> But it
> doesn't really explain why II-ii wants the #11.
Well, this is kind of nice little tie-in to the George Russell thread,
but I think (as an earlier post pointed out re. Russell) that all
dominant chords "want" the #11. If you look at the overtone series of
any fundamental pitch, the seventh overtone (counting the fundamental as
1) is a flat seventh, and the eleventh overtone is a sharp 11.
This is one area of music theory where brass players are at an
advantage, since we deal with upper-partial overtones all the time.
Here's the overtone series based on Bb:
1 2 3 4 5 6 7 8 8 10 11 12 ...
Bb Bb F Bb D F Ab Bb C D E F ...
which spells out a rather awkwardly voiced Bb7#11. As you can see, the
fact the 7th and 11th of the chord correspond to the 7th and 11th
overtones is just a confusing coincidence.
The 7th and 11th partials are about a quarter-tone flat, which is why a
flat b7 sounds more consonant than one that's "in tune." And why "blues
sevenths" in non-fixed-pitch instruments tend to flatten--even to slide
almost to the 6th.
In piano-less settings, you can exploit the overtone series by
flattening notes in the upper register, which in combination with the
bass, create these passing "consonances" that don't exist in equal
temperament. It's a nice (and easy) way to use microtonality in jazz.
(The bass player can do the same by raising notes at the bottom.) But I
digress...
Howard