Today we will learn about 9th chords. A 9th chord is created when we include a 9th to a 7th chord. If you’re new to building 7th chords, I strongly recommend you to check our previous lesson about it.
The basic idea is that any chord is built by adding intervals to a root note. For example, a major chord (or triad) is a 3-note chord, where we add a major 3rd and a perfect 5th to a root note. So, a C major chord, for example, is made of C, E and G notes. C is the root, E is the major 3rd, and G is the perfect 5th.
To build a minor chord (or a minor triad) we just switch the major 3rd for the minor 3rd:
Seventh chords follow the same idea: we add a note which makes a 7th interval with the root note. In the example below, there’s a Cmaj7 chord:
Notice that we create chords by simply adding thirds to a specific root note.
Now, what would happen if we add one more third to the example above? We would have a 9th chord!
The new chord is a Cmaj7/9 chord. In this example, D is the major 9th.
Simple and Compound Intervals
Simple intervals are not bigger than an octave, while compound intervals are larger than an octave. So, while a 7th interval is a simple one, a 9th interval is a compound one. We can also say that a 9th interval is a compound 2nd interval.
As we seen in the lessons about intervals, there are major and minor seconds, so we can also have major and minor ninths (actually, there are more types of 2nd intervals, but we will cover that in a future lesson).
So, the easiest way to work with a major 9th is to see it as a major 2nd.
With all that said, let’s learn how to quickly build any 9th chord. No matter what chord type we are dealing with, whenever you see a number 9 on the chord, all you need to do is to add a major 9th to it. For example, let’s check a few C chord types:
Dominant Seventh Chord (C79):
The chord formula is: root – 3 – 5 – m7 – 9.
Minor Seventh Chord (Cm79):
The chord formula is: root – m3 – 5 – m7 – 9
Major Seventh Chord (Cmaj79):
The chord formula is: root – 3 – 5 – 7 – 9.
Minor Major Seventh Chord (Cmmaj79):
The chord formula is: root – m3 – 5 – 7 – 9.
Notice that in all examples, we just add a D note (major 9th), which is actually the C major 2nd.
The Add 9th chord
There’s another type of 9th chord, which is widely used in pop music, which is the Add 9th chord. It consists only of a triad plus the 9th (there will be no 7th in this chord).
This chord can also be referred to as ‘added 2nd’.
That’s it! In the next lesson, we will learn about chord voicing.