Ninth mode

The Aeolian mode is a musical mode or, in modern usage, a diatonic scale called the natural minor scale.

The word Aeolian, like the names for the other ancient Greek tonoi and harmoniai, is an ethnic designation: in this case, for the inhabitants of Aeolis (Αἰολίς)—the Aeolian Islands and adjacent coastal district of Asia Minor. In the music theory of ancient Greece, it was an alternative name (used by some later writers, such as Cleonides) for what Aristoxenus called the Low Lydian tonos (in the sense of a particular overall pitching of the musical system—not a scale), nine semitones higher than the lowest "position of the voice", which was called Hypodorian. In the mid-16th century, this name was given by Heinrich Glarean to his newly defined ninth mode, with the diatonic octave species of the natural notes extending one octave from A to A—corresponding to the modern natural minor scale. Up until this time, chant theory recognized eight musical modes: the relative natural scales in D, E, F and G, each with their authentic and plagal counterparts, and with the option of B-flat instead of B-natural in several modes.

In 1547 Heinrich Glarean published his Dodecachordon. His premise had as its central idea the existence of twelve diatonic modes rather than eight, including a separate pair of modes each on the finals A and C. Finals on these notes, as well as on B♮, had been recognized in chant theory at least since Hucbald in the early tenth century, but they were regarded as merely transpositions from the regular finals a fifth lower. In the eleventh century Guido d'Arezzo, in chapter 8 of his Micrologus, designated these transposed finals A, B♮ and C as "affinals", and later still the term "confinal" was used in the same way. In 1525, Pietro Aaron was the first theorist to explain polyphonic modal usage in terms of the eightfold system, including these transpositions. As late as 1581, Illuminato Aiguino da Brescia published the most elaborate theory defending the eightfold system for polyphonic music against Glarean's innovations, in which he regarded the traditional plainchant modes 1 and 2 (Dorian and Hypodorian) at the affinal position (that is, with their finals on A instead of D) as a composite of species from two modes, which he described as "mixed modes". Glarean added Aeolian as the name of the new ninth mode: the relative natural mode in A with the perfect fifth as its dominant, reciting note or . The tenth mode, the plagal version of the Aeolian mode, Glarean called Hypoaeolian ("under Aeolian"), based on the same relative scale, but with the minor third as its tenor, and having a melodic range from a perfect fourth below the tonic to a perfect fifth above it.

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