Extended chords (or higher numbered chords) have notes in addition to the basic triad. These are called extensions... i.e. 7th, 9th, 11th, 13th.
Here are the basic guidelines regarding extended chords:
There are other guidelines and rules of the road regarding extended chords. Look at the following examples will point out.
This is how a C7 chord stacks up:
There is a C major triad + a 7th (minor 7th)
More chord extensions follow below: the 9th, 11th and 13th.
To get the correct letter name of the chord member, or extension, just count up,line - space - line - etc. till you get to the next extension.
Counting up from the 7th, first extended chord is the 9th. This is how a C9 chord stacks up:
there is a C major triad + a 7th + a 9th (major 9th)...
or, C - E - G - Bb - D
A complete 9th chord has 5 notes. They can be divided with the root in a bass instrument (or left hand) and the other notes inverted in a treble instrument (or right hand).
Note: a 9th is the same as a 2nd, just an 8va higher - so diatonic 2nds & 9ths are major.
Next, counting up from the 9th, we go to the 11th. This is how a C11 chord stacks up:
there is a C major triad + a 7th + a major 9th + a perfect 11th
Note: an 11th is the same as a 4th, just an 8va higher - so diatonic 4ths & 11ths are perfect.
RULE: 11th chords always (well, 99.9% of the time) eliminate the 3rd. The sound of the 3rd would clash very badly with the 11th (try it), so it is left out!
A C11 would be C - G - Bb - D - F
A C11 is sometimes referred to as a Gm7/C.
Counting up stepwise from the 11th, we go to the 13th. This is how a C13 chord stacks up:
there is a C major triad + a 7th + a 9th + an 11th + a perfect 13th
Note: a 13th is the same as a 6th, just an 8va higher - so diatonic 6ths & 13ths are perfect.
RULE: 13th chords usually eliminate the 5th & 11th
A C13 would be C - E - Bb - D - A
A similar version might eliminate the 3rd & 5th like this...
C13(add11) = C - Bb - D - F - A
more commonly referred to as a Bbmaj7/C
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