been debated due to the phrase abbreviavit eundem by Anonymous IV. Usually translated as abbreviate, it has been surmised that he shortened the Magnus liber by replacing organum purum with discant clausulae or simply replacing existing clausulae with shorter ones. Some 154 clausulae have been attributed to Pérotin but many other clausulae are elaborate compositions that would actually expand the compositions in the Liber, and these stylistically resemble his known works which are on a much grander scale than those of his predecessor, and hence do not represent "abbreviation". An alternative rendering of abbreviavit is to write down, suggesting that he actually prepared a new edition using his better developed system of rhythmic notation, including mensural notation, as mentioned by Anonymous IV. 
Two styles emerged from the organum duplum, the "florid" and "discant" (discantus). The former was more typical of Léonin, the latter of Pérotin, though this indirect attribution has been challenged. Anonymous IV described Léonin as optimus organista (the best composer of organa) but Pérotin, who revised the former's Magnus Liber Organi (Great Organum Book), as optimus discantor referring to his discant composition., In the original discant organum duplum, the second voice follows the cantus firmus, note on note but at an interval, usually a fourth above. By contrast, in the florid organum, the upper or vox organalis voice wove shorter notes around the longer notes of the lower tenor chant.
Pérotin