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The Eight "Gregorian" Modes

Here by popular request, this page is dedicated to an explanation of the eight "Gregorian" modes. The names of mediæval theorists and treatises marked up with hypertext lead to the complete text of the treatise in the original Latin located at THESAURUS MUSICARUM LATINARUM at Indiana University.

The system of dividing the chant repertory into eight modes had its origins in the eight "echoi" of the Byzantine chant of the Eastern Church.  In the Byzantine system, the "echoi" are melodic types, and thus a "mode" is primarily a property of a particular "tune-family".  The division of Western chant into eight modes was adapted from this, but the Western repertory existed before the eight-mode classification system was applied to it, and it had not originally been so conceived.  In consequence, the eight modes functioned in the West more as pre-existent "scales" to which individual chants had to be assigned.  The Frankish "Gregorian" chant is not the only form of Western Plainchant, although it has since supplanted all but the Milanese "Ambrosian" chant, which is still sung in Milan today. Before the triumph of "Gregorian" chant, however, there was a variety of Western chant traditions, including Old Beneventan, Milanese "Ambrosian", Old Spanish "Mozarabic", Gallican and Old Roman. Of these only the Frankish "Gregorian" chant adopted the theoretical system of eight modes.

There are eight different "official" church modes (which is not to say that the modality of every chant can be explained by one of the eight). In fact, it might be truer to say that there are four pairs of modes, each pair sharing the same "final", which may in some respects be compared with the keynote of a major or minor scale. The four pairs, with finals on D, E, F and G respectively, can be played on the white notes of a modern keyboard. However, it is important to stress that the modes, unlike modern scales, are not of fixed pitch. They are, rather, particular arrangements of tones and semitones, which can be sung at any pitch:

  1. DEFGabcd
  2. EFGabcde
  3. FGabcdef
  4. Gabcdefg
The difference between the two members of each pair is concerned principally with two things: (1) which other notes beside the final are structurally important in melodies assigned to the mode in question, and (2) the melodic range of melodies assigned to the mode. The simplest chant for demonstrating (1) is a psalm tone. In the Divine Office, "Gregorian" psalmody is sung in conjunction with antiphons. An antiphon is a short text, often taken from the text of the psalm with which it is used, sung before and after the reciting of the psalm itself. The melody of the antiphon, its range and final, determine its assignment to a mode, and the mode of the antiphon in turn determines the tone to which the accompanying psalm is recited. The predominating "reciting" note in any psalm tone is also, beside the final, the second structurally important tone in the mode.  The list of eight modes below shows how each of the four of the above list can be differentiated into two separate modes, both sharing the same final. Reciting notes appear as bold characters, finals in Italics. The first pair below, for example, share the final "D", but each has a different melodic range and reciting note, the first reciting on "a", the second on "F". Note that the even-numbered modes have a smaller range between final and reciting note. As a result melodies assigned to these modes tend to have a narrower melodic range than those assigned to the odd-numbered modes:
  1. DEFGabcd
  2. ABCDEFGa
  3. EFGabcde
  4. BCDEFGab
  5. FGabcdef
  6. CDEFGabc
  7. Gabcdefg
  8. DEFGabcd

Terminology

There are various terminologies associated with this "eight-mode system". The easiest and most obvious is that employed in the modern official chant books of the catholic church , in which the modes are simply numbered 1-8 in Roman numerals. However, other nomenclature, based upon different mediæval theorists, is also frequently encountered. One of these, familiar to Hucbald (c. 840-930), to the ninth-century authors of the treatises Musica Enchiriadis and Scolica Enchiriadis , to Aurelian of Réôme (fl. 840-50) and to the author of the ninth-tenth century Commemoratio Brevis de Tonis et Psalmis Modulandis , is first found in a late eighth-early ninth century tonary from S. Riquier (Paris, Bibliothèque Nationale, lat. 13159), which lists four modes: "protus", "deuterus", "tritus" and "tetrardus" (respectively, the Greek words for first, second, third and fourth), and subdivides each of the four into two, the first of each pair being designated "authentus" ("authentic") and the second "plagis" ("plagal"):

