A minor scale in music theory is a diatonic scale with a third scale degree at an interval of a minor third above the tonic. While this definition encompasses modes with the minor third, such as Dorian mode, the term may more usually refer only 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 same as the 6th musical mode of the major scale (the Aeolian mode). For example, the white notes of a keyboard give a major scale from C to C. If the notes are played beginning from the sixth step of that scale, which is A, then a natural minor scale (the "relative minor" of C) is heard.
One may therefore remember the steps in the natural minor scale - "W,H,W,W,H,W,W," (in semitones - 2 1 2 2 1 2 2) - as just the familiar major scale steps with a different starting point. C major is C D E F G A B C; the A natural minor scale is A B C D E F G A. If the scale is used with the correct corresponding key signature, the natural minor scale needs no accidentals.
The natural minor scale is the same as the Aeolian mode, but music in the minor scale in the common practice period of Western music usually uses a leading tone a semitone below the tonic: the chord built on the dominant (fifth scale degree) is almost always a major triad, at least at cadence points; consequently the seventh degree of the scale must be raised with an accidental. Hence music using the "natural" seventh degree, called the subtonic, sounds ancient, folkloric or modal to Western ears.
A B C D E F G# A'
The interval between the sixth and seventh degrees of this scale (in this case F and G sharp) is an augmented second. While some composers, notably Mozart, have used this interval to advantage in melodic composition, other composers, having felt it to be an awkward leap, particularly in vocal music, considered a whole step between these two scale degrees more conducive to smooth melody writing, so either the subtonic seventh was used or the sixth scale degree raised. Traditionally, music theorists have called these two options the ascending melodic (also known as heptatonia seconda) and descending melodic minor scales, the latter being simply the natural minor, the former being identical in its upper tetrachord to the major scale:
A B C D E F# G# A' and then
A G F E D C B A' respectively
Composers have not been consistent in using these in ascent and descent melodies. Just as often, composers choose one form or the other based on whether one of the two notes is part of the most recent chord (the prevailing harmony). Particularly, to use the triad of the relative major - which is very common - since this is based on the third degree of the minor scale, the raised seventh degree would cause an augmented triad; composers thus frequently require the lowered seventh degree, that which is found in the natural minor.
Major and minor keys which share the same signature are called relative; so C major is the relative major of A minor, and C minor is the relative minor of E-flat major. The relative major is a minor third above the tonic of the minor. For example, since the key signature of G major has one sharp (see major scales for how to find this), its relative minor, E minor, also has one sharp in its key signature.
Music may be written in an enharmonic scale (e.g. C-sharp minor, which only has four sharps in its key signature, compared to the theoretical eight flats required for D-flat minor). The following are enharmonic equivalents:
|Key Sig.||Major Scale||Minor Scale|
|5/7||B/C major||g/a minor|
|6/6||F/G major||d/e minor|
|7/5||C/D major||a/b minor|
Double sharps/double flats can be written as accidentals, but not as part of a key signature. For example:
D Minor Key Signature: B + E + A + D + G + C + F + B (the B is now double flatted)
D Natural Minor = D E F G A B C D
D Melodic Minor (Ascending + Descending) = D E F G A B C D C B A G F E D
D Harmonic Minor = D E F G A B C D