The first movement of Béla Bartók’s 4th String Quartet seems to loosely emulate the classic Sonata form. While traditionally, the Sonatas composed in the classical era adhered to more regimented harmonic and thematic “rules”; Bartók’s piece seems to be more of a 20th century loose interpretation of the form which serves to offer some sort of structure to a dissonant and not traditionally tonal piece.
The first thirteen bars of the movement could be looked at as the first theme of the exposition. The first two bar phrase seems to be answered by another two bar phrase which is then followed by a longer phrase; this sentence also introduces the rhythmic motif in the first violin part which is repeated in the following two measures. The extremely chromatic melodic motion along with the intensely contrapuntal beginning, help introduce the dark and eerie mood of the piece. This is further emphasized by the canon-like entrances of the set (013) at measure 5 each transposed a minor second above the last which is followed by a sforzando on notes that are each a major second apart at measure 7. At measure 11 one of the most important rhythmic motive of the piece (three eighth notes followed by two sixteenth notes and another eighth) is introduced, which returns later at mm. 26, 55, and many other times throughout the piece. The set class for that melodic motive is (0123); a chromatic figure that also reappears many times. While it is hard to say that this principal theme is in any specific key due to this chromaticism and clustered texture, it does seem that C serves as a tonal focus around which the opening material revolves.
