The rhythmic structure of the melody is interesting hypermetrically: in mm. 1–4, thehypermetric downbeat occurs in mm. 1 and 3 and emphasizes ^5 as the melodic anchor.The continuation of the phrase features a less regular hypermetric organization withmetrical downbeats occurring in mm. 5, 6, and 7. This hypermetric organization cor-roborates yet another characteristic of contrafacts, namely that they have a fairly irregularand purposefully unpredictable phrase structure. The irregular hypermetric organizationof the A section is balanced by a symmetrical unfolding of hypermetric two-bar phrasesin the bridge

With the exception of the blues, the rhythm changes progression is probably the mostimportant chord progression in jazz. The term “rhythm changes” refers to a 32-bar AABAform based on the harmonic structure of “I Got Rhythm” by George and Ira Gershwin.The song appeared in the Aarons and Freedley production Girl Crazy (1930) andoriginally featured a 34-bar AABA form with a two-bar extension in the last A section.The two-bar extension was eventually cut and the chord changes of the last A sectionreplicated those from the second A. A newly composed line based on the rhythm changesprogression is known as a contrafact. The enormous popularity of rhythm changes hasbeen well documented by an ever-increasing number of composed contrafacts andrecordings

Charlie Parker wrote a number of contrafacts on rhythm changes among which “Moosethe Mooche,” shown in Figure 19.1, is one of the most well known