Quote:
Originally Posted by El Conquistador
I often use (what I call) a passing chord from A to wherever.
I go from A (X02220) to ? (X12020). What is this chord?
Steve
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As mentioned, it's where it's going that could determine the best name for the chord.
It's certainly a dim7 of some kind, and could be named after any of its notes (with some enharmonic flexibility too).
As jerry says,if it's heading for a B-root chord (B major, Bm, B7), then the theoretically correct name is A#dim7, because A#dim7 is the vii chord from B (harmonic) minor. So it naturally resolves to Bm,and can be borrowed to resolve to B major. The notes (stacked in 3rds on the root) are A# C# E G, and A#-G is the defining "diminished 7th" interval (half-step less than a minor 7th).
Given that you're starting from A, that's the most likely identity of the chord.
But as it's a symmetrical chord, it can go three other ways, acting as vii to three other chords (again, major or minor in each case).
As C#dim7 (C#-E-G-Bb), it will go to Dm, D or D7 (that could also be a likely scenario starting from A);
As Edim7 (E-G-Bb-Db), it will go to Fm, F or F7;
As Gdim7 (G-Bb-Db-Fb), it will go to Abm, Ab or Ab7 (and if you call Abm G#m, then the dim7 is Fxdim7: Fx-A#-C#-E, strictly speaking).
Those all apply whichever note is in the bass. E.g, even if Bb is in the bass, if the chord goes to Dm it's C#dim7 (and the bass
would then be Bb, not A#).
Still, this is only about theoretical correctness (proper enharmonic spelling for a vii chord)! In practice, it's normally sensible to call a dim7 after its bass note, not its functional root note.