The Gregorian Modes, also known as church modes, are the eight structures of pitch organization that are used in the Gregorian Chants. Pope St. Gregory the Great is often associated with the various chants that were to become the ascendant variety during the medieval times in central and Western Europe by the Frankish cantors who reworked Roman ecclesiastical song in the Carolingian period. The theoretical structure of modes emerged later to illustrate the tonal framework of this chant repertory.
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The system of categorizing the chant repertory into eight modes can trace its roots in the eight melodic types (“echoi”) of the Eastern Church’s Byzantine chant. In the Byzantine arrangement, a mode is basically an attribute or feature of a specific tune-family. The eight modes that categorize the Western chant were adapted from this. However, the Western repertory was there even before the eight-modes system of classification was applied to it. As a result, the eight modes served in the West largely as pre-existent scales to which the individual chants were assigned.
Officially, there are eight distinct Gregorian modes, but this doesn’t mean that the modalities of each chant can be described by one of the eight. Precisely, there are four pairs of the modes, with each pair sharing a similar “final”, which is somewhat comparable with the keynote of a minor or major scale. Each of the pairs has a final on D, E, F and G, and they can be played on white notes of the modern piano keyboard. It is worthwhile to stress the fact that the eight modes do not have fixed pitch like modern scales. In essence the eight tones are rather specific arrangements or orders of tones and semi-tones that can be sung at any pitch.
The two units of each pair can be distinguished on the basis of two principles.
1#: The first principle is which sets other notes apart from the final are fundamentally important in the melodies attached to the mode concerned.
2#: The second principle is the melodic bounds or spectrum of melodies that are attached to the mode.
A psalm tone is the most basic chant for demonstration. Gregorian psalmody is normally sung along with antiphons, which are short texts that are often obtained from text in the book of psalms. The antiphons can be sung before, as well as after reciting the psalm. The antiphon’s melody, its bounds, and its final will determine its attachment to a particular mode. In turn, the antiphon’s mode will determine the tone to which the corresponding psalm is recited.
The system of eight modes is usually associated with various terminologies. The most basic and most apparent is that used by Catholic Church in its contemporary official chant books, whereby the eight modes are typically numbered 1 to 8 in Roman digits. However, other classification, based on various medieval thinkers, is also encountered frequently. One example is first encountered in a late 8th to early 9th century tones which list four modes named protus, deuterus, tritus and tetrardus (Greek words for 1st, 2nd, 3rd, and 4th). Each of the four modes are further subdivided into two, whereby the first of each pair is designated authentic (“authentus”), while the second pair are designated plagis or plagal. See example below:
- Protus authentus
- Protus plagis
- Deuterus authentus
- Deuterus plagis
- Tritus authentus
- Tritus plagis
- Tetrardus authentus
- Tetrardus plagis
There is nothing that confirms more that the eight mode system was adapted from the church in the East than this. The terminology conspicuously resembles that of the Byzantine modes. Additionally, there are other more subtle elements of specific Western tones that employ the same formula.