Classical musicians usually know practically nothing about jazz theory. When they do, they tend to throw a wet blanket over it and send it through some sort of blender: a violins and trap-set Osterizer. I might have done this inadvertantly myself, by ear.
I am very close to an excellent jazz pianist and theater organist, who plays no matter what. Unstoppable. Can't shut him up at the keyboard. He hears music, as he hears paranoid voices. That might lend a clue as to why I care. Music saves his sanity as it enlightens my sanity.
I've loved jazz all my life, but loved classical music just a little bit more, so I went classical. In truth though, jazz musicians enjoy life more on the whole, and are often a hell of a good time. Contrast that to being in a room full of professional organists - each hating one another's playing secretly or not for some very tiny reason. Solo out a fugue subject in Bach on the clarinet stop and end up in organist-hell.
There are marvelous attempts, most made before 1970 at bringing jazz and classical music together, in the serious concert hall. I'm not talking about Ives. There is no reason each type of music needs to sacrifice it's sense of being. That is, jazz unadulterated should be able to be in the same room with classical (ibidem), and things can still go smoothly.
For the composer, this is a serious matter. If I write chords that I actually asked for from my jazzer friend, or lifted from some pop chart sound I heard in my youth, it gets labelled "French" by the classical people.
This is not unrealistic: for I was an organist who played a lot of French music, and I have played with modes for many years. Modes are not French, however. No one owns the modes. No one owns french fries, either, for those who are hungry.
If I play a C major triad and add the sixth degree, and move up a step and follow it with a D minor triad and an added sixth degree, am I French or jazz? Or both, or neither? Or worse: a C major 7th chord becomes THE tonic, and the first and final chord to my piece. Why might this potentially cause trouble?
Funny: it's not really right for either style. It's easy to hear why in jazz. It's impossible to say why in classical. It could be, or it couldn't be. Or one might be indifferent. One could write dissertations on the 7th degree's use and misuse and keynote packed lecture-halls, in music schools across the globe. The hunger of a theorist knows no satiety.
This leads easily into the angry area of clichés - and we might as well face this fact: if you can write it down, it has probably been done before and you are a possible victim of the dismissive "pastiche" review. These sentences make sense, and are therefore hackneyed: there must be a way to improve language - but at what expense (sense?).
Many classical musicians honor a few "great" jazz musicians who perhaps "crossed-over" (cross-dressed) successfully. Gershwin will get top bill for that honor. I'm not sure he was the best, but he still sells tickets to classical enthusiasts.
His career went alongside Ravel's, and Schoenberg's and Messiaen's, Victor Herbert's, and most interestingly, Duke Ellington's.
Music has no real fences: people create fences.
I have always wondered why someone had not very cleverly taken Beethoven's piano sonatas, reworked a few of them with "larger," lush and at one time Moderne harmonies and reaped the dollars, Pounds, Euros with the sensational results. And possibly, classical music might find a new direction in its scary future. A few steps back, a bit to the left, and forward again.
To think in tertiary dominants, the circle of fourths, and substitutions, alterations is much closer to what music really sounds like than the impossibly complex Schenker charts that turned me sour to theory at Queens College, many years ago. Learning 16th-century counterpoint is a worthy math assignment. I think it would be better than algebra, but not better than how to play songs by ear that people will know. Musicians used to be the smartest women and men in town: the encyclopedia of notes. When did classical musicians (keyboard artists/conductors) stop playing by ear, and stop improvising in public? When was the last time you heard a cadenza that was fresh and maybe a little thrilling, because it was obviously not rehearsed?
I'm perhaps too old, weatherbeaten to play the role of real renegade. Classical music so desperately needs an endlessly inquiring composer, somebody on the order of an after-Bernstein (at least in the USA) to pull listeners in by clever inventions, and forays into forbidden areas (Broadway) and pop-charts. This used to happen.
Classical music has pulled so far away from what people out there really listen to, or want to listen to that we are heading towards a concert hall of one. I live my invisible-composer life through that dream, but I know that it is false. I am not interested in money, and fame is for prettier people. I acknowledge that my many years studying theory in university and conservatory were crap - and that is not my fault.