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

Chapter 19 provides an analysis of Charlie Parker’s “Moose the Mooche” and Hank Jones’simprovised solo on the tune. This chapter also proposes a pedagogy of rhythm changesimprovisation.