If there is a single term that describes a dominate feature for all types of jazz, I think that single term is improvisation (no doubt others might not think this way, but this focus works for me). Furthermore, I believe that a proper definition of Jazz should discuss both the process used to create the music and discuss the finished product with the emphasis on the process of creating the music over the sound, texture, and architecture of the finished product.
The creative process for Jazz addresses the approach used to assemble ideas and chord structures into a platform that supports improvisation. The structure or song architecture is built with space to created new solos to enable the musician to create material on the fly. The scale, tempo, and rhythm pattern are part of the decision process when forming the song architecture. Then, when creating the finished product, the soloist applies the scale to the chord platform in a way that is interesting to hear but does not obscure the rhythm of the song.
When defining a type of Jazz music that is focused on the application of unusual scales to modest chord arrangements (platforms), we are generally talking about Modal Jazz (this is not always the case, but is generally the norm). In really thinking about what style of Jazz I create, I have concluded that I partially fit into the circle of Modal Jazz. A musical “mode” is defined by Webster’s dictionary as “an arrangement of the eight diatonic notes or tones of an octave according to one of several fixed schemes of their intervals.” From a musicologist viewpoint, the term Mode is a synonym used to encapsulate the various Greek music scales that can be used to create a solo or a melody (or both).
I recall from my Jazz classes in College, there were theoretical attempts to describe the modes that reach back to the Greeks and Aristoxenus (c. 350 B.C.). There were other attempts at modal analysis from medieval musicology scholars such as Guido of Arezzo, Boethius, or Saint Ambrose. In the Renaissance period, the use of modes was discussed by musicians such as Tinctoris in the late 1400’s. Then the musicologist interest with modes fades, with the exception of strong use of modes by 18th and 19th century Irish folk music song writers. In the 20th century, a reemergence occurs, we have Jazz musicians using modes to enhance improvisation. The iconic album, a Touch of Blue (by Miles Davis), is often considered to be a hallmark for Modal Jazz. Many musicians (including Miles) were exploring this approach in the late 50’s through the mid 60’s. This exploration continued as Modal Jazz morphed into Fusion Jazz.
Before Modal Jazz emerged in the early 60’s, the usual approach for Jazz soloists was to start with a melody that was driven by the chord structure; then create adjustments to the melody that stayed within the boundaries set by the chord arrangement. My friends who made music during this period (early 50’s); tell me the focus for improvisation was to interpret the melodies. In almost all jazz prior to 1960, the notion of improvisation involved the selection of harmonies (replacing each note in the melody with an alternate note). Gifted improvisers like Louis Armstrong, created beautiful alternate counter melodies; the result was amazing jazz.
Clearly, before the Modal approach became part of the American Jazz scene, melodic improvisation and chord changes were accomplished within the regional use of Jazz standards. The chord structure and the initial melody of the Jazz standards placed firm boundaries on the selection of alternate melodies. Jazz musicians, I have visited with over the years, tell me that many players in the 40’and 50’s had become weary of the same well-trodden improvisatory approach for playing Jazz standards. When Modal Jazz came along, musicians jumped into the new concepts looking for fresh ideas and freedom from melodies and the chord changes in the arrangement. These ideas filtered into the solo approach used by early rock soloists on the west coast as the focus shifted from releasing singles (45 RPM records) to releasing LP (Long Play) albums (33 RPM records).
“You don’t have to worry about [chord] changes and you can do more with the [solo] line. It becomes a challenge to see how … inventive you can be. When you’re [solo is] based on chords, you know at the end of 32 bars that the chords have run out and there’s nothing to do but repeat what you’ve just done—with variations. When you go this [new] way [with modes]; you can go on forever.” “There will be fewer chords [in the song] but infinite possibilities as to what to do with them. “ — Miles Davis