Tonality is often described as a relationship between pitches and chords belonging to a single scale: in composing a melody to go with a (major) I-ii-V-I progression, the student of tonal music is taught to use pitches drawn from one diatonic collection. Minor-mode harmony, however, is invariably polyscalar. Both modal mixture and the use of secondary dominant chords increase the scalar density of tonal harmony. Impressionist composer and jazz musicians continued this process, regularly using all four of the locally diatonic scales (1), as well as (more sporadically) the other three scales derived in Section I-B (2). The result is a fascinating blend of middle ground diatonicism and local chromaticism, a music in which the qualities of "tension" and "release" are the products both of shifts between different scalar collections and of background movement among regions of a single, diatonic scale. Listening to Ravel's "Ondine" or to a sophisticated jazz musician improvise over standard tonal changes, one hears a curiously hybrid sound - a dense and difficult chromaticism that still seems rooted in elementary principles of tonal voice-leading.
One might conclude that the "common practice period" did not necessarily end with nineteenth century. The scales derived in Section I, coupled with the rules of "chord-scale compatibility" discussed in Section II, represent a substantial addition to the tonal system which is not the creation of any single musician. Though the expanded system is theoretically elegant, it evolved over a number of years, in the hands of a number of figures - Debussy, Ravel, Stravinsky, Bartók, Messiaen, Thelonious Monk, Charlie Parker, John Coltrane. All of these have explored various of the seven non-chromatic scales, like mountanieers climbing the same mountain from different sides, often unaware of the others' progress. In recent decades, their explorations have crystallized in the vocabulary of the working jazz musician. To this extent, at least, we do have a genuinely "common practice." And to this extent, tonality is not a relic of previous times, but rather something that continues to change and grow.
(1) Major, melodic minor, whole-tone and octatonic.
(2) Harmonic minor, harmonic major and symmetric augmented.
Los solos de músicos de jazz mencionados en el artículo están transcritos en la web del autor.