A minor scale in music theory is generally any scale that includes at least three essential scale degrees: one being the tonic, another at an interval of a minor third above the tonic, and another at an interval of a perfect fifth above the tonic, together composing the tonic minor triad. While this definition encompasses many scales and modes such as Dorian mode and the Phrygian mode, the term in its stricter sense is usually limited to the natural minor, harmonic minor, and melodic minor scales, described below, which are in most common use in Western classical music (see major and minor).
The natural minor scale is the sixth mode (or Aeolian mode) of the major scale. For example, the white notes of a keyboard if played from any C continuing up an octave to the next C produce a C major scale. If the white notes are played beginning from the sixth step of that C scale, from any A to an A an octave above, then an A natural minor scale (the "relative minor" of C) is produced.
Harmonic and melodic minor
The above considerations of chordal harmony led to the harmonic minor scale, the same as the natural minor but with a chromatically raised seventh degree.
Harmonic Minor Scale: 1 2 ♭3 4 5 ♭6 7 8
For example, in the key of A minor, the harmonic minor scale is:
A B C D E F G♯ A'
An important characteristic of the harmonic minor scale—in contrast to the natural minor—is its inclusion of two sets of chords whose inversions are structurally identical, and hence have ambiguous tonality. These are the Diminished seventh chord (found on the 2nd, 4th, 6th and 7th degrees) and the Augmented chord (found on the 3rd, 5th and 7th degrees).
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