The twelve bar blues

A foundational song form that is really a huge variety of song forms

The twelve-bar form is a central convention of the blues. It’s so closely associated with the blues generally that jazz musicians use the term “a blues” to mean any tune using the twelve-bar form. However, it is surprisingly difficult to define what the twelve-bar blues actually is. That’s because there is no such thing as “the” twelve bar blues. Instead, there is a vast constellation of blues song forms that share some general structural features in common. In this post, I won’t even begin to list every variant; I’ll just give some representative examples. For the real truth about this music, you need to consult the music itself.

Twelve bar blues famously uses the I, IV and V chords. If you are unfamiliar with Roman numeral notation, it’s easier than you would think. Pick any key, say, C. The I chord will be C. Simple! Now think of the C major scale. The IV chord will have its root on the fourth scale degree, F. The V chord will have its root on the fifth scale degree, G. If you are in the key of A, then the I chord is A, the IV chord is D, and the V chord is E. If you are in the key of E-flat, then the I chord is Eb, the IV chord is Ab, and the V chord is Bb.