Of course, we know that Adim7, Cdim7, E♭dim7, and G♭dim7 use the same notes, so they’re completely interchangable. F7♭9 would use the G♭dim7 chord substitution.D7♭9 would use the E♭dim7 chord substitution.B7♭9 would use the Cdim7 chord substitution.A♭7♭9 would use the Adim7 chord substitution.It works every time due to the symmetry of the dim7 chord. The easiest way to learn this substitution is to take the root note of the 7♭9 chord, raise it by a semitone (1/2 step) and play that diminished chord.
D is a major third down from G♭, therefore you can substitute for D7♭9.B is a major third down from E♭, therefore you can substitute for B7♭9.A♭ is a major third (2 steps) down from C, therefore we can substitute for A♭7♭9.This means that you can find a root note by going down a major third from any note. Consider that we know the diminished 7 chord voicings are interchangable. If you add a root note, which is usually played by a bass player, you have a 7♭9 chord.
Those are the same intervals as the dim7 chord. Actually, diminished 7 chords substitute for four different 7♭9 chords. Diminished chord theory is a topic worthy of its own lesson (or course), but I will try to explain one of the primary uses in Jazz, which is as a chord substitution.ĭiminished 7 chords are used as chord substitutions for Dominant7♭9 chords. If they are, it is based on the 7th degree of the scale. They can be used in a major key, but this is not common. Diminished chords are not used very often.