The minor sixth on 7-string guitar

A minor sixth is eight semitones, from C to A♭. Inverted, with the lower note moved up an octave, it becomes the major third.

Its short name is m6. Counted in letters, it spans six letter names, which is why it is written C to A♭ rather than with another name for the same pitch.

On 7-string guitar, the minor sixth is three frets up and four frets up when you cross to the next string, and eight frets up along one string.

One pair of strings is the odd one out, because the gap between those two strings is different from the rest. Most players learn that exception as a rule of its own.

On a treble staff, the two notes are written C and A♭.

The staff shows the two notes one after the other, then together. C to A♭ spans six letter names, which is what the interval's name counts. What you hear is a distance of eight semitones.

A keyboard makes this distance easy to see, where a fretboard hides it. The upper note is eight keys along from the lower one, counting black and white keys alike.

28 notes are marked across seven strings.

This diagram marks both notes of the minor sixth, C and A♭, everywhere they fall on 7-string guitar. You can find every pair shown above somewhere on it.

C–A♭, D♭–B𝄫, D–B♭, E♭–C♭, E–C, F–D♭, F♯–D, G–E♭, A♭–F♭, A–F, B♭–G♭, B–G

The shapes above do not change with the key, which is the reason to learn an interval as a shape. Only the note names change, and this table gives them for every starting note.

Two chord types contain a minor sixth: Augmented, Augmented major 7th.

These are the chords with a minor sixth above their root. Some of them spell that note under another name, but it is the same distance and the same shape on the neck. A chord is built by stacking intervals on a root, and a triad is the simplest case, with two of them.