The dim (diminished) chords are quite uncommon, but it is still good to be familiar with this chord category. If you play a dim chord you will hear that these chords lack harmony and this is because of the structure of the notes.
A common function for these chords is to be used as a chromatic transposition chord, like an in-between chord, also called a passing chord – this is most common in jazz. If you are interested in the theory, the dim chord consists of a flatten third and a fifth besides the root. If we compare the structure of a C major and a Cdim the notes are C - E - G (C major) and C - Eb - Gb (Cdim). A diminished chord can be written with an abbreviation "dim" (Cdim) or a symbol "º" (Cº).
The easiest way to learn dim chords is to memorize two movable shapes. Below you can see the shapes for dim and dim7. The lowest note is the root (see list below for full overview).
All diminished and diminished 7th chords with same movable shapes listed and written in short notation. Two different shapes are in some cases presented for the dim triads, which both have similar bass and root notes. Notice that for the dim7 shapes, the bass note isn't always the root.
Cdim - X3454X
C# / Dbdim - X4565X
Ddim - X5676X
D# / Ebdim - X6787X
Edim - X7898X
Fdim - X 8 9 10 9 X / 1231XX
F# / Gbdim - X 9 10 11 10 X / 2342XX
Gdim - X 10 11 12 11 X / 3453XX
G# / Abdim - 4564XX
Adim - 5675XX
A# / Bbdim - 6786XX
Bdim - X2343X
Cdim7 - X X 10 11 10 11
C# / Dbdim7 - XX2323
Ddim7 - XX0101
D# / Ebdim7 - XX1212
Edim7 - XX2323
Fdim7 - XX3434 / 123131
F# / Gbdim7 - XX4545
Gdim7 - XX5656 / 345353
G# / Abdim7 - XX6767
Adim7 - XX7878 / 567575
A# / Bbdim7 - XX8989
Bdim7 - X X 9 10 9 10 / 789797
Notice that the root note is the same as the bass note for all diminished 7th versions.
A chord progression including this dim chord shape:
D - D#dim7 (XX1212) - Em (XX2000)
The dim triad is built with the formula 1-b3-b5. The dim 7th is built with the formula 1-b3-b5-bb7.
Notice that the dim7 chords are symmetrical. All inversions of the chord can be played with the same shape. This can be seen by comparing the following diagrams:
Dim7 chords with identical notes
This circumstance results also in that many dim7 chords share the exact same notes (so-called enharmonic chords). For example, Adim7 will use the same notes as Cdim/A, A#dim7 will use the same notes as C#dim/Bb and so on. Below is a larger comparison of this with names and short notation:
Ddim7 = Fdim7/D = Abdim7/D = Bdim7/D - XX01010
Edim7 = Gdim7/E = Bbdim7/E = C#dim7/E - XX2323
Fdim7 = Abdim7/F = Bdim7/F = Ddim7/F - XX3434
Gdim7 = Bbdim7/G = C#dim7/G = Edim7/G - XX5656
Adim7 = Cdim7/A = D#dim7/A = F#dim7/A - XX7878
Dim7 chords (closed and open positions)
None for the moment in this category
Concerning the "non-movable" open and closed dim chords, in some cases an alternative bass note is used for making the chords easier to play. The diagram that shows Cdim7 is more correctly written as Cdim7/Eb. The diagram that shows Edim includes a Db note, which is not fully correct, but is a practical solution in this case.
More dim chords in open positions.
A#dim / Bbdim - X1X020
More dim7 chords with movable shapes.
With root note on the 6th string:
Adim7 - 5 X454X
With root note on the 5th string:
Ddim7 - X5656X
Chord progressions with dim chords
The typical function of a dim chord in sequences is as a chromatic passing chord:
Cmaj7 - C#dim7 - Dm7 - G7
F#7 (XX4320) - Edim7 - Dmaj7
F (133211) - G (355433) - G#dim (4564XX - Am (577555)
Here are other progressions:
Gm - Edim7 - F
Gm - Cm - D - Gm - Cdim - Gm
Ab - Dbm - Adim
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