Minor sixth
Eight semitones, the inversion of the major third.
What it means
The minor sixth comprises eight semitones and arises through inversion of the major third: if one places the lower note of a major third an octave higher, a minor sixth results. Like the major sixth it counts as an imperfect consonance and may be led in parallel.
Musical use
In the first-inversion chord of a minor triad, the minor third and the major sixth stand above the bass; in the first-inversion chord of a major triad, by contrast, the minor sixth stands above the third in the bass. Whoever wants to determine the sonority must therefore check both — the sixth alone does not yet say which mode is present.
In sound the minor sixth is soft and somewhat veiled; it counts as the more expressive of the two sixth intervals and appears in melodic use often at places of particular intimacy. Leapt upward it often leads to a peak note from which the line goes back stepwise.
In minor it arises between the root and the sixth degree; the question whether this degree is raised distinguishes natural, harmonic, and melodic minor and changes the character of the scale.
It is to be distinguished from the augmented fifth: both sound the same on tempered instruments, but the augmented fifth belongs to the augmented triad and strives apart, while the minor sixth is a consonant interval.
The minor sixth counts as an imperfect consonance and is perceived in minor as a mark of the sixth degree. In major it appears, for instance, between the third and the upper root. A melodic leap of a minor sixth often seems full of longing and is used in vocal music as a means of expression; if the voice then falls back stepwise, a typical sighing line arises.
Performance practice
Sing the minor sixth by way of its inversion if the leap is hard: thought as a major third downward. Intonate it rather close, just as the major third acts wide — both follow the same acoustic reason. And lead the line back after a leap of a sixth so that the phrase stays in balance.