12 Bar Blues Chords

Chords in the 12 bar blues sequence

Blues breaks the rules of conventional jazz harmony and improvisation.

The distinctive sound of blues chords is often created by the flattening of various notes (mainly the 3rd, 5th and 7th). The harmony often becomes ambiguous as the flattened 3rd will often be used in a melody at the same time as the major 3rd in the accompanying harmony. (Not the other way round: in a minor blues all 3rds are flattened).

There is a blues scale which contains these notes, however in a major key most players combine the flattened notes with the natural notes.

Do I play a different scale for each chord?

No – that’s the good news: one scale fits all. When you play the blues the same scale (based on the key you are in) is used over all three areas, i.e. in the key of C you use a C blues scale and do not usually change to an F blues scale for the F7 chord at bar 5. The resulting dissonances are effective depending on the players taste and feel for the blues.

You said “that’s the good news” what’s the bad news?

The bad news is that although the blues scale fits OK, so it is easy to start off playing a reasonable blues solo, it can become boring quite quickly to just  use this one scale.

When looking at the more basic 12 bar blues chord sequences (i.e. those in blues music rather than some of the more sophisticated jazz/blues) it does not usually make sense to use the RN analysis in the same way that we have been used to where key centres are defined by dominant chords. The flattened 7th is often used on tonic and subdominant chords purely as colour and need not imply a V7-I cadence or a secondary dominant.

If this makes no sense, then now would be a good time to read (or re-read) the Jazz Beginnersand/or Rock & Blues Beginners pages

Example:In the key of C the C7 chord in bar 4 of a typical 12 bar blues (see below Ex: 12a) appears to be a secondary dominant chord (V7 of IV), but it is more in keeping with the genre to think of the 5th and 6th bars as the subdominant rather than a new key centre. The IV chord is very often a IV7, but the F7 at bar 6 is chord IV7 of C, not chord V7 of Bb. Although theoretically you could think in terms of the RN analysis we have been using, and play a scale of F Mixolydian (mode starting on F using notes of the Bb major scale) this is unlikely to sound good.

I IV7 I I7 IV7 IV7 I I V7 (IV7) I V7

ex 12a: A very basic 12 bar sequence
This sequence was often slightly modified in swing, R & B and boogie-woogie of the thirties:

I IV7 I I7 IV7 IV7 I I IIm7 V7 I IIm7 V7

ex 12b
Often the secondary dominant is used in bar 8:

I IV7 I I7 IV7 IV7 I VI 7 IIm7 V7 I IIm7 V7

Ex 12c
There are also 12 bar sequences in a minor key:

Im IVm7 Im7 I7 IVm7 IVm7 Im7 Im7 bVI 7 V7 I IIm7-V7

ex 12d: A typical minor blues
N.B. In all of these sequences chord I is a triad (except on bar 4). In jazz blues sequences the tonic chord can be a major 7, however this is rare in real blues where chord I is either a triad, a dominant 7th chord or a 6th chord (the added note is used for colour rather than harmonic function as mentioned above), except on bar 4 where it is nearly always a dominant 7th leading to the IV chord on bar 5.

Practical Example of 12 Bar Sequences:


C C C C7
F7 F7 C C
G7 G7 or F7 C C-G7

Although some or all of the tonic and subdominant chords may have a minor 7 added, this is a blue  note and does not have its usual harmonic function as a dominant chord (except in bar 4 where it acts a secondary dominant leading to the IV7 chord). The above example only introduces the 7th to the tonic at bar 4 to emphasise this chord change. It is not a modulation to IV as it would be in classical harmony.
Blues musicians tend to use phrases and patterns rather than scale runs, though jazz variations of blues can be based on a 12 bar blues structure and can include jazz and blues style patterns alongside each other.

Jazz Blues

A simple jazz blues sequence usually changes to chord IV at bar 2 and back to chord I at bar 3 and uses a IIm7 V7 at bar 9 (often preceded by a secondary dominant).
Early 12 bar jazz  sequence (Typical of swing or jump)

C F7 C C7
F7 F7 C C or A7
Dm7 G7 C Dm7-G7

This type of sequence is typical of 1930s-1950s swing, jump and R&B styles. More complex sequences were used in bebop
Typical bebop blues changes

C F7-F#o7 C Gm7-C7
F7 F#o7 C-Dm7 Em7-Eb7
Dm7 G7 C-Am7 Dm7-G7

Form of the 12 bar

There are always three 4 bar phrases (ex 9e):

  1. Tonic (sometimes with a subdominant on bar two)
  2. Subdominant and back to tonic (often with repeat of first melody and lyric)
  3. Dominant (sometimes via subdominant) back to tonic (often with different melody and lyric)

jazz and blues theory

ex 12e: phrases in 12 bar blues.

As you can see, the second phrase is altered slightly to fit the different chords. This is extremely typical.

A very useful rule to remember:

This alteration of the 3rd note of the tonic scale from major on the I chord to minor as it becomes the 7th of the IV chord is extremely useful when composing or improvising any type of blues.

In jazz, blues sequences can become quite complex but still retain these 3 areas

There are other blues sequences, usually adaptations or extensions of the typical 12 bar. When a jazz musician says: “let’s play a blues,” they often mean a 12 bar with a II-V in bar 9, usually with the secondary dominant or more sophisticated changes (ex 12c). Blues players usually indicate to the band whether they want a V-IV or II-V type sequence.

Blues scales

We use more than one blues scale, (and rarely use the blues scale in its entirety) however the scale that has come to be called the blues scale is similar to a minor pentatonic scale but with a #4th (or b5th) added. (ex 12g). I shall refer to this as the minor blues scale but bear in mind it can be used in major and minor blues sequences.

jazz theory

ex 12g: Minor blues scale

This scale can be used over all the chords of a basic 12 bar sequence, so in the key of C a C blues scale can be used over the F7 and G7 as well as the tonic chord. (Apparent wrong notes are acceptable in the context of blues, but the best place for them is usually dictated by experience and a feel for the style rather than academic rules).

The secret of convincing use of the blues scale is to add a major 3rd (ex 12h) or combine it with a scale which is commonly used in rhythm and blues, swing or jump music. We call this the major blues scale (ex 12i).

jazz theory

ex 12h: Juxtaposition of minor and major

jazz theory

ex 12i: Major blues scale

jazz theory

ex 12j: Major blues scale combined with minor blues scale

These scales need not be restricted to blues music, they can also work well over other sequences which do not have more than one key centre (e.g. I Got Rhythm A section) – depending on stylistic context.

Boogie Bass

Many rock and roll tunes are based on a 12 bar sequence, often with a typical bass line derived from a boogie-woogie piano left hand (ex 12k). A good way to become familiar with blues changes is to practise this in all keys.

jazz theory

ex 12k: Note the IIm7-V7 progression instead of V7 in the second chorus.

Improvising blues riffs

With a basic blues sequence it is relatively easy for an ensemble to improvise a riff or head arrangement. This was quite common among swing bands of the 30’s. Many early Count Basie arrangements were improvised.

The easiest way is to imagine piano voicings where chords are inverted to keep the top voice around the same pitch (ex 12l). Add 6ths or 7ths where necessary to create 4 note chords.

jazz theory

ex 12l: Typical blues horn riff.

Note the melodic alternation between major and minor 3rd. The major 3rd of the tonic drops to the minor 3rd (7th of the IV chord) and back again. It does not take long for each member of an improvising section to remember his/her notes on a riff such as this, at which point it is easy for the leader to suggest another riff (rhythmic pattern) which everyone can play using the same harmony notes. This principle applies whether creating head arrangements for horns, voices, strings or whatever.
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