Diminished Seventh Chords - Theory

Diminished seventh chords are very useful in jazz.  They add a bit of tension to a chord progression and resolve nicely to the next chord.

Diminished seventh chords are made up of 4 tones, the root, flatted 3rd, flatted 5th and doubled flatted 7th of the major scale.

Let's build a CDim7 chord.  Here's a C major scale:

root  C
2      D
3      E
4      F
5      G
6      A
7      B

So, a CDim7 chord would consist of C Eb Gb Bbb. Bbb is the same tone as A.

There are a couple of ways I look at a diminished seventh chord.

A diminished seventh chord is a dominant seventh chord with the 3rd, fifth and flat 7th all flatted.  Thus the Bbb.

My favorite way to think about a diminished seventh chord is to take a dominant seventh chord and sharp the root.

C Dominant Seventh     = C E G Bb
C# Diminished Seventh = C# E G Bb

Let's look at the intervals between the tones of a diminished 7th chord.

On the guitar an interval of a half step is is one fret difference between two tones.

root - flatted 3rd = 3 half steps = minor 3rd

flatted 3rd - flatted 5th = 3 half steps = minor 3rd

flatted 5th - double flatted 7th = 3 half steps = minor 3rd

double flatted 5th - root = 3 half steps (frets) = minor 3rd

Since the intervals between tones are all 3 half steps, any tone in the chord can be its name!

CDim7   = C Eb Gb Bbb (Bbb = A)
EbDim7 = Eb Gb Bbb Dbb  (Dbb = C)
GbDim7 = Gb Bbb Dbb Fbb (Fbb = Eb)
ADim7    = A C Eb Gb

6th and Minor 7th Chords

To build an F6 chord start with an F major scale and select the 1st tone (also known as the root), 3rd tone, 5th tone and 6th tone.

Here are the tones in an F major scale:

root   F
2       G
3       A
4       Bb
5       C
6       D
7       E

The tones in an F6 chord are F A C D.

To build a DMin7 chord start with a D major scale and select the 1st tone, flatted 3rd tone, 5th tone and flatted 7th tone.

Here are the tones in a D major scale:

root   D
2       E
3       F#
4       G
5       A
6       B
7       C#

The tones in a DMin7 chord are D F A C. Notice that we had to flat the 3rd (F#) and 7th (C#) tones.

So we find that the tones in an F6 and DMin7 are the same! You can use the same fingering for both sixth and minor seventh chords.

I differentiate between sixth and minor seventh chords based on the tone a bass player would probably play along with each chord.

If the progression calls for an F6 chord, a bass player would play an F tone.

If the progression calls for a DMin7 chord, a bass player would play a D tone. 

F Major Jazz Chord Progression #1 on Strings 1 - 4

Here's a jazz chord progression I like:

F6 /  F#Dim7 /  GMin7 /  C7b9 /  F6

Here's what it sounds like:

Here are the chord diagrams:
 
F6 means F sixth.
F#Dim7 means F# diminished seventh.
GMin7 means G minor seventh.
C7b9  means C seventh flat ninth.

This is a variation of the ii - V - I chord progression.

I (roman numeral for one in upper case letters) represents the major chord based on the first tone of the major scale.

ii (roman numeral for two in lower case letters) represents the minor chord based on the second tone of the major scale.

V (roman numeral for five in upper case letters) represents the major chord based on the fifth tone of the major scale.

In the key of F, F major is the "I" chord, G minor is the "ii" chord and C major is the "V" chord.

It is very common to make the V chord a dominant seventh chord.

In the chord progression at the top of this post I substituted F sixth for F major, G minor seventh for G minor and C seventh flat ninth (no root) for C dominant seventh.

I added a F# diminished seventh chord between the I and ii chords. Diminished seventh chords can sometimes be used in transitions between chords.

You probably noticed that the 7b9 (no root) chord looks like the dim7 chord at a different fret. These two chords share the same tones.

I'll be writing more about how these chords are formed in upcoming posts.

Welcome to my blog!

Welcome to my blog.  I teach guitar, mandolin, banjo (5 string, tenor & plectrum) and ukulele in Plano, Texas in my home near Coit and Hedgcoxe.

I will be posting information here that I hope will help you be a better guitar player.

Feel free to contact me at lewisjd@gmail.com with any questions, suggestions or corrections to any of the material I post.