standards

[wrench45us]

I'm expanding my theory horizons in the Great American Songbook and I'm finding a lot of dim7 and minor flat5 7th chords that either serve sort of as passing chords (with no shared notes -- sort of like a more minor tritone) or with a couple of shared notes as key modulators

quick ex.
Cmaj7 Dm7 C6/E Ebdim7 Dm7 Gsus9 Gm7 C9

that Ebdim is pretty typical twist


from the C9 the tune ('You can't take that away from me') modulates to F#mb57 to bmb9 to em6 -- it's some nice voice leading on the C and E but twists around to another key

Can the resident theorists provide some ways of thinking about these sort of changes?

[DrawMusic]

I think Berklee called these "passing diminished 7ths". In the above case, in the C6/E Ebdim7 Dm7 section, the chromatic motion in individual voices -- g-gb-f and e-eb-d -- plus the fact that the Ebdim7 itself sounds unstable, is enough to explain how it works as a "passing" chord.

[wrench45us]

thanks that response led me to this
for which the example of Two Five of Five is also what I'm seeing

http://www.jacmuse.com/melodic%20resour ... page31.htm

more than enough to keep me busy

[arbogast]

Yep.
I'll more often than not regard the Ebdim followed by Dm7 as a D7b9 (D7alt) without root and voice it like that too, depending on melody of course. Thi line of thought makes it the dominants dominant (sry, dont know the correct english abbr.)

During comping or soloing a nice voicing is LH: Eb, A, D - RH: F#, C, F
(=typical B7#9 + D7#9 voicing)