William Caplin

The theory is grounded in eighteenth-century compositional pedagogy[6] and in work by Arnold Schoenberg and his pupil Erwin Ratz.

"[8] Schoenberg’s concept of the "basic idea" (here understood as a two-measure unit)[12] and his distinction between period and sentence—two models for themes—are the foundation for a theory based on a dichotomy between "tight-knit" and "loose" designs and on "beginning," "middle," and "end" functions.

The core figure is the theme (understood paradigmatically as eight bars in length), but formal functions can be extended outward to form sections and entire movements.

The theory has, nevertheless, been criticized for a "zeal for exhaustive theoretical and terminological rigor" that can interfere with that flexibility in analysis, and specifically for its "dogged adherence to a rigidly quadratic conception of grouping structures" [source needed, linked source does not contain any of these quotes]; that is, to ideas defined as two bars and themes defined as eight bars.

[17] A related criticism is Caplin's "tendency to substitute [a formal/functional] archetype for the music in question as the point of reference for analytical discussion.

"[18] Although intended for, and derived specifically from, the music of Haydn, Mozart, and Beethoven, the theory of formal functions has been extended by various authors, mostly to later repertoires and largely in connection with the sentence paradigm (notably, Schubert, Schumann, Wagner, Schoenberg, and music in film) but occasionally earlier as well (especially J.S.