C Minor 6th
m6
0 - 3 - 7 - 9Minor + major 6th
About C Minor 6th
C minor sixth places an A natural over a C minor triad — C, E♭, G, A — and the result belongs to swing and to minor blues rather than to rock. On guitar it is a barre chord at the third or eighth fret, and its main modern use is not as a minor chord at all.
The notes
C, E♭, G, A. The A is a major sixth above the root, and against the E♭ it produces the characteristic tension of the minor sixth — bright and dark at once.
Read from A the same notes give A half-diminished; over an F bass they give F9. The second equivalence is the one arrangers use: playing Cm6 over F is the standard way to voice a dominant without doubling the root.
On the fretboard
Third fret with the root on the A string, or eighth with the root on the low E. Both are barres; the top strings are often muted, since the chord works better compact than spread.
In gypsy jazz the three-note version played on the middle strings is standard — the idiom values attack over fullness, and the missing notes are supplied by the ensemble.
Where it shows up
As a tonic in C minor in swing, and as a rootless F9 in jazz comping. It also appears in minor blues in C, where it replaces the seventh on the home chord.
Outside those idioms it is rare, and that rarity is informative: the minor sixth belongs to a period of popular music that ended before the electric guitar became dominant.