Twelve-bar blues

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The 12-bar blues (or blues changes) is one of the most popular chord progressions in popular music, including the blues. The blues progression has a distinctive form in lyrics and phrase and chord structure and duration. It is, at its most basic, based on the I-IV-V chords of a key.

The blues can be played in any key. Mastery of the blues and rhythm changes are "critical elements for building a jazz repertoire"(Thomas 2002, p. 85).

Contents

Structure

The blues progression, in C, is as follows[citation needed]:

C C C C   or   C7 C7 C7 C7
F F C C   or   F7 F7 C7 C7
G F C C   or   G7 F7 C7 C7 About this sound Play 
Different notations
Chord Function Numerical Roman
Numeral
Tonic T 1 I
Sub-dominant S 4 IV
Dominant D 5 V

Chords may be different with a few notation systems. 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. The tonic (in Roman numerals is also called the I, the sub-dominant the IV, and the dominant the V.

These three chords are the basis of thousands more pop songs which thus often have a blue sound even without using the classical 12-bar form. Using the above notations, the basic chord progression can be represented as follows.(Kernfeld 2007)

Function
T T T T
S S T T
D D T T
Roman numeral
I I I I
IV IV I I
V V I I

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.

[edit] Variations

Many variations are possible. The length of sections may be varied creating Eight-bar blues or Sixteen-bar blues.

Before the V-IV-I-I "shuffle blues" pattern became standard in the third set of four bars, the dominant chord continued through the tenth bar (Tanner and Gerow 1984, 37 cited in Baker 2004: "This alteration [V-IV-I rather than V-V-I] is now considered standard. (Tanner 37)."):

I I I I
IV IV I I
V IV I I

The common quick to four or quick-change (quick four(Alfred 2003, p.4)) variation uses the subdominant chord in the second bar:

I IV I I
IV IV I I
V IV I I


These variations are not mutually exclusive; the rules for generating them may be combined with one another (and/or with others not listed) to generate more complex variations.

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:

Using a seventh chord
I IV I I7
IV IV7 I I7
V IV I V7

When the last bar contains the dominant, that bar may be called a turnaround, otherwise the last four measures is the blues turnaround.

Basic jazz blues progression
I7 IV7 IVdim I7 Vm7 I7
IV7 IVdim I7 III7 VI7
IIm7 V7 III7 VI7 II7 V7

In jazz, 12 bar blues progressions are expanded with moving substitutions and chordal variations. The cadence (or last four measures) uniquely leads to the root by perfect intervals of fourths.

Bop V/ii cliche arpeggio, in second measure, upwards from third (C) to ninth (B): A79(Spitzer 2001, 62) the dominant of Dm (ii in C major) About this sound Play .

The Bebop blues(Spitzer 2001, 62):

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