In his introduction to "Béla Bartók Masterpieces for the Piano," Bartók explains that the Bagatelles represent a conscious departure from the Romantic piano style of the 19th century. The pieces mark a significant step in the development of his musical expression, with the integration of Hungarian and Slovak folk melodies, particularly in Bagatelles 5 and 6, revealing an innovative approach.
Right at the beginning of the collection, Bartók experiments with a radical approach to tonality, for example, by choosing different accidentals for each hand in the first Bagatelle—four sharps for the right hand, four flats for the left. This is among the earliest attempts at bitonality by a European composer, as Bartók later noted. The second Bagatelle is framed by a chromatic melody that extends over repeated major seconds and functions as an axis of symmetry. In the third bagatelle, the right hand creates a dense mist of sound with a continuous chromatic figure, while the left hand plays an expressive, sparse melody that particularly emphasizes the note F-sharp and is in tension with the key of C.
The fourth and fifth bagatelles draw on folk song melodies: number four is based on a Hungarian song that Bartók notated in 1907, which tells of a cowherd's sorrow. The fifth bagatelle is based on a Slovak song that Bartók heard in Grlica in 1908; it depicts the story of a boy who plants a white rose in front of a singer's house. Both melodies are pentatonic and significantly influence the compositional technique, with a rapid ostinato on the G minor seventh chord dominating the fifth bagatelle.[5]