Vocal Music
Greek chants are composed exclusively as vocal pieces; they are not played on any instruments. Melodies that contain the characteristics of a Gregorian chant and are performed on a musical instrument or with vocal harmonies are not considered a Gregorian chant.
Melodic composition
Greek chants are composed using modal scales. This is a distinct scale that corresponds to musical compositions with only the white keys on a piano. The big and small waves we are most familiar with did not exist when Gregorian chants first appeared.
Notes
Gregorian chant music consists of rods that contain only four lines instead of the conventional five-line rods on which other music is written. In addition, Gregorian chants do not use full, half, quarter, and eighth notes that are usually found in musical notes.
Acapella
Greek chant melodies consist of a series of simple notes sung without harmonies. They are not accompanied by any additional voices or musical instruments.
Monody
Choirs that sing Gregorian chants do not divide into soprano, alto, tenor and bass voice. All voices sing the melodies in harmony. Greek chants are biblical hymns and prayers paired with melodies recited by monks from as early as the Middle Ages. The text is the most important element in Gregorian chants. Most of the texts are written in Latin and are used in the Roman Catholic Church, although some are also written in Greek.
Source:danspela.com