Definition
The church modes (or Gregorian modes) are the system the Middle Ages used to classify liturgical chant. They are not simply “scales starting on different notes”: each mode is defined by a finalis (the note on which the melody ends), an ambitus (the melody's range), and a reciting tone (the most repeated note, also called the tenor or repercussio). The classical system has eight modes, organized in four pairs.
Authentic and plagal
- The authentic modes (odd numbers) have an ambitus that runs from the finalis to the octave above.
- The plagal modes (even numbers, prefix hypo-) share the same finalis, but the ambitus runs from a fourth below to a fifth above: the finalis sits in the middle of the melody.
| Mode | Name | Finalis | Ambitus | Reciting tone |
|---|---|---|---|---|
| I | Authentic Protus (Dorian) | D | D–D | A |
| II | Plagal Protus (Hypodorian) | D | A–A | F |
| III | Authentic Deuterus (Phrygian) | E | E–E | C |
| IV | Plagal Deuterus (Hypophrygian) | E | B–B | A |
| V | Authentic Tritus (Lydian) | F | F–F | C |
| VI | Plagal Tritus (Hypolydian) | F | C–C | A |
| VII | Authentic Tetrardus (Mixolydian) | G | G–G | D |
| VIII | Plagal Tetrardus (Hypomixolydian) | G | D–D | C |
Rule of thumb: in the authentic modes the reciting tone is a fifth above the finalis (except in mode III, where the fifth would be the unstable B and it moves up to C); in the plagal modes it is a third below that of the corresponding authentic mode (with exceptions when it would land on B).
B-flat and musica ficta
In practice the B could be lowered to avoid the tritone with F. In mode V (Lydian) the Bb is so frequent that the mode often sounds like F major. In mode I the Bb gives the Dorian the color of natural D minor. Singers also added other unwritten accidentals (musica ficta), mainly to create leading tones at cadences.
Glareanus and the twelve modes
In 1547 the Swiss theorist Glareanus, in his treatise Dodecachordon, added four modes: Aeolian (finalis A) and Hypoaeolian, Ionian (finalis C) and Hypoionian. Aeolian and Ionian are the direct ancestors of our minor and major. The Locrian (finalis B) remained theoretical, because of the diminished fifth above the finalis.
Differences from modern modes
- In modern modes (jazz, pop) what matters is the color of the scale over a root; in the church modes what matters is the melodic behavior: where the melody pauses, where it recites, how far it extends.
- A plagal mode and its authentic counterpart have the same notes and the same finalis: only the position of the melody changes.
- Two chants in different modes can have the same ambitus (modes I and VIII both move between D and D): what distinguishes them is the finalis, D in the first and G in the second.
Common mistakes
- Thinking the Hypodorian is a “scale from A”: the finalis remains D.
- Ignoring the reciting tone: it is the note that gives the mode its identity to the ear.
- Applying the modern leading tone (C# in mode I) everywhere: it distorts the mode; in early music it is used only at cadences.
Examples
- Dies irae: a Gregorian sequence in mode I (Dorian), quoted by Berlioz, Liszt, Rachmaninoff, and in many film scores.
- Pange lingua: a hymn in mode III (Phrygian).
- Veni Creator Spiritus: a hymn in mode VIII.
- Quasi modo geniti: an introit in mode VI.
- Vaughan Williams, Fantasia on a Theme by Thomas Tallis: the Tallis theme is in the third mode, the Phrygian, and its archaic color pervades the entire composition.
How to use it in composition
- To evoke the sacred or the medieval, choose a finalis and a reciting tone and build the melody around them, moving by step and with a limited ambitus.
- Write a plagal melody (finalis in the middle) for an introspective character, an authentic one (finalis at the bottom) for a more open, ascending character.
- When harmonizing, avoid the dominant with a leading tone: use diatonic triads of the mode and cadences with contrary motion between the voices.
Exercise
- Write a ten-note melody in authentic mode I and one in plagal mode II with the same finalis, D.
- Find the reciting tone in a Gregorian melody and count how many times it appears.
- Harmonize a phrase in mode VII without using F#.
Connections
Dorian mode; Phrygian mode; Lydian mode; Mixolydian mode; The modes of the major scale; Origins of notation; First-species counterpoint; Sacred forms: the mass and the motet.