  1. Protus authentus
  2. Protus plagis
  3. Deuterus authentus
  4. Deuterus plagis
  5. Tritus authentus
  6. Tritus plagis
  7. Tetrardus authentus
  8. Tetrardus plagis
If anything suggests that the system of eight modes was derived from the East, this is surely it, since the terminology is markedly similar to that of the Byzantine modes. In addition, melodic formulæ with strange "nonsense" texts to exemplify the characteristics of each mode are sometimes found in Byzantine chant. Certain Western tonaries employed similar formulæ with pseudo-Greek texts:
  1. No-an-no-e-a-ne (a-G-FE-G-FED-D)
  2. No-e-a-gis (DCDEF-G-FE-D)
  3. No-i-o-e-a-ne (G-abc-b-a-Ga-E)
  4. No-e-a-is (EFGFEG-Ga-FG-E)
  5. No-i-o-e-a-ne (c-c-cba-c-G-F)
  6. No-e-a-gis (EFDCF-Ga-G-F)
  7. No-i-o-e-a-ne (d-d-c-c-da-G)
  8. No-e-a-gis (a-accb-aG-G)
However, perhaps more familiar to modern consciousness because of its adoption in discussions of Anglo-Celtic "folk" modality, there is also another Greek terminology for the modes, derived from the place-names which ancient Greek music theory associated with the various modes, knowledge of which has passed to the modern world largely thanks to the writings of Boethius (c. 480-c. 524). According to Boethius, the names were applied to ancient Greek modes corresponding roughly to the "Gregorian" modes, as follows:
  1. Phrygian
  2. Hypodorian
  3. Dorian
  4. Mixolydian
  5. Hypolydian
  6. Lydian
  7. Hypophrygian
  8. (There would appear to be no equivalent in this system to mode 8.)
This terminology was "incorrectly" reapplied to the "Gregorian" repertory in the late ninth century treatise Alia Musica as follows:
  1. Dorian
  2. Hypodorian
  3. Phrygian
  4. Hypophrygian
  5. Lydian
  6. Hypolydian
  7. Mixolydian
  8. Hypermixolydian
This is the terminology most frequently encountered in discussions of British "folk" music modality. Further mode-names, also based upon ancient Greek place-names, were added by Glareanus (1488-1563):  the "Aeolian", "Locrian" and "Ionian" modes, which can be played on the "white" notes of a keyboard by beginning, respectively, on A, B and C.  The "Locrian" mode was originally posited by Glareanus to "explain" chants outside the eight-mode system reciting and ending on "B", for example, the earlier version of the antiphon "Cantabimus" cited below, ending on a "B".  The Locrian mode would have been problematic in the Middle Ages, in that it would imply the existence of a mode with a final on "B" and a reciting-note on "F", the two notes being a diminished 5th apart, the "diabolus" in music.  (Pop music musicologists find the term "Locrian" useful in discussing "heavy metal" rock music, where this interval, and the scale ending on "B", are commonplace!)  The real explanation for the existence of the chants assigned by Glareanus to the "Locrian" mode, however, is that this mode was one used before the invention of the eight-mode system.  Most chants reciting and ending on "B" were later altered to fit the eight-mode system, but a few retained their early form, and thus came to the notice of Glareanus.

Before the eight-mode system

However, the chant repertory was conceived before the adoption of the eight-mode system. I will conclude by suggesting various ways (there may be others) by which this may be ascertained.

1. The only "accidental" allowed in later pitch-defined chant notation was the B flat, but some chants evidently required an E flat as well (or F sharp, depending how the chant was transposed). The refusal of certain chants to fit the eight-mode system gave rise to discussions of problem chants in the writings of various mediæval theorists, sometimes suggesting a willingness to alter the chant to make it fit modal theory. An early source, Montpellier, Faculté de Médecine, MS. H. 159 ("The Dijon Tonary", published by Solesmes in the Paléographie Musicale series) is useful in containing a dual notation, recording both the manner of performance in early non-pitch-defined neumes, as well as the pitches in letter notation. The pitch notation in this manuscript records, for example, switches between the B natural and B flat during the course of a piece. It can sometimes illustrate the nature of some of the "problems" which occupied the minds of the mediæval theorists.

2. There is some evidence of the alteration of melodies to make them conform to the eight-mode system. Some early "Gregorian" sources contain antiphons for psalms which do not conform to the system, and it is sometimes possible to see that "the same" melody has later been altered to ensure its conformity, e.g. two forms of the melody for the antiphon "Cantabimus et psallemus virtutes tuas, Domine" can be found:

The later version has been assigned to mode 8, ending on "G"; the earlier, however, ends on "b", and moreover the psalm tone associated with it recites on the same note, so that reciting-note and final are one and the same. It has also been suggested that modes which recite and end on the same note are of considerable antiquity. Gélineau suggests that the mode reciting and ending on "b" has counterparts in the traditional chant of both Eastern and Western rites of the Christian church, and that it may therefore be descended from a responsorial psalm form in the early church. It may be indicative of this that certain responsory tones still in use in the "Gregorian" repertory which cannot be assigned to one of the eight modes are similar to certain of the irregular antiphon melodies and their psalm tones. It has always been the aim of the Solesmes monks, who produce the official chant books for the modern catholic church, to "restore" the "Gregorian" melodies to their "original" form (whether or not one believes this to be possible!). Both the recent Psalterium Monasticum and volume 2 of the new Antiphonale Romanum reflect the Solesmes monks' concern to "restore" modalities in use before the imposition of the eight-mode system.

3. The Old Roman chant and the Frankish "Gregorian" version of it are related, but also different in detail. The two versions can be compared to two variant forms of "the same" orally transmitted "folk" tradition. One significant difference between the Frankish and the Old Roman is that, in contrast to the eight modes and eight psalm-tones of the Frankish chant, the two surviving Old Roman antiphoners contain over a hundred psalm-tones between them. There was clearly no assignment of antiphon melodies to eight different ways of singing the psalms in Rome; rather there was a considerable fluidity. Thus it is suggested that the more rigid eight-mode system was imposed upon the Roman repertory after its adoption by the Franks. In the Old Roman chant, however, not only are there a large number of psalm tones in the two surviving antiphoners, only a half are common to both books. This lack of codification is probably due to the Roman chant's having continued as an oral tradition right up to the eve of its supplantation by the Frankish "Gregorian" version, whereas the earlier, written codification of the Frankish version seems to have frozen its development.

4. Another indication that the eight-mode system was applied to the chant repertory after it had already existed for some time is the fact that sometimes two chants using "the same", or at least a similar, melodic type, can be assigned to different modes, for example:

Some antiphons of this melodic type differ from each other only in whether the degree of the scale above the final is a tone or a semitone. This suggests that the melodies may have originally been identified as "tune families", rather than have been classified into the pre-existing arrangements of tones and semitones of the eight-mode system.