Musical modes chart: Ionian to Locrian

Overview

In music theory, the term mode or modus is used in a number of distinct senses, depending on context.

Its most common use may be described as a type of musical scale coupled with a set of characteristic melodic and harmonic behaviors. It is applied to major and minor keys as well as the seven diatonic modes (including the former as Ionian and Aeolian) which are defined by their starting note or tonic. (Olivier Messiaen's modes of limited transposition are strictly a scale type.) Related to the diatonic modes are the eight church modes or Gregorian modes, in which authentic and plagal forms of scales are distinguished by ambitus and tenor or reciting tone. Although both diatonic and Gregorian modes borrow terminology from ancient Greece, the Greek tonoi do not otherwise resemble their medieval/modern counterparts.

Previously, in the Middle Ages the term modus was used to describe intervals, individual notes, and rhythms. Modal rhythm was an essential feature of the modal notation system of the Notre-Dame school at the turn of the 12th century. In the mensural notation that emerged later, modus specifies the subdivision of the longa.

Outside of Western classical music, "mode" is sometimes used to embrace similar concepts such as Octoechos, maqam, pathet etc..

Summary

The modes can be arranged in the following sequence, which follows the circle of fifths. In this sequence, each mode has one more lowered interval relative to the tonic than the mode preceding it. Thus, taking Lydian as reference, Ionian (major) has a lowered fourth; Mixolydian, a lowered fourth and seventh; Dorian, a lowered fourth, seventh, and third; Aeolian (natural minor), a lowered fourth, seventh, third, and sixth; Phrygian, a lowered fourth, seventh, third, sixth, and second; and Locrian, a lowered fourth, seventh, third, sixth, second, and fifth. Put another way, the augmented fourth of the Lydian mode has been reduced to a perfect fourth in Ionian, the major seventh in Ionian to a minor seventh in Mixolydian, etc.

The first three modes are sometimes called major, the next three minor, and the last one diminished (Locrian), according to the quality of their tonic triads. The Locrian mode is traditionally considered theoretical rather than practical because the triad built on the first scale degree is diminished. Because diminished triads are not consonant they do not lend themselves to cadential endings and cannot be tonicized according to traditional practice.

• The Ionian mode corresponds to the major scale. Scales in the Lydian mode are major scales with an augmented fourth. The Mixolydian mode corresponds to the major scale with a minor seventh.
• The Aeolian mode is identical to the natural minor scale. The Dorian mode corresponds to the natural minor scale with a major sixth. The Phrygian mode corresponds to the natural minor scale with a minor second.
• The Locrian is neither a major nor a minor mode because, although its third scale degree is minor, the fifth degree is diminished instead of perfect. For this reason it is sometimes called a "diminished" scale, though in jazz theory this term is also applied to the octatonic scale. This interval is enharmonically equivalent to the augmented fourth found between scale degrees 1 and 4 in the Lydian mode and is also referred to as the tritone.

Usage

The usage and conception of modes or modality today is different from that in early music. As Jim Samson explains: "Clearly any comparison of medieval and modern modality would recognize that the latter takes place against a background of some three centuries of harmonic tonality, permitting, and in the 19th century requiring, a dialogue between modal and diatonic procedure." Indeed, when 19th-century composers revived the modes, they rendered them more strictly than Renaissance composers had, to make their qualities distinct from the prevailing major-minor system. Renaissance composers routinely sharped leading tones at cadences and lowered the fourth in the Lydian mode.

The Ionian, or Iastian, mode is another name for the major scale used in much Western music. The Aeolian forms the base of the most common Western minor scale; in modern practice the Aeolian mode is differentiated from the minor by using only the seven notes of the Aeolian mode. By contrast, minor mode compositions of the common practice period frequently raise the seventh scale degree by a semitone to strengthen the cadences, and in conjunction also raise the sixth scale degree by a semitone to avoid the awkward interval of an augmented second. This is particularly true of vocal music.

Traditional folk music provides countless examples of modal melodies. For example, Irish traditional music makes extensive usage not only of the major and minor (Aeolian) modes, but also the Mixolydian and Dorian modes. Within the context of Irish traditional music, the tunes are most commonly played in the keys of G-Major/A-Dorian/D-Mixolydian/E-Aeolian (minor) and D-Major/E-Dorian/A-Mixolydian/B-Aeolian (minor). Some Irish music is written in A-Major/F#-Aeolian (minor), with B-Dorian and E-Mixolydian tunes not being completely unheard of. Rarer still are Irish tunes in E-Major/F#-Dorian/B-Mixolydian.

Overview

A Gregorian mode (or church mode) is one of the eight systems of pitch organization used in Gregorian chant.

History

The name of Pope Gregory I was attached to the variety of chant that was to become the dominant variety in medieval western and central Europe (the diocese of Milan was the sole significant exception) by the Frankish cantors reworking Roman ecclesiastical song during the Carolingian period. The theoretical framework of modes arose later to describe the tonal structure of this chant repertory, and is not necessarily applicable to the other European chant dialects (Old Roman, Mozarabic, Ambrosian, etc.).

The repertory of Western plainchant acquired its basic forms between the sixth and early ninth centuries, but there are neither theoretical sources nor notated music from this period. By the late eighth century, a system of eight modal categories, for which there was no precedent in Ancient Greek theory, came to be associated with the repertory of Gregorian chant. This system likely originated from the early Byzantine oktōēchos, as indicated by the non-Hellenistic Greek names used in the earliest Western sources from about 800.