The blues has evolved and changed over the course of the 20th Century.
Earliest style of blues, rulral blues, relied on basic I – V – V chord progressions in 3 phrases, typically in this format:
1. statement
2. reiteration of statement
3. response
Although the blues form later became standardized to consist of 3 phrase of 4 bars each (for a total of 12 bars), rural blues songs were often not so symmetrical, with extra bars or beats often added to the phrases.
Basic Blues Progression:
I I I I
IV IV I I
V7 IV I I
This progression could also occur in a minior key but it typically featured major triads to which the flatted 3rd was often added, creating a blue note.
A common variation employed the IV or V chord in the second bar, omitted the IV chord from teh 10th bar and added a V7 chord in the last bar (referred to as the turnaround)
Eb (I) Bb7 (V7) Eb (I) Eb (I)
Ab(IV) Ab (IV) Eb (I) Eb (I)
Bb7 (V7) Bb7 (V7) Eb(I) Bb7+5 (V7)
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Early jazz composers i New Orleans and Chicago began adding some passing chords and chord substitutions to the basic blues progresssion.
Although diatonic chords comprised the majority of the chords,
- secondary dominant chors began to be employed such as V/IV in the 4th bar (a dominant chord built on the tonic) ,
- a V/ii in the 8th bar (a dominant chord built on the 6th scale degree)
- and a V/V in the 9th bar ( a dominant chord built on the 2nd scale degree)
Passing diminished chords and chord inversions also were used, particularly in the second or 6th bar to create smooth bass lines.
C(I) F (IV) C(I) C7 )V7/IV)
F (IV) F#dim7 (viidim7/V) C/G bass (I6/4) — only 3 bars on this line
A7 (V7/ii) D7 (V7/V) G7 (V7) C (I) C (I)
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The swing era did not add an abundance of new chord sub to the blues form, however the 6th, 7ths and 9ths were frequently added to the chords.
The tonic chord was typically a major 6th chord, a minor 6th chord or a dominant 7th chord.
The latter creates a dominant tonality which is not commonly found in Western harmony.
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The bepob ear brought a significant amt of h armonic variation and chord sub to the blues form.
The IV chord in the 2nd bar and the V/ii chord in the 8th bar b oth became common place.
Bars 9 and 10 as well as the final bar (the turnaround) were typically ased on ii-V progressions.
F7 (I7) Bb7 (IV7) F7 (I7) F7 (I7)
Bb7 (IV7) Bdim (vii dim7/V) F7/C D7 (V7/ii7)
Gm7 (ii7) C7 (V7) F7 (I7) Gm7 (ii7) C7 (V7)
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Blues scale:
— a 6-note scale consisting of the ascending pattern:
–minor 3rd, whole step, half step, half step,. minor 3rd, whole step
C Eb F F# G Bb C
C blues scale:
the pitches that are a minor 3rd and an aug 4th or dim 5th above the tonic are often referred to as ‘blue notes’. These are actually an approximation of true ‘blue notes’ which are bent pitches that lie in between the minor and major 3rd and the dim and perfect 5th.
The blues scale maybe used in any type of composition to color the minor 7th or dom 7th chords. In rare instances, it has even been used over major 7th chords.
When it is used over a dom 7th chord, the minor 3rd of the scale adds an aug 9th (usually written as a minior 10th) to the chord.
The blues scale built on the root of the I chord can be used to color all of the chords in the basic blues progression. This great simplifies improvising on the blues because the player needs to be concerned with only one scale. Because of its lack of flexibility to imply chord sub, the blues sclae is best used in combination with other scale choices.