The previous chord theory post looked at extending chords past the seventh by adding ‘tensions’. Tensions are the more ‘colourful’ notes of the chord and add interest to the basic chord’s sound. Adding tensions to triads is a way of adding more colour to triads, without needing to include the seventh.
A major sixth chord is a major triad with a major sixth added on top. The formula for a sixth chord is therefore 1, 3, 5, 6. For a C6 this would mean adding an ‘A’ to the Cmaj triad which would give C, E, G, A.
Maj6th or Min7th?
Sixth chords are interesting in that they contain the same notes as a major seventh chord, but taking a different note as the root. In the case of a C6 chord, the C, E, G and A could be rearranged into thirds, with the A on the bottom. This gives us A, C, E, G which is an Amin7 chord.
For this reason some people prefer to think of sixth chords simply as inversions of major seventh chords (inverting a chord simply means that the lowest note is not the root – more on that in a coming post). So a C6 can be thought of as an inverted Amin7.
Minor 6th Chords
A minor sixth chord is a minor triad with a major sixth added on top. The formula is therefore 1, b3, 5, 6 so a Cmin6 would be C, Eb, G, A.
Just as the C6 is an inverted Amin7, a Cmin6 is an inverted A half-diminished chord.
Add9 and Min Add9 Chords
Adding the major ninth to a major chord creates an add9 chord. The add9 chord formula is therefore 1, 3, 5, 9 which can also be thought of as a regular maj9 or dominant 9 chord with the seventh left out.
Adding a major ninth to a minor chord formula gives the madd9 formula: 1, b3, 5, 9. This is the same as a min9 chord but with the seventh omitted. Madd9 chords can be safely used in place of min9 chords when a simpler, ‘leaner’ chord voicing is required.
69 and Min69 Chords
The sixth and the ninth are two of the ‘prettiest’ chord tones in any chord – they are colourful without being dissonant. By adding both of these notes to a basic major triad, we are able to arrive at full, ‘fleshed out’ chord voicings, without the dissonance that could occur if we included the major seventh. The chord formula for a maj69 chord is therefore: 1, 3, 5, 6, 9.
In minor-key jazz tunes, min69 chords are also a great chord to use on the tonic minor. They are more colourful than the tonic min6, but not as strident as the min/maj7.