A way out of the complexities of
bebop, thanks, in great part, to
Miles Davis (and his friend
Gil Evans), with the "title track" ("Miles") of his
1958 Milestones LP, the entirety of
Kind of Blue (
1959), and the 1959/
1960 Miles/Evans
Sketches of Spain LP. By basing a
composition on a set of
modes, it gave the improvisor a chance to shape his/her melodies and phrases instead of wrestling with a complex set of chord changes (
John Coltrane was becoming the "Olympic wrestling champ" at the time, in his "Sheets of Sound" period) -- echoing Miles' previous use of
pedal point sections in tunes, in lieu of explicitly stated changes.
The idea slowly caught hold in the jazz world, and the 60's were, in part, about expanding on the ideas expressed in Kind of Blue, with generous helpings of 1) George Russell's textbook The Lydian Chromatic Concept of Tonal Organization (though it had roots -- and applications -- dating back to the 40's, it wasn't published, IIRC, until the early sixties), 1a) Nicolas Slonimsky's Thesaurus of Scales and Melodic Patterns, 2) Coltrane's 1959 Giant Steps, a combination of modal, modal-influenced blues, and a chord sequence later to be known as "Coltrane Changes", and 3) Ornette Coleman's new-at-the-time notions of a "free jazz", which became, for many young musicians, a continuous bazaar-in-progress vis-à-vis the cathedral, audience, and industry of bop.
The "problem" with Kind of Blue was that, for the most part, the chromaticism of bop was lost; the meal was still great, but it was missing a lot of the spicyness to which one had grown accustomed. At best, you could freely, and nicely, spin fairly-diatonic melodies from the sequence of modes; at worst, you treated it -- as many older bop musicians did over the years -- as a bop tune with a severely reduced chord progression, minus the familiar resolutions through a sequence of keys, mandated by the given chord progression.
Compare Wes Montgomery's mid-60's rendition of Coltrane's 1961-penned "Impressions" with Coltrane's own; Wes virtuosically (bop-wise) spins his wheels, lost with a tune that goes, harmonically, from Point A to Point B and back, over and over, while Coltrane (and his quartet/quintet) had incorporated the aforementioned new elements, defining the modern definition of modal jazz. The torch, both for "King of Jazz" and definer-of-modal-jazz passed from Miles to Trane in the year or two after Kind of Blue -- compare, again, two different recordings: Trane's solo on the studio version of "So What" hews, as did everyone else's, to the limits of the modes (the "A to B and back" that was, in fact, the basis for "Impressions"). The next year (1960), you can hear the difference, in a live version recorded in Stockholm, as he had found a way to incorporate both the emerging polytonality of his pre-modal "sheets of sound" approach and the real polytonality of superimposing extended "Giant Steps" sequences over the modal underpinning.
0) From Bill Evans' comping on parts of Kind of Blue: the use of quartal harmony in his piano voicings, providing a more harmonically-ambiguous backdrop for the soloists. This approach became a staple of Coltrane's group, and a signature sound associated with their pianist McCoy Tyner.
1) From Russell: polytonality -- in this context, the notion of superimposing other modes on top of the implied mode(s) of the tune. By the time his book was first published, 1953, he could only anticipate polytonal jazz; his own groups, later in the decade, featuring people like Evans and Eric Dolphy among its ranks, used a programmatic sort of polytonality in the compositional approach, with soloists asked to use certain modes in certain sections....
Rewrite in progress.