form

The basic plan or temporal structure of a piece of music. The simplest forms are binary form, which consists of two sections often separated by a double bar (marking off a section), and simple ternary form, which consists of three sections - the first section, followed by a contrasting section, returning to the first section as in song form: ABA. Most larger-scale forms are an expanded and developed version of these two basic types. Examples include sonata form and rondo form. During the 19th century, Romantic composers such as Richard Wagner broke away from classical forms, using returning motifs (called leitmotifs) to unify the work. These composers tended to take more interest in literature.

In the 20th century form changed in order to accommodate new parameters in harmonic development and rhythm. Béla Bartók's string quartets use alternating sections of different length, and later the composer Witold Lutosławski invented ‘chain form’, where contrasting sections link over each other to provide large-scale development in the piece. Chance-based operations such as those of John Cage in Music of Changes (1951) often, paradoxically, produced clear and differentiated structures, although different each time.