6. Extended chords
As we mentioned, seventh chords “extend” intervals beyond the fundamental ones found in triads. But extensions are not limited to sevenths. We can add any degree of the scale on top of triads and sevenths to create further chord extensions.
We don’t usually refer to chords as “major second” chords or “minor fourth” chords. Because these chords are “extending” past the initial octave of the scale we’re in, we add 7 to the degree of the scale that we include in the chord (7 because that is the number of notes in a standard scale).
If we include the second degree in the chord, we call it a “ninth” (2+7).
If we include the fourth degree, we call it an “eleventh” (4+7).
And if a sixth degree is present, we call it a “thirteenth” (6+7).
There are too many types of extended chords to list here. But chord extensions add color and variety to chords.
Here is a minor 9 chord, made up of a root note, minor third, perfect fifth, minor seventh, and major nine (the major second interval from the root note, but voiced up one octave):