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musical theory can be viewed as the sixth mode of the major scale.
Like major scales, minors are named after their tonic (first) note. However unlike majors, minor scales do not have their own set of key signatures. Instead it is necessary to use the key signature of a minor's relative major scale. The relative major is found by raising the minor tonic note by 3 semitones (an interval of a minor third); for example the relative major of E minor is G major. We know that the key signature of G major has one sharp (see major scales for how to find this,) therefore E minor also has one sharp in its key signature.
This table illustrates the relative major key signatures for minor scales.
Scales produced from just the key signature of the relative major are sometimes called natural minors, also called the Aeolian mode. The simplest natural minor scale is A natural minor:
This variant is sometimes referred to as the descending melodic minor scale as it is often used in descent from the tonic.
The ascending melodic minor scale is constructed by sharpening the 6th and 7th scale degrees of the minor scale (or, equivalently, flatting the third degree of the major scale). This variation is used primarily for ascending lines, since it has strong motion towards the tonic.
For example, in the key of A minor, the ascending melodic minor scale is:
Harmonic minors are constructed by sharpening the 7th degree of the minor scale.
For example, in the key of A minor, the harmonic minor scale is:
This scale is used in constructing harmony as it contains the major dominant chord and the minor subdominant chord.
A natural minor scale, is a scale without any accidentals in it.
For example, in the key of A minor, the natural minor scale is:
The minor scale may be considered as a variation of the major scale. For instance, the conception of the minor scale being simply a major scale with lowered or altered third, sixth, and seventh scale degrees.
The minor scale may also be considered as the sixth mode of a major scale, with its tonic starting on the sixth degree of the major scale. Alternately the major scale may be viewed as the third mode of the minor scale.
The minor third is considered the hallmark of a minor scale, since the sixth and seventh may be variably raised while the third remains unaltered. Constrastingly, changes of mode, which would involve the alteration of the third, and mode mixture, are often analyzed as relatively minor or trivial changes unless structurally supported as the root and overall key and tonality remains relatively unchanged when compared to, for instance, modulation or transposition. These latter operations are done by moving all intervals up or down a certain constant interval, and does change key, but does not change mode, which requires the alteration of intervals. The use of triads only available in the minor mode, such as the use of A♭-major in C major, is relatively decorative chromaticism, considered to add color and weaken sense of key without entirely destroying or losing it.
In the German theory by or derived from Hugo Riemann, the minor mode is considered the inverse of the major mode, an upside down major scale based on (theoretical) undertones rather than (actual) overtones (harmonics). The "root" of the minor triad is thus considered the top of the fifth, which, in the United States, is called "the" fifth. So in C minor, the tonic root is actually G, and the leading tone is A♭ (a halfstep), rather than, in major, the root being C and the leading tone B (a halfstep). Also, since all chords are analyzed as having a tonic, subdominant, or dominant function, with, for instance, in C, A-minor being considered the tonic parallel (US relative), Tp, the use of minor mode root chord progressions in major such as A♭-major-B♭-major-C-major is analyzed as sP-dP-T, the minor subdominant parallel, the minor dominant parallel, and the major tonic. (Gjerdingen, 1990)
Minor scales are sometimes said to have a more interesting, possibly sadder sound than plain major scales. The minor mode, with its variable sixth and seventh degrees, offers nine notes, in C: C-D-Eb-F-G-A♭-A-B♭-B, over majors' seven, in C: C-D-E-F-G-A-B. The interval strength, or lowest possible location in the harmonic series, and thus consonance and "stability", of minor triads is less than that of major, which interprets major as more "stable", a major triad being found in the 4th, 5th, and 6th harmonics of a pitch, while the minor being the 5th, 6th, and 7th. This may explain the piccardy third, the use of a major tonic chord at the very end of a composition in minor, since it would be more stable and thus conclusive.