Diminished 7 Substitution For Dominant 7 Chord For Guitar

A dominant 7th chord (V7) can often be substituted or reinterpreted as a diminished 7th chord built on certain chord tones.

This works because of the shared tritone (the 3rd and 7th of the dominant chord), which defines the chord’s tension and resolution.

Build the diminished from the 3rd of B♭7

B♭7 = B♭–D–F–A♭

The 3rd is D

Build a diminished 7th chord on D:
→ D°7 = D–F–A♭–C♭ (B)

Now, look at the relationship:

B♭7(b9) = D°7 – D being the 3rd of B♭, A♭ the ♭7, B (C♭) the ♭9 and F the 5.

So whenever you see B♭7, you can substitute D°7, and it will sound like B♭7(b9) — a more colorful, tension-filled version of the dominant.

Because diminished 7 chords are symmetrical, Ddim7 provides three other dim7 chords.

Bdim7, A♭dim7 and Fdim7.