Paul Wilson lists as the most prominent characteristics of Bartók's music from late 1920s onwards the influence of the folk music of rural Hungary and eastern Europe and the art music of central and western Europe, and his changing attitude toward (and use of) tonality, but without the use of the traditional
harmonic functions associated with major and minor scales (Wilson 1992, 2-4).
Bartók is an influential
modernist and his music used or may be analysed as containing various modernist techniques such as
atonality, bitonality, attenuated harmonic function,
polymodal chromaticism, projected sets, privileged patterns, and large set types used as source sets such as the equal tempered twelve tone aggregate,
octatonic scale (and
alpha chord), the diatonic and heptatonia seconda seven-note scales, and less often the whole tone scale and the primary pentatonic collection (Wilson 1992, 24-29).
He rarely used the simple aggregate actively to shape musical structure, though there are notable examples such as the second theme from the first movement of his
Second Violin Concerto, commenting that he "wanted to show Schoenberg that one can use all twelve tones and still remain tonal". More thoroughly, in the first eight measures of the last movement of his
Second Quartet, all notes gradually gather with the twelfth (G♭) sounding for the first time on the last beat of measure 8, marking the end of the first section. The aggregate is partitioned in the opening of the
Third String Quartet with C♯-D-D♯-E in the accompaniment (strings) while the remaining pitch classes are used in the melody (violin 1) and more often as 7-35 (diatonic or "white-key" collection) and 5-35 (pentatonic or "black-key" collection) such as in no. 6 of the
Eight Improvisations. There, the primary theme is on the black keys in the left hand, while the right accompanies with triads from the white keys. In measures 50-51 in the third movement of the
Fourth Quartet, the first violin and 'cello play black-key chords, while the second violin and viola play stepwise diatonic lines (Wilson 1992, 25). On the other hand, from as early as the Suite for piano, op. 14 (1914), he employed maximally distributed, multi-aggregate, compound interval cycles in a
serial technique (Gollin 2007).
Ernő Lendvai (1971) analyses Bartók's works as being based on two opposing systems, that of the
golden section and the
acoustic scale, and tonally on the
axis system (Wilson 1992, 7).
Milton Babbitt, in his 1949 critique of Bartók's string quartets, criticized Bartók for using tonality and non tonal methods unique to each piece. Babbitt noted that "Bartók's solution was a specific one, it cannot be duplicated." Bartók's use of "two organizational principles"—tonality for large scale relationships and the piece-specific method for moment to moment thematic elements—was a problem for Babbitt, who worried that the "highly attenuated tonality" requires extreme non-harmonic methods to create a feeling of closure.
The cataloguing of Bartók's works is somewhat complex. Bartók assigned opus numbers to his works three times, the last of these series ending with the Improvisations Op. 20 in 1920. He ended this practice because of the difficulty of distinguising between original works and ethnographic arrangements, and between major and minor works. Since his death, two full and one partial attempts at cataloguing have been made. The first, and still most widely used, is
András Szöllősy's chronological Sz. numbers, from 1 to 121.
Denijs Dille subsequently reorganised the juvenilia (Sz. 1-25) thematically, as DD numbers 1 to 77. The most recent catalogue is that of
László Somfai; this is a chronological index with works identified by BB numbers 1 to 129, incorporating corrections based on the
Béla Bartók Thematic Catalogue.