Chord progression
12-bar blues progression
Twelve bars, three chords, endless music. The form behind blues, early rock and roll and a good part of jazz.
I7–IV7–V7 in all 12 keys
The three chords of the blues in every key. The play button runs the full twelve bars.
Why I7–IV7–V7 works
The form is three lines of four bars. The first line stays on I, the second visits IV and returns, the third climbs to V, steps down to IV and comes home, with a last bar of V that turns the music round to the start. All three chords are dominant sevenths, which gives the blues its gritty, unresolved sound.
This is the basic form, without the "quick change": four bars of I7, two of IV7, two of I7, then V7, IV7, I7 and V7. Count the bars out loud the first few times; losing your place is the most common blues mistake.
How to practise it
Play a shuffle rhythm, four beats per bar, around 80 BPM. Then try the "quick change": IV7 in bar two, back to I7 in bar three. In E and A the guitar shapes are open and easy.
Use the metronome: start around 70–80 BPM with two or four beats per chord, and change chords exactly on the first beat. When the changes are clean, raise the tempo in small steps and try the same pattern in two or three other keys from the table.
Choosing a key
The numerals stay the same in every key, which is the point of learning I7–IV7–V7 as a pattern rather than as a list of chords. Play it in C until it is comfortable, then pick a row from the table that suits your voice. Guitarists can use a capo to keep the easy open shapes while the music sounds higher.
Variations
Jazz blues adds a ii–V in bars nine and ten, and minor blues uses i, iv and V. An 8-bar and a 16-bar blues exist too, built on the same three chords.