thumb|upright=1.4|32-bar rhythm changes in B, as commonly used for improvisation (slashes indicate [[rhythm section|rhythm chordal instrument improvised comping)]]
The Rhythm changes is a common 32-bar jazz chord progression derived from George Gershwin's "I Got Rhythm". The progression is in AABA form, with each A section based on repetitions of the ubiquitous I–vi–ii–V sequence (or variants such as iii–vi–ii–V), and the B section using a circle of fifths sequence based on III<sup>7</sup>–VI<sup>7</sup>–II<sup>7</sup>–V<sup>7</sup>, a progression which is sometimes given passing chords.
This pattern, "one of the most common vehicles for improvisation," 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" as well as Charlie Christian's "Seven Come Eleven," Dizzy Gillespie's "Salt Peanuts," recording of "Shag" (two years after the first performance of "I Got Rhythm" on Broadway) with his "New Orleans Feetwarmers" group.
In pop culture, "Meet the Flintstones", (c. 1960, Curtin/Hanna/Barbera) is based on the rhythm changes, thereby being a contrafact of "I Got Rhythm".
History
This progression's endurance in popularity is largely due to its extensive use by early bebop musicians. The chord changes began to be used in the 1930s, became common in the '40s and '50s, and are now ubiquitous. First, "I Got Rhythm" was by then already a popular jazz standard. 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. Third, using a stock, well-known progression for new melodies made it easier to perform a song at jam sessions, shows, and recordings because the bandleader could tell new musicians that the song uses rhythm changes and note any modifications and chord substitutions.
For contemporary musicians, mastery of the 12-bar blues and rhythm changes chord progressions are "critical elements for building a jazz repertoire".
Chords
<!--this article uses Roman numeral analysis and Chord names and symbols (popular music)-->The rhythm changes is a 32-bar AABA form with each section consisting of eight bars, and four 8-bar sections. In roman numeral shorthand, the original chords used in the A section are:
:{| class="wikitable" style="text-align:left; width:300px;"
|-
| width="25%" | I vi
| width="25%" | ii V
| width="25%" | I vi
| width="25%" | ii V
|-
|}
a 2-bar phrase, I−vi−ii−V (often modified to I–VI–ii–V), played twice,
:<score sound="1">
{
\new ChordNames \with {
\override BarLine #'bar-extent = #'(-2 . 2)
\consists "Bar_engraver"
}
\chordmode {
\override Score.BarNumber.font-size = #0
\override Score.BarNumber.stencil= #(make-stencil-boxer 0.1 0.25 ly:text-interface::print)
\set Score.barNumberVisibility = #all-bar-numbers-visible
\set Score.currentBarNumber = #17
\bar ""
d1:7 | d:7 | g:7 | g:7 |
\break
c:7 | c:7 | f:7 | f:7 \bar "||"
} }
</score>
The B section is followed by a final A section
:<score sound="1">
{
\new ChordNames \with {
\override BarLine #'bar-extent = #'(-2 . 2)
\consists "Bar_engraver"
}
\chordmode {
\override Score.BarNumber.font-size = #0
\override Score.BarNumber.stencil= #(make-stencil-boxer 0.1 0.25 ly:text-interface::print)
\set Score.barNumberVisibility = #all-bar-numbers-visible
\set Score.currentBarNumber = #25
\bar ""
bes2:maj7 g:7 | c:m7 f:7 | bes:maj7 g:7 | c:m7 f:7 |
\break
f:m7 bes:7 | es:maj7 aes:7 | c:m7 f:7 | bes1:maj7 \bar "|."
} }
</score>
Variant versions of changes are common due to the popularity of adding interest with chord substitutions, passing chords, and changes of chord quality. Bebop players, for instance, would often superimpose series of ii–V progressions (passing sequences of minor seventh and dominant seventh chords) or other substitutions for interesting or in order to discourage less experienced musicians from "sitting in" on the bandstand. The opening I chord was B<sup>6</sup> in Gershwin's original, but beboppers changed it to B<sup>M7</sup> or B<sup>7</sup>. For instance, the B section may appear as follows:
:<score sound="1">
{
\new ChordNames \with {
\override BarLine #'bar-extent = #'(-2 . 2)
\consists "Bar_engraver"
}
\chordmode {
\override Score.BarNumber.font-size = #0
\override Score.BarNumber.stencil= #(make-stencil-boxer 0.1 0.25 ly:text-interface::print)
\set Score.barNumberVisibility = #all-bar-numbers-visible
\set Score.currentBarNumber = #17
\bar ""
a1:m7 | d:7 | d:m7 | g:7 |
\break
g:m7 | c:7 | c:m7 | f:7 \bar "||"
} }
</score>
An even more adventurous bebop-style substitution is to convert C<sup>7</sup> | C<sup>7</sup> | F<sup>7</sup> | F<sup>7</sup> to Gm<sup>7</sup> | C<sup>7</sup> | Cm<sup>7</sup> | F<sup>7</sup>, and then further develop this substitution by changing this to Am<sup>7</sup> D<sup>7</sup> | Gm<sup>7</sup> C<sup>7</sup> | Dm<sup>7</sup> G<sup>7</sup> | Cm<sup>7</sup> F<sup>7</sup>.
Examples
thumb|upright=1.4|32-bar rhythm changes in B[[File:Rhythm changes complete in B-flat Ellis.mid]]
The following is a partial list of songs based on the rhythm changes:
{| class="wikitable sortable"
|+ "Rhythm Changes" contrafacts
|-
! Song !! Composer !! Year !! Source
|-
| "Anthropology" || Charlie Parker/Dizzy Gillespie || 1946 ||
|-
|"Dexterity"||Charlie Parker||||
|-
|"Lester Leaps In"||Lester Young||1939||