12-bar blues

Three chords, infinite solos

The blues is a twelve-bar loop of I, IV, and V. It looks simple and it is — which is exactly why it never runs out.

The form

bars 1–4    I  (four bars of home)
bars 5–6    IV (the lift)
bars 7–8    I  (back home)
bars 9–10   V  (the turn)
bars 11–12  I  (land it)

Why it matters

Everything from rock to jazz to hip-hop descends from this loop. If a progression can be played on a porch, it's probably the blues.