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My understanding is before 1970, few Jazz players thought about modes. For certain, Charlie Parker, Colman Hawkins, Bud Powell, Art Tatum, Monk, etc never thought in modes.

Barry Harris shows how they did think*, a simpler, deeper way: more true to the form before Kind of Blue. Russell's Modes, inspired by a fellow patient in a tuberculosis ward, and now taught as the foundation for improvisation, seem to me a projection of Western Academic ideas unto African American idioms, with little understanding or respect to the ideas behind those idioms. Basically a "takeover" of Jazz tradition by a counterculture generation of modern Jazz players, and explainers interested in creating course curriculum. The emphasis on "Modal Theory" and scales today appears way out of porportion to it's influence in the body of recordings we now classify as Jazz.

The modal approach was used to define and frame a new form with an extreme paucity of chords. Why is it relevant to the complex progressions which came before?

Please set me straight.

ref* Alternative to modal approach: http://bit.ly/2GsJpBm

My understanding is before 1970, no Jazz players thought about modes.

This is incorrect, see this question: How does modal jazz use chord progressions?

A: Modes became of interest over time as a way to organize what pitches to use over certain chords and sounds. This is a naturally arising phenomenon when there are many sounds to consider and memorize what notes work over each sound. Chord scales are a convenient way of organizing what notes to play over what chords, and chord scales are inherently modes. Naturally, musicians began to play around with these modes because they offered a different way of looking at the same notes they already knew. There was no "takeover", unless jazz musicians were trying to "take over" jazz itself and expand its lexicon with new ideas.

Modes seem to me a projection of Western Academic ideas unto african american idioms, with little understanding or respect to the ideas behind those idioms. Basically a "takeover" of Jazz.

This is a projection that jazz somehow existed before ... well, before it existed. The part I highlighted is also in my estimation an egregiously bad projection that ideas somehow aren't allowed to (or simply can't) meld into one another, borrow back and forth, and so on. This is bad because this is precisely how Jazz came about. Jazz arose out of the musical traditions centered around New Orleans at the turn of the 20th century, which was a hot pot of everything you could imagine - namely military march music, funeral march music, dance music of the time, and music played in brothels. Remember, also, that New Orleans was a very important port city in the 1800s, meaning that much influence also came from the Caribbean and various Hispanic nations to the south. Improvisation is also nothing new even to European music: Bach, Mozart, and Beethoven were well known in their day for being able to improvise - and in the Renaissance era, improvising over a cantus firmus was an important tool for teaching counterpoint (i.e., composition). However, improvisation in the way we think of it today tends to come out of the Jazz, Blues, and Rock idioms that developed in 20th century America.