Drawing upon analogies with pitch and dynamics, we hypothesize that there exists a durational alphabet in music out of which rhythmic and larger temporal events are built. The alphabet consists of the clustering of note durations into one of three elemental units: R(epetition), L(engthening), and S(hortening). Examples supporting this model are drawn from melodic lines by Bach, Mozart, Schubert, and Shostakovich. The study of the compositional use of R, S, and L, particularly in chains of two and three, is shown to be an effective tool for stylistic description and discrimination. Moreover, consistent and dramatic differences in the frequency of use of specific sequences of R, S, and L and chains of these symbols suggest normative, syntactical structures found in the standard Western repertoire.