Diminished 7th's
Where do they go?
Ah, the weird anomaly of the diminished 7th chord. Not really a chord you would use to start or stop a song - as it is transitional by nature. Every type of diminished chord, (the diminished, half-diminished and the diminished seventh), all need to be placed in context to the chord progression for it to make melodic sense to the listener.
What is the diminished chord?
Think of the basic diminished “triad” as a minor chord with a flatted 5th (b5):
C° = C - Eb - Gb
The structure of the diminished 7th chord.
Music mathematical anomaly indeed!
The “diminished 7th” adds one more note to the triad. This note is the “double-flatted 7th”:
C°7 = C - Eb - Gb - Bbb (A)
The entire °7 chord structure is based on “minor 3rd” intervals. Each of the notes in a °7 is the “root” note.
Weird, huh?
As you can see in this graph, the C°7 notes are: C - Eb - Gb and Bbb (A). Each note is a “root” note, as the structure is repeated in minor 3rds.
By the way - Yes, we will be referring to the (A) note as “Bbb”. Why? Because it is to be understood as a “double-flatted 7th” interval, and not necessarily a Major 6th interval…at least, for this lesson.
Clear as mud?
Where do diminished chords go in a chord progression?
If you know your keys and the circle of fifths, you know that each chord in every key has its own Roman numerical interval value:
If we turn these intervals into chords, they look like this:
Diminished 7th’s go here!
It is generally understood in basic music that diminished chords can be used as chromatic transitional chords in any empty space between these seven chords:
Here is how Google A.I explains it:
What does all of this look like on the fretboard?
(Substitute "Bbb” with the “A” for this exercise for easier reference.)
There are literally two shapes that are used primarily as diminished 7th chords on the guitar.
Using strings 4 -3 -2 -1
Using strings 5 - 4 - 3 - 2
Because each note in both shapes can be thought of as the “root” note; and because of the standard tuning of the guitar, both shapes are seen as “static” in structure, and can be moved to four different places, every three frets.
To find the other eight diminished 7th chords, all you need to do is move up one fret or down one fret.
For more on how you can practice and utilize these weird chords in music, check out this article I posted last November.