Diminished chords · Music theory
A symmetrical chord with four names and three distinct sounds; its uses as an ascending or descending passing chord, and as an auxiliary.
Four names, three sounds
The diminished seventh chord is built from three minor thirds, and the fourth distance, from its seventh to the octave of the root, is enharmonically another minor third. It splits the octave into four equal parts. Any of its notes can be the root, because the inversion sounds the same.
So there are only three distinct diminished chords: those starting on C, on C♯ and on D. The one on E♭ sounds like the one on C, and the one on E like the one on C♯. The root you write depends on where it goes.