The twelve-bar blues (or blues changes) is one of the most prominent chord progressions in popular music. The blues progression has a distinctive form in lyrics, phrase, chord structure, and duration. In its basic form, it is predominantly based on the I, IV, and V chords of a key. Mastery of the blues and rhythm changes are "critical elements for building a jazz repertoire".
Chords may be also represented by a few different notation systems such as sheet music and electronic music. A basic example of the progression would look like this, using T to indicate the tonic, S for the subdominant, and D for the dominant, and representing one chord. In Roman numeral analysis the tonic is called the I, the sub-dominant the IV, and the dominant the V. (These three chords are the basis of thousands of pop songs, which thus often have a blues sound even without using the classical twelve-bar form.)
The first line takes four bars, as do the remaining two lines, for a total of twelve bars. However, the vocal or lead phrases, though they often come in threes, do not coincide with the above three lines or sections. This overlap between the grouping of the accompaniment and the vocal is part of what creates interest in the twelve bar blues.
"W.C. Handy, 'the Father of the Blues', codified this blues form to help musicians communicate chord changes." Many variations are possible. The length of sections may be varied to create eight-bar blues or sixteen-bar blues.
Quick to four
Seventh chords are often used just before a change, and more changes can be added. A more complicated example might look like this, where "7" indicates a seventh chord:
|ii7||V7||I7 V/ii♭9||ii7 V7|
This progression is similar to Charlie Parker's "Now's the Time", "Billie's Bounce", Sonny Rollins's "Tenor Madness", and many other bop tunes. "It is a bop soloist's cliche to arpeggiate this chord [A7♭9 (V/ii = VI7♭9)] from the 3 up to the ♭9."
There are also minor twelve-bar blues, such as John Coltrane's "Equinox" and "Mr. P.C.". The chord on the fifth scale degree may be major (V7) or minor (v7). Major and minor can also be mixed together, a signature characteristic of the music of Charles Brown.
While the blues is most often considered to be in sectional strophic form with a verse-chorus pattern, it may also be considered as an extension of the variational chaconne procedure. Van der Merwe (1989) considers it developed in part specifically from the American Gregory Walker, though the conventional account would consider hymns to have provided the repeating chord progression or harmonic formulae of the blues.
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- Kernfeld 2007
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