Let's begin by taking a look at a simple, basic G7 (Dominant Seventh) chord:

The 4 chord-tones are: G, B, D, and F which are respectively the Root, the M3, the P5, and the m7.

If we remove the G Root, we will notice that the 3 remaining notes (B, D, and F) actually spell out a B Diminished triad.

Did you know that there was a diminished triad hidden inside a basic Dominant chord ? Not sure ? Well, most people don't, but now you do !

(Note that the Diminished triad is composed of 3 consecutive minor 3rds)

We could now expand our B diminished triad and stack up another m3 on top of it: this extra note (Ab) will make it a B diminished 7th chord: B, D, F, and Ab.

It is very common to use this chord in place of a G7. The resulting sound will be a G7(b9)

We will notice 2 things:

   1. analyzed over G7, the 4 notes of Bdim7 are now: the M3, the P5, the m7, and the b9.

   2. even though we are thinking G7(b9) there is no G root in the chord.

Here comes the fun part: remember that the Bdim7 chord is basically 4 stacked-up minor 3rds. Those 4 notes are equi-distant, which means that the chord is completely symmetrical: any one of the 4 notes can be the root of a diminished chord.

Bdim7:     B,   D,   F,   Ab

Ddim7:        D,   F,   Ab,   B

Fdim7:           F,   Ab,   B,   D

Abdim:              Ab,  B,  D,  F

Therefore, Bdim7 = Ddim7 = Fdim7 = Abdim7

There's no real rule as to which note we should call the root of a diminished chord, but it is generally simpler to assume that the lowest note will give its name to the chord.

Here is how we can quickly figure out which diminished chord we may use as substitution over a dominant chord:

Think up a 1/2 step from the Root of the Dominant.

for G7, think Abdim7

for C7, think Dbdim7

(We could also think of building the diminished chord from the M3, the P5, or the m7 of the dominant).

Let's take a look at some examples illustrating the use of the diminished chord:

ex.1: Here is a simple way to make use of the diminished substitution over a ii-V-I progression:

for Dm7 | G7 | CMaj7

we may think: Dm7 | Ddim7 | CMaj7

ex.2: In a Jazz Blues progression, a #ivdim7 generally follows the IV7 (measure 6).

For Blues in F, we will find Bdim7 right after Bb7 instead of staying on the Bb7 for 2 measures. Now we know that Bdim7 is essentially the same chord as Bb7(b9). We are not changing very much harmonically by using a diminished #iv chord here, but it creates a desirable forward movement, especially if we keep moving up chromatically to F7/C (the I7 chord with the 5th in the bass).

ex.3: Here is another example over a basic I - VI - ii - V turnaround:

for CMaj | A7 | Dm7 | G7 |

we may think: CMaj7 | C#dim7 | Dm7 | Ddim7

The same effect is used at the very beginning of "Have You Met Miss Jones" in the key of F:

FMaj7 | F#dim7 | Gm7 | C7 |

ex.4: Here is another way to treat the same I - VI - ii - V turnaround in C:

C/E Ebdim7 | Dm7 G7 |

In this case, the I chord with the 3rd in the bass (notated C/E) is used instead of the iii7 (which would have been Em7). The Ebdim7 connects chromatically with the Dm7.

The same idea is found in measures 9 through 12 of "All Of You" (key of Eb):

EbMa7/G | Gbm7 | Fm7 | Bb7 |

ex.5: For iii7 - VI7 - ii7 - V7 we can substitute: iii7 - biiidim7 - ii7 - V7

See the final turnaround from "Out Of Nowhere": Bm7 Bbdim7 | Am7 D7 | GMaj7 |

or the last 6 measures of "All The Things You Are": Cm7 | Bdim7 | Bbm7 | Eb7 | AbMaj7 |

in "Chelsea Bridge" (in the bridge section-- no pun intended...)

and in "Night & Day" (measures 11 through 14)

ex.6: Here is another example smoothing out the I - ii - iii progression:

for BbMaj7 | Cm7 | Dm7

we may think: BbMaj7 Bdim7 | Cm7 C#dim7 | Dm7

This is the beginning of a typical "Rhythm Changes" tune such as "Oleo" or "Anthropology". The same progression is used in the opening chords of "Easy Living" (in the key of F) and in "Bewitched" (key of C).

Another variation of the I - ii - iii chord progression is found at the beginning of "Don't Get Around much Anymore" by Duke Ellington:

CMaj7 Dm7 D#dim7 | C/E

Here again, the "destination" I chord with the 3rd in the bass (notated C/E) is preferred instead of the iii7 (which would have been Em7).

The same type of progression is often used as a filler in the tune "Satin Doll" (also by Duke Ellington). On measures 3 and 4 of the bridge, where most lead sheets simply indicate an FMaj7 chord, we can play:

FMaj7 Gm7 | G#dim7 F/A |

ex.7: in "Like Someone In Love", we find an F#dim7 on measure 28 (right before the final iii - VI - ii - V - I). Here again we are approaching the iii7 chord (Gm7) with a 1/2 step from below. We can call this chord #iidim7. In fact, I usually play 2 beats of F#m7(b5) and then 2 beats of F#dim7 in that measure (hence implying F#m7(b5) to B7).

The same diminished chord is found in the exact same place (measure 28) on "Donna Lee" by Charlie Parker: the Bdim7 is also the #iidim7 and its function is now to connect the Bb7 to the Cm7.

Brazilian music is full of diminished 7th chords. You may want to take a closer look at tunes like "How Insensitive", "Corcovado", or "Wave" (all written by Antonio Carlos Jobim) for some great uses of the diminished chord !

ex.8: One clever little device is found in a couple of those Jobim tunes: the i diminished chord (idim7) immediately preceding the IMaj7.

see "Chega de Saudade": Em7 | A7 | Ddim7 | DMaj7 (measures 37 through 40)

or "Corcovado": Fdim7 preceding FMaj

The same trick is used at the very beginning of "Spring is Here": Abdim7 resolving to AbMaj7.

You may want to use the concept in reverse: when improvising over a ii-V7-I progression, you can try to superimpose a idim7 arpeggio while landing on the IMaj7 chord, and then eventually resolve with one (or more) of the chord tones.

So, to summarize everything, let's say that the diminished chord is generally used as a excellent CONNECTOR. Diminished substitutions are an effective way to smooth out chord progressions, and a nice alternative to more predictable root movements in 4ths.

Let's finish this discussion of the diminished chord by admiring this fine example of a smooth descending chord progression, found in the bridge of "April In Paris":

F#m7(b5) Fdim7 | C/E Ebdim7 | Dm7(b5) | C/E |



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