There are only 3 fully-diminished chords. On C, Db, and D. If you start one on Eb, you’re already playing an inversion of the one on C.

Why is that compelling? Because diminished chords are at the heart of a lot of beautiful music. They are at the heart of dissonance, and dissonance is what makes music compelling.

Two different ways of analyzing: 1) how do diminished chords function? 2) how to get to one of the three dim chords from somewhere?

  1. D minor 7 -> passing Eb dim -> passing

ii -> V7b9

The diminished chord

  • Can be used with any minor chord; often appears in a iii V/iii ii V I turnaround.

I -> II7b9

Think of Take the “A” Train. That second chord, the D7, could be played with a diminished chord that starts on the tonic C and implies the flat 9 of the D7 dominant chord.

  • The I6 chord (C E G A)

From a major chord

I VI7 ii V7 - depending on the root motion, functions as the VI7 dominant to the ii OR as a “passing diminished” from the I to the ii.