This dissertation posits that an essential aspect of temporal experience in Bach's keyboard fugues resides in the interaction of their inherent repetition with a general, unsystematic trend toward longer phrases as the pieces unfold, and it inquires into how this interaction takes place. This inquiry necessitates a subsidiary inquiry into the segmentation schemes operative in these fugues and into how these schemes promote phrase-rhythmic continuity. Analytical methodologies draw mainly from Schenkerian theories of phrase rhythm, as exemplified by the work of William Rothstein and Channan Willner, while interpretation refers to recent scholarship on musical meaning, as represented by the work of Robert Hatten and Steve Larson, and to the observations of Johann Mattheson, who wrote sensitively about the experience of repetition in fugues, and Ernst Kurth, who described qualities of fluidity that pervade the fugues of Bach, among others.

After Chapter 1 introduces the scope of the dissertation's investigations, Chapter 2 surveys the literature on fugue that impinges on phrase rhythm. The survey is arranged in four categories: literature on how thematic repetition interacts with segmentation, literature on the rhythm of repetition, literature on motion and fluidity, and literature on durational spans. Methodological foundations in Chapter 3 include Rothstein's "imaginary continuo," grouping, meter, tonal rhythm, sequences, and the Fortspinnungstypus; this chapter introduces my distinction between "literal" and "figurative" grouping, which addresses problems of grouping in polyphonic textures, and my notion of "thematic rhythm," whereby impressions of rhythmic equivalence among thematic repetitions color our experience of repetition. Chapter 4 then focuses on segmentation at the levels of the phrase and the period, and it proposes certain types of "compound" phrases in which thematic repetition associates with segments longer than the original subject. It also identifies some vehicles of continuity among segments, including "deep thematic overlap," in which a subject crosses the boundary of two segments and may inspire gestural interpretation; and "counterphrasing," in which rhetorical and tonal goals of phrases are separated, engendering fluidly ambiguous impressions of phrase or period articulations. Finally, Chapter 5 investigates the generation of longer phrases through the enlargement of a fugue's subject.