Aeolian mode

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The Aeolian mode comprises a musical mode or diatonic scale.

An Aeolian mode formed part of the music theory of ancient Greece, based around the relative natural scale in A (that is, the same as playing all the 'white notes' of a piano from A to A). Greek theory called this simple scale the hypodorian mode, and the aeolian and locrian modes must have formed different (perhaps chromatic) variations of this.

The term Aeolian mode fell into disuse in mediaeval Europe, as church music based itself around eight musical modes: the relative natural scales in D, E, F and G, each with their authentic and plagal counterparts.

In 1547 Heinrich Glarean published his Dodecachordon. His premise had as its central idea the existence of twelve diatonic modes rather than eight. It seems that popular folk music used the additional modes, but they did not form part of the official church repertoire. 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 tenor. The tenth mode, the plagal version of the aeolian mode, Glarean called hypaeolian ("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.

As polyphonic music replaced mediaeval monophonic church music, the folk modes added by Glarean became the basis of the minor/major division of classical European music: the aeolian mode forming the natural minor mode.

The aeolian mode consists of the same components as the major mode with the minor's sixth scale degree as its tonic. Examples include:

C Aeolian mode — the E♭ major scale starting on C; the key signature has three flats.
G Aeolian mode — the B♭ major scale starting on G; the key signature has two flats.
D Aeolian mode — the F major scale starting on D; the key signature has one flat.
A Aeolian mode — the C major scale starting on A; the key signature has no sharps or flats.
E Aeolian mode — the G major scale starting on E; the key signature has one sharp.
B Aeolian mode — the D major scale starting on B; the key signature has two sharps.
F# Aeolian mode — the A major scale starting on F#; the key signature has three sharps.
C# Aeolian mode — the E major scale starting on C#; the key signature has four sharps.

The Aeolian mode's intervallic formula when compared to the major scale consists of flatting the 3rd, 6th, and 7th scale degrees.

As the Aeolian mode forms the natural Minor scale (also known as the descending melodic minor scale), it is among the most frequently used diatonic modes in western music. Tunes entirely in the Aeolian mode (i.e., those that do not also use the ascending melodic minor scale) are rare in classical music. However, they are common in many folk traditions, including Jewish and Israeli folk music, and the Israeli national anthem Hatikvah. The A section of the Doctor Who theme tune is another example.

[edit] Aeolian "flat 5"

This chromatically-altered mode is also known as "Locrian sharp 2", Mode VI of the melodic minor scale, or the half diminished scale. It is frequently used in jazz and rock. The latter term is generally avoided by musicians, to avoid confusion with the diminished scales (see octatonic), and the half-diminished seventh chord.