Polymodal chromaticism is a musical term coined by composer, ethnomusicologist, and pianist Béla Bartók. The technique became a means in Bartók's composition to avoid tonality in the sense used between approximately 1600-1900 and yet a different approach than that used by Arnold Schoenberg and his followers in the Second Viennese School and later serialists.
Bartók had realised that both melodic minor-scales gave rise to four chromatic steps between the scales' 5th and the rising melodic minor-scale's 7th degrees when superimposed. Consequently, he started investigating if the same pattern could be established in some way in the beginning of any scales and came to realise that superimposing a Phrygian and a Lydian scale with the same tonic resulted in what looked like a chromatic scale. Bartók's twelve-tone Phrygian/Lydian polymode, however, differed from the chromatic scale as used by, for example, late-Romantic composers like Richard Strauss and Richard Wagner. During the late 1800s the chromatic altering of a chord or melody was a change in strict relation to its functional non-altered version. Alterations in the twelve-tone Phrygian/Lydian polymode, the other hand, were "diatonic ingrediences in a diatonic modal scale." (Béla Bartók Essays)
Phrygian mode (C): C - Db - Eb - F - G - Ab - Bb
Lydian mode (C):
C - D - E - F sharp - G - A - B
Twelve-tone Phrygian/Lydian polymode (C):
C - Db - D - Eb - E - F - F sharp - G - Ab - A - Bb - B
Melodies could be developed and transformed in novel ways through diatonic extention and chromatic compression, while still having coherent links to their original forms. Bartók described this as a new means to develop a melody.
Bartók started to superimpose all possible diatonic modes on each other in order to extend and compress melodies in ways that suited him, unrestricted by Baroque-Romantic tonality as well as strict serial methods such as the twelve-tone technique.
In 1941, Bartók's ethnomusicological studies brought him into contact with the music of Dalmatia and he realised that the Dalmatian folk-music used techniques that resembled polymodal chromaticism. Bartók had defined and used polymodal chromaticism in his own music before this. The discovery inspired him to continue to develop the technique.
