Okay, first of all: what I’m talking about here is the “mainstream” jazz tradition, insofar as such a thing exists (you can make a good argument that it doesn’t, really). “Jazz” is a wide net to cast. To flip it around, if I were going to list things that aren’t “classical” music, I might say “use of the electric bass guitar” or even “microtonality.” Are those things really mutually exclusive with classical music? No. But they are not part of the tradition of the Viennese masters, not what your local community orchestra would play, not what most people think of when they think of classical music.
One misconception that many classical musicians seem to have about jazz is that since it has strong improvisatory elements, it must be very free and unstructured. I think the opposite is true: improvisation, at least in the mainstream-bebop/hard-bop-influenced style, requires fairly strict structural underpinnings. None of the following works well when someone is trying to improvise:
- Free forms. Form in jazz is much stricter than in classical music. Most common jazz tunes have one of two forms. The first is precisely 32 bars in 4/4 time, with four eight-bar sections: AABA. The second is precisely twelve 4/4 bars, a “blues” form. Anything that doesn’t fit exactly into one of these categories is most likely very closely related to one of them.
- Free harmony. Bebop and hard-bop jazz are extremely tonal. While improvisers may play pitches that fall “outside” the chords, it is almost always within a tonal framework: the notes function as upper extensions of the chords, or at least they are used in a sort of polychordal way that has reference to the underlying harmony and will ultimately resolve back to it. The idea that “there are no wrong notes” isn’t exactly true; notes can definitely sound very wrong if they aren’t properly contextualized with regard to the harmony.
- Free or changing meter. Jazz makes frequent use of polymeter and syncopation, which can give the impression of shifting meter, but most jazz doesn’t actually change meters, especially in improvisatory sections. The polyrhythms and syncopations work because they are overlaid on an unchanging metric pulse, and resolve to it.
- Rubato. Tempi also tend to quite strict in jazz playing. A musician might “lay back” in the beat or stretch a rhythm, but the underlying pulse doesn’t change. (In my experience, jazz players generally have much steadier internal metronomes than classical musicians.)
