The twelve-bar blues
The most-used chord pattern in popular music has just three chords, in a fixed order, over twelve bars. Here it is in Roman numerals, one chord per bar:
In the key of C that is C7 – F7 – G7. In G it is G7 – C7 – D7. The same I – IV – V three chords power a huge share of rock, country, jazz and pop.
Variations
- Quick change: bar 2 goes to the IV chord: I IV I I / IV IV I I / V IV I V.
- Turnaround: bar 12 plays V to push back to bar 1; the last chord of a song is usually I.
- Minor blues: the same shape with minor i, iv and a dominant V.
Song forms
Musicians label sections with letters: A for the first idea, B for a contrasting one. Repeats keep the letter; a changed return can be A′. Here are the shapes you will meet most:
| Pattern | Name | What it is |
|---|---|---|
| A A B A | 32-bar song form | Two statements of the main tune, a contrasting middle section (the bridge), then the tune returns. The backbone of jazz standards and Tin Pan Alley songs. |
| A B A B | Verse–chorus form | Verse and chorus alternate. The chorus carries the hook and returns unchanged, while the verse changes its words. |
| A B A | Ternary form | A section, a contrasting B section, then A again: statement, contrast, return. |
| A B | Binary form | Two contrasting sections, often each repeated. The standard shape of baroque dances. |
| A B A C A | Rondo form | The main theme A keeps coming back, with new contrasting sections between. |
| A A A | Strophic form | The same music repeated for each verse, with new words each time. |
Phrases and cadences
Inside a section, music moves in phrases, usually four bars long, like sentences. Phrases end with a cadence: a chord pair that works like punctuation. V → I is a full stop (an authentic cadence); ending on V is a comma (a half cadence); IV → I is the "Amen" (a plagal cadence). Two phrases that ask and answer make an eight-bar section.
How to practise
- Warm-up: blues chords in C, G and F and the four basic forms.
- Working set: blues in other keys; every form.
- Heavy lift: the quick-change blues.
Combine this with Roman numerals, the chord transposer, the blues scale and the Melody and Form program.
Frequently asked questions
What is the 12-bar blues?
A chord pattern of twelve bars: four bars of I, two of IV, two of I, then V, IV, I and V (or I). In the key of C it is C7 four bars, F7 two, C7 two, G7, F7, C7, G7. Thousands of songs use it.
What does AABA mean?
A way of labelling sections: the main tune (A) is played twice, then a contrasting section (B, often called the bridge), then A returns. The classic 32-bar song form has four eight-bar sections.
What is a bridge?
A contrasting section, usually harmonically and melodically different, that leads back to the main material. In AABA it is the B section; in pop songs it often comes after the second chorus.
What is the difference between verse and chorus?
The verse tells the story and changes its words each time. The chorus is the hook: it keeps the same words and tune and is usually the most memorable, highest-energy part.
What is a turnaround?
The last bar or two of a chord sequence, which leads back to the beginning: in the blues, bars 11 and 12 (I – V). It sets up the repeat.