Augmented sixth

In septimal meantone temperament, it is specifically equivalent to the harmonic seventh (a just interval of 7:4).

Its most common occurrence is built on the lowered submediant of the prevailing key, in which position the interval assumes a natural tendency to resolve by expanding to an octave built on the dominant tonal degree.

It is the strong tendency to resolve in this way that properly identifies this interval as being an augmented sixth rather than its more common enharmonic equivalent: the minor seventh, which has a tendency to resolve inwardly.

As the augmented sixth is correctly named only in certain specific contexts, the notational distinction between it and the minor seventh is often ignored.

The just augmented sixth arises in the extended C major scale between A♭ and F♯.