Rhythm changes

This pattern, "one of the most common vehicles for improvisation,"[2] forms the basis of countless (usually uptempo) jazz compositions and was popular with swing-era and bebop musicians.

For example, it is the basis of Duke Ellington's "Cotton Tail"[3] as well as Charlie Christian's "Seven Come Eleven,"[4] Dizzy Gillespie's "Salt Peanuts,"[4] and Thelonious Monk's "Rhythm-a-Ning".

Second, by listening to the song and writing a new melody over its chord changes, thereby creating a composition of a type now known as a contrafact, a jazz musician could claim copyright to the new melody rather than acknowledge Gershwin's inspiration and pay royalties to Gershwin's estate.

For contemporary musicians, mastery of the 12-bar blues and rhythm changes chord progressions are "critical elements for building a jazz repertoire".

For instance, Charlie Parker's "Scrapple from the Apple" and Juan Tizol's "Perdido" both use a different progression for the A section while using the rhythm changes bridge.