Cdim7 adds Bbb♭♭7 to . Its four notes, C, Eb, Gb and Bbb, divide the octave into equal minor thirds.
Move the shape three frets and it repeats the same pitches under a new root name. That symmetry helps it connect steadier chords from several directions.
Also written C°7, Co7 or C diminished 7.
Cdim7 shares its root with C and slips in between F and the I. It isn’t a new harmony, only decoration: two notes hold, and the rest move by step into the home chord.
Listen for: The IV’s root rises a half step, then another, into the fifth of the I, over a bass that never moves.
Heard in“True Love”“Calendar Girl”“Daydream”
Cdim7 is the dominant seventh flat nine of the chord a half step above it, with the root left out. Any of its four notes can be the one that rises, so it can lead into four chords; between Bmaj7 and C#m7 it walks the bass up by half steps.
Listen for: The bass climbs a half step at a time, from the root of the I to the root of the ii.
Cdim7 occurs naturally in C♯ minor: the harmonic minor scale builds it on the leading tone, a half step below C#m.
Played after Cmaj7, Cdim7 can lead into Dbmaj7, and so into a new key a half step up. Since any of its notes can act as the leading tone, one diminished chord can lead into four keys.
Alternating Db6 and Cdim7 is the sixth–diminished sound: the diminished chord is the V7♭9 of Db6 with its root left out.
Contains Cdim7 and adds second, fourth, sharp fifth and major seventh.
Contains Cdim7 and adds flat second, major third, fifth and flat seventh.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.