Wolfgang Amadeus Mozart‘s String Quartet No. 15 in D minor K. 421/417b, the second of the Quartets dedicated to Haydn and the only one of the set in a minor key, is believed to have been completed in 1783. The quartet is, however, undated in the autograph. It is in four movements:
1. Allegro moderato
2. Andante (F major)
3. Menuetto and Trio (the latter in D major). Allegretto
4. Allegretto ma non troppo
The first movement is characterized by a sharp contrast between the aperiodicity of the first subject group, characterized by Arnold Schoenberg as “prose-like,” and the “wholly periodic” second subject group. In the Andante and the Minuet, “normal expectations of phraseology are confounded.” The main part of the Minuet is in minuet sonata form, while “the contrasting major-mode Trio … is … almost embarrassingly lightweight on its own … [but] makes a wonderful foil to the darker character of the Minuet.” The last movement is a set of variations.