Dim chords

"Dim" stands for diminished and what happens in these chords is that all tones besides the root are flattened. There are both the diminished triads, the diminished seventh and the half-diminished seventh. In the triad, the third and fifth tones are flattened one semi-step. In the diminished seventh (dim7), a minor third is added to the dim triad. Dim chords are quite uncommon and are mainly used for a transition between two chords that don't have an obvious connection.

See diagrams of dim chords:

C dim D dim E dim F dim G dim A dim B dim

C dim7 D dim7 E dim7 F dim7 G dim7 A dim7 B dim7

C half-dim7 D half-dim7 E half-dim7 F half-dim7 G half-dim7 A half-dim7 B half-dim7

Theory

Besides the already mentioned categories, you should know that there is also the half-diminished seventh chord. This chord is identical to the diminished seventh except for the seventh note that is flat instead for double flat (it could also be seen as a minor seventh with a lowered fifth). The half-diminished is more commonly written as m7b5.

Comparing the C Major Chord with different diminished chords:

C: C – E – G
Cdim: C – Eb – Gb
Cdim7: C – Eb – Gb – A (Bbb)
C half-diminished 7: C – Eb – Gb – Bb

The reason for the the B double flat (Bbb) in Cdim7 is because of that the last tone is theoretically a major sixth.

Formula and steps

The formula for the dim triad chord is 1 - b3 - b5. There is three half steps to the 2nd note and three half steps to the 3rd.

Alternative chord symbols

Besides the dim chord symbol that is presented above, you may also find the alternative degree symbol (°), as in , being used occasionally. Half-diminished seventh chord could also be written with a symbol (ø), as in Cø.