The title, borrowed from Paul Henry Lang's description of Haydn's op. 20 string quartets in Music in Western Civilization, characterizes Haydn's endeavor to create more independent partwriting in the string quartet. First, Haydn's fugal practice is noteworthy particularly for the construction of the fugal exposition and his treatment of multiple subjects, the question of what constitutes a regular countersubject, and the treatment of redundant entries. Second, the chief strategy in these movements is the invention of invertible counterpoint in three voices. Haydn writes a double fugue (with a regular countersubject), as well as a triple and quadruple fugue, in which the principal issue is the ability of each subject (including the double fugue's countersubject) to serve as any voice——top, middle or bottom——in a texture of invertible counterpoint.
The expertise he attained with these works then allows him to exploit the technique in later quartets, principally in the development sections of sonata-form movements. There, he uses invertible counterpoint to establish the independence of each voice, and to create longer passages unarticulated by cadences, sections distinct from the more clearly articulated periodic expositions and recapitulations. The three fugal finales of op. 20, therefore, constitute Haydn's advanced study not so much in fugal procedure as in the practice of invertible counterpoint.
Learning Sonata Form Structure on Mozart’s String Quartets
