Moving beyond 7th chords, we enter the huge, shimmering, full-orchestra sounding world of 9th chords. Simply put, 9th chords are extensions of 7th chords. In fact, there is a corresponding 9th chord for each of the three types of 7th chords:

Cma7     Dmi7     G7
Cma9     Dmi9     G9

Here is the structure for major 9th chords:

1        3     5        7     9
C        E     G        B     D = Cma9
     2     1.5      2      1.5  = Major 9th structure

A brief intro to chord substitution is in order. Notice there are actually three triads contained in this Cmaj9 chord:

C      E      G                = C
       E      G      B         = Emi
              G      B      D  = G

Also notice we can extend the Emi to Emi7:

E      G      B      D = Emi7

It may seem early on to bring chord substitution into our discussion, but I feel it is important for you to begin viewing chords as more than one chord. In the case of this Cmaj9 chord, we really are looking at six different chords!

C    = C E G
Cma7 = C E G B
Cma9 = C E G B D
Emi  =   E G B
Emi7 =   E G B D
G    =     G B D

In practice, when I see a Cmaj9 chord on the music, I may play any of these six chords, depending on the effect I am after. In fact, I never view chords as one chord – and as you will see, I even throw out the concept of major / minor – but we have a ways to go before doing that.

For now, you can easily see for example if you played an Emi7 chord, with the bass player playing a C, we have a beautiful Cmaj9 sound – and in practice it is usually preferable, since doubling the bass can clutter the overall sound of the band.

Now let’s check out the structure for minor 9th chords:

1     3        5     7        9
D     F        A     C        E = Dmi9
  1.5     2       1.5    2      = Minor 9th structure

Can you spot all six chords here?

Dmi  = D F A
Dmi7 = D F A C
Dmi9 = D F A C E
F    =   F A C
Fma7 =   F A C E
Ami  =     A C E

Here’s what happens when extending the dominant 7th to a 9th chord:

1        3     5     7        9
G        B     D     F        A = G9
     2     1.5   1.5     2      = Dominant 9th structure

And here are the six chords within this G9 chord:

G      = G B D
G7     = G B D F
G9     = G B D F A
Bmi-5  =   B D F
Bmi7-5 =   B D F A
Dmi    =     D F A

So, is the G9 a dominant chord? Glad you asked – the answer is yes, since it is simply an extension of the G7 chord, which contains the mi7 interval against a major chord. More importantly, inside all dominant chords is an interval that is not found in major or minor chords: the Tritone.

So, what the heck is a Tritone? As the name suggest, there are three (Tri) whole tones in the Tritone interval. Like P4, P5, and P8, the tritone is a perfect interval – there is no major or minor variant, and the tritone inverts to itself. The tritone interval in dominant chords is the distance from the 3rd to the 7th. Here it is within our G7 chord:

1        3     5     7
G        B     D     F
           1.5   1.5   = Tritone interval, 3 whole tones

This interval only occurs when two minor 3rds are joined together – since a minor 3rd is 1.5 steps, two of them equals 3 whole steps. Consequently, the tritone also occurs in our beloved mi-5 chord. Here it is in Bmi-5 and Bmi7-5:

1        3        5        7
B        D        F
B        D        F        A
     1.5     1.5      2

Since there are 12 half-tones to an octave, which equals 6 whole tones – the tritone interval with its 3 whole tones is exactly the center point of an octave! It produces a sound unlike any other, leaning toward the bluesy / jazzy side, but is found in nearly all forms of music. It is the dominant 7th sound, and is usually the strongest point within compositions – lots of tension that begs to be resolved.

We’ll be spending much more time on the tritone later on. The most important thing for now is to recognize it only occurs in the V and VII chords in every key, and is what distinguishes major 7th or major 9th chords from dominant 7th or 9th chords.

So, what is the difference between a G2 and a G9, since they both contain a A note? The answer is important, since this tends to be another one of those points of confusion, even for some accomplished musicians. Here is it:

The presence of the 7th determines whether a chord is called by its extended name or not. In fact, chord names beyond the 7th unto itself implies the presence of the 7th – i.e ma9, mi9 and 9th chords all imply a 7th is present in the chord.

Notice the difference between a G2 and a G9:

1       3       5       7       2 / 9

G       B       D               A  =  G2

G       B       D       F       A  =  G9

G2 does not contain the 7th, in this case the F note. More importantly, since the 7th (F) is missing, there is no tritone interval in the G2 chord. Remember, in a dominant 7th chord, the distance between the 3rd and 7th is the tritone interval. G2 is a very major, resolved sounding chord – while G9 is a very dominant, unresolved sound – two completely different animals.

So now we are getting into the good stuff! These concepts may seem a bit much, but if you have been following all along, you should really have no problem here. Congratulations, we are smack in the middle of what I would term intermediate chord concepts, and it only gets better from here. In fact, we have just scraped the tip of the proverbial iceberg!

To help let all this “theory” sink in, we will be switching to guitar fingerboard concepts in our next blog, and get some practical application going. As always, please feel free to submit any questions or comments – we’ve covered some pretty intense stuff in a fairly short period of time – so any and all questions are encouraged. Until next time, I remain,

Musically yours,

Al