Grouping is one of the two independent elements of rhythm in Western music. Grouping is defined as “the manner in which music is segmented at a whole variety of levels, from groups of a few notes up to the large-scale form of the work.” Grouping is more closely related to time spans than time points, the latter being more similar to meter. Specifically, groupoing deals with what takes place over specified durations, versus meter, which deals with moments in time. Moreover, grouping is associated with the wavelength aspect of pitch perception. (Clarke 478). One theory of grouping is explained in Lerdahl and Jackendoff’s Grouping Well-Formedness Rules.
Lerdahl and Jackendoff’s definition
Grouping is one of two ways to divide rhythm. According to Lerdahl and Jackendoff, groups exist in a hierarchy. There exist subordinate groups and dominate, or superordinate, groups. Thus, the grouping structure is recursive. Lerdahl and Jackendoff define a number of rules classifying and defining groups. An important rule is that non-adjacent units cannot group together.
Grouping is distinct from meter. As Lerdahl and Jackendoff point out, groups do not have an inherent metrical accent. Groups may start on metrical downbeats or on weaker beats. The phase relationship between groups and the meter create rhythmic dynamism. Additionally, beats do not have inherent grouping. In a metrical structure, a beat is merely part of a pattern that can start and stop anywhere.
Lerdahl and Jackendoff also do not like Cooper and Meyer’s rhythmic notation, which puts accents on groups. For Lerdahl and Jackendoff, this accent should arise out of the metrical nature of the piece.
(Lerdahl and Jackendoff, 1983)