The 12 bar blues is one of the most popular chord progressions in music. Originating from work songs and spiritual hymns, the blues has been around since the early 1900s.
Workers would often share the blues singing catchy melodies with powerful lyrics. It was such an effective canvas for compelling storytelling. So much so, that it became an infectious musical form. Everyone wanted to learn and perform the blues. It wasn’t long before it became a staple across many genres like jazz, folk, and rock.
If you know basic chords and chord progressions, picking up the blues is pretty easy. In this article I’ll break down what the 12 bar blues is, and the different ways to interpret it.
What is the 12 bar blues?
The 12 bar blues is a piece of music that exists within 12 bars of music in common time. It has a distinct harmonic structure that you can't miss. Melodies and lyrics often exist along with the harmony. The different melodies of the blues often distinguish different pieces of music.
The different melodies of the blues often distinguish different pieces of music.
A 12 bar blues divides into three four bar segments. In its simplest form, it’ll contain the tonic, subdominant and dominant chords. In the key of C, this would be C major, F major and G major.
The first segment contains four bars of C major. The second segment contains two bars of F major and two bars of C major. Finally, the third segment brings in the G major chord for one bar followed by the F major for one bar. It finishes off with two bars of C major.
12 bar blues chords
The simplest form of the 12 bar blues contains simple major triads. The chord type is often altered depending on the genre of music.
In rock music you’ll find that the blues centers around the key of E major. You'll hear guitarists using power chords, which translates to the guitar perfectly. In jazz music it’s common to find the blues in the keys of F major or Bb major using seventh chords and minor chords. Therefore, these keys and chords are well suited for wind instruments.
1. Seventh Chords
Replacing seventh chords in place of triads in a 12 bar blues is as simple as adding a flat seventh to each major triad. This makes a dominant seventh chord.
The jazz blues is one of a kind. It’s not common to find tunes that have only dominant seventh chords throughout.
2. Minor Chords
Replacing minor chords in place of major triads in a 12 bar blues makes a ‘minor blues’. It’s important to note that not every chord is replaced by a minor chord.
In the key of C, replace C major and F major with C minor and F minor. You’ll find all the chords to be minor seventh chords as well.
In the third segment of a minor blues, you’ll find a VI dominant chord followed by a V dominant chord. They replace the V and IV I used in the major blues.
While chord qualities can swap out on the basic 12 bar blues form, you can also make chord substitutions.
1. Quick IV Chord
The quick IV chord happens in the first segment in the second bar. Replace the I chord with a IV chord, which immediately goes back to the I chord. This works well when the melody of the blues highlights the chord tones of the IV chord.
The turnaround is a jazz centric term for turning around the end of the song form back to the beginning. Harmonically, the turnaround signals a complete sounding cadence that consists of a I-vi-ii-V chord progression.
The turnaround is a classic ending that isn’t restricted to the blues. You’ll find the turnaround in most classic jazz songs. Furthermore, turnarounds often feature chord substitutions.
3. Secondary dominants
Secondary dominants are chords from outside the home key that relate to chords in a progression by a V-I relationship. For example, the (V) G chord in the 12 bar blues has the secondary dominant D7. This is notated using roman numerals that say “five of five” (V/V)
Hot Tip: Count up five scale degrees to find any secondary dominant: G-A-B-C-D.
You can precede any secondary dominant with a related ii chord. In the case of (V) G and (V/V) D7, the related ii chord would be (ii/V) A min.
You can precede any secondary dominant with a related ii chord.
In the blues, you’ll find that secondary dominant chords and related two chords can exist almost anywhere in the form. The most common places that contain secondary dominants are in the 4th measure, as well as the 11th measure in the turnaround. To make it even more jazzy, replace the first chord in the third segment with a (ii) D minor preceding with its secondary dominant, and a (V) G7 chord before the turnaround.
4. Tritone substitution
It’s common to find tritone substitution paired with secondary dominants. Because the blues often uses all seventh chords, the possibilities are endless.
Tritone substitution means to substitute a dominant chord with another dominant chord a tritone away. To find a tritone, count up or down six semitones from the root of the chord that's changing. The substitution contains the same third and seventh, with the root changing a tritone. For example, replace the C7 in the fourth bar of the first segment with an F#7. You can also replace the A7 in the turnaround with an Eb7.
To take it even further, you can place a secondary dominant of the original A7 in the turnaround before the Eb7, which is E7. This gives a nice chromatic movement in the bass and adds more color to the turnaround.
A brief history of the 12 bar blues
Now that we've looked at some of the theory behind the 12 bar blues—let's explore a little bit of its rich history and the reasons why the chord progression and form is so popular.
While tons of chord substitutions and harmonic alterations are possible in the blues, the main elements that led to its popularity are the melody and lyrics. The blues is so simple to sing along with, and easy to memorize. The recurring chord progression made it approachable for any musician to play along on guitar and harmonica. In addition, it also made soloing and improvisation universally understood—often using the blues scale.
The blues is so simple to sing along with, and easy to memorize.
The earliest form of the blues was called the Delta blues, or country blues. One solo singer would carry the tune, while playing the harmonica or bottle neck slide guitar.
As the blues progressed, it became adopted by jazz, R&B and eventually rock and pop artists. Jazz artists like Miles Davis and Charlie Parker took the blues and altered it in many different ways to make it their own.
Rock guitarists Stevie Ray Vaughn and B.B. King’s whole careers were shaped around the blues. As it continued to develop through the 80’s and 90’s until now, it influenced countless artists and genres of music.
The 12 bar blues is truly a timeless genre. The origin and development of the blues demonstrates the power of music, and how it brings people together.