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Section 18.4 Writing Secondary Diminished Chords

To write a secondary diminished chord, use the following procedure.
  1. First determine the note that is the root of the chord being tonicized (the chord to the right of the slash).
  2. Determine \(\left.\text{vii}^{\circ}{}^{7}\right.\) in the key of C minor (C is the root of the \(\left.\text{iv}\right.\) chord, which is the Roman numeral after the slash): B is the root of \(\left.\text{vii}^{\circ}{}^{7}\right.\) in C minor because it is a m2 below C.
  3. Build a fully–diminished seventh chord on B: B–D–F–A
  4. Invert the chord accordingly. \(\left.\text{}^{4}_{2}\right.\) inversion means the 7th of the chord (A♭) is the bass note.