in 1953, pianist George Russell published his Lydian Chromatic Concept of Tonal Organization, which offered an alternative to the practice of improvisation based on chords. Abandoning the traditional major and minor key relationships of Western music, Russell developed a new formulation using scales or a series of scales for improvisations. Russell's approach to improvisation came to be known as modal in jazz. Davis saw Russell's methods of composition as a means of getting away from the dense chord-laden compositions of his time, which Davis had labeled 'thick'. Modal composition, with its reliance on scales and modes, represented, as Davis put it, "a return to melody" (rovingeye2).
George Russell checked out last night.
The Concept lives on.