From Wikipedia, the free encyclopedia

A minor/major seven chord (alternatively written m/M7, minor major seventh and *lowercase root name*M7, such as am/M7) is a naturally occurring diatonic chord in the harmonic minor scale. The chord is built on a root, and above that the intervals of a minor third, a major third above that note and above that a major third. It can also be viewed as taking a minor triad and adding a major seventh. The traditional numeral notation is based on the degrees of the major scale, and by this notation a minor/major seventh chord is degrees 1, b3, 5, 7 of the major scale.

The chord occurs on the tonic when harmonizing the harmonic minor scale in 7th chords. The harmonic minor scale contains a raised seventh, creating a half step between the seventh and the root. This half step creates a pull to the tonic that is useful in harmonic context and is not present in the natural minor scale (also known as the Aeolian mode). When building a chord on the fifth or the seventh of the minor scale, this raised seventh is present, and so both of these chords have a strong pull to the tonic. However, this same effect makes the tonic seventh highly unstable. The raised seventh in conjunction with the tonic creates the dissonant interval of a minor second. The raised seventh creates a pull towards tonic, however since it is present in the tonic minor chord this pull creates dissonance.

The minor/major seventh chord is most often used in jazz, typically functioning as a minor tonic. Jazz musicians usually improvise over the melodic minor scale on this chord, although the harmonic minor scale is also used.