So far, we have covered triads and 7th chords, which we built from stacking various combinations of thirds. This system of stacking thirds can be extended beyond the 7th and if we follow it to its logical conclusion then we find that the building of a chord takes us through every scale degree in order of odd numbers. The 9th, 11th and 13th are reffered to as extensions and are not often played altogether at once as each note provides its own colour and sound.
In C, these intervals are:
C E G B D F A
1 3 5 7 9 11 13
The 9th, 11th and 13th are compound names for the 2nd, 4th and 6th.
C D E F G A B
1 2 3 4 5 6 7
9 11 13
When we build an extended chord, we use each note in order up to the extension we want.
So a 9th chord would be:
1 3 5 7 9
An 11th chord would be:
1 3 5 7 9 11
And a 13th chord would be:
1 3 5 7 9 11 13
As there are so many variations of extended chords, there is no point at looking through them all at once. An easier way to memorise this is by remembering that the 9th, 11th and 13th are always classed as major or perfect unless indicated otherwise.
A C major 7 chord would be extended with the major 9 (D), the perfect 11th (F), and the major 13th (A).
A C minor chord would use exactly the same extensions of D, F and A, as would a C7, Cm7b5 or C augmented 7th.
We have to change the chord symbol to indicate any alterations that aren’t major or perfect. For example, a b9, #11 or b13 etc. would have to be shown in the chord symbol.
Extensions are built from 7th chords and are named accordingly. The number 7 is changed to the number of the extended chord – a major 7 chord is naturally extended to a major 9, major 11 and then a major 13 chord. A minor 7 is extended to a minor 9, minor 11 and then a minor 13 chord.
Here is the notation for the more common variations of extended chords:
Extensions Practice Routine
Now we’ve covered each extension, we can create an exercise for practising these arpeggios: