Twelve bar blues is a chord progression, typical of blues and later influenced musics. In addition to the harmonic formulae the twelve bar blues uses a rhythmic scheme of twelve 4/4 bars to the verse.

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 per measure:

T T T T
S S T T
D S T T

The first line takes 16 quarter note beats (4 measures X 4 beats), as do the remaining two lines (for a total of 48 beats and 12 measures). 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.

Many variations are possible. For instance, 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:

T  S  T  T7
S  S7 T  T7
D  S  T  D7

When the last bar contains the dominant, that bar can be called a turnaround .

Finally, here is an example showing the pattern in the key of D, and how it fits with the lyrics of a given verse. One chord symbol is used per beat, with "-" representing the continuation of the previous chord:

D        -     -      -        
Woke up this morning with the 

G     -   -    -   D - - - D7 - - - 
blues down in my soul 

G        -     -      -        
Woke up this morning with the 

G7    -   -    -   D - - - D7 - - -
blues down in my soul            Saying "My

A     -        -     A7
baby gone and left me, got a 

G    -    -     G7 D - - - D - A A7
heart as black as coal"

While the blues is most often considered to be in sectional strophic form with a verse-refrain 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 as the provider of the blues repeating chord progression or harmonic formulae (Middleton 1990, p.117-8).

Examples include Muddy Water 's "Train Fare Blues" (1948), Howlin' Wolf's "Evil" (1954), and Big Joe Turner's "Shake, Rattle, and Roll" (1954). (Covach 2005, p.67)

See also: eight bar blues, thirty-two-bar form.

Source

• Covach, John. "Form in Rock Music: A Primer", in Stein, Deborah (2005). Engaging Music: Essays in Music Analysis. New York: Oxford University Press. ISBN 0195170105.
• Middleton, Richard (1990/2002). Studying Popular Music. Philadelphia: Open University Press. ISBN 0335152759.
• Van der Merwe, P. (1989). Origins of the Popular Style. Oxford.