Cdim

Cdim is C, Eb and Gb, a diminished triad. The shape this page opens on is written x31x12, lowest string first.

Note by note. C is the root, Eb is the minor third and Gb is the flat fifth.

Also written C°, Co or C diminished. The same chord either way; which spelling you meet depends on who wrote the chart.

There are 5 common shapes for Cdim on the guitar, and 46 derived voicings in the triad family.

One note away. Change a single note of Cdim and you have Cm (with one note moved), Cdim7 (with one note added), Cm7b5 (with one note added) or CmMaj7b5 (with one note added).

In which keys. Every note of Cdim belongs to C# major (the vii°) and Bb minor (the ii°).

The common shapes, written lowest string first: x31x12, x3454x, 86x87x, x-x-10-11-x-11, x-15-13-x-13-14.

Under the hand. None of the shapes for Cdim uses an open string, so every one of them is movable; the lowest sits at the 1st fret. None of them needs a barre. Together they cover the neck from the 1st fret to the 15th.

Triad. Three notes across one string set. Cdim has 231xxx, x3454x, x645xx, xx454x, x6454x, xxx878, x-9-10-8-x-x, 8-9-10-8-x-x.

Tensions. A shell of Cdim, root, third and seventh, leaves a string free, and the tones that belong over it are the 11 (F) and the b13 (Ab).

What kind of chord this is. Cdim is a diminished chord — root, minor third, flat fifth. diminished and half-diminished chords on every root, and what they are for.

The common shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.