Twelve-bar blues
The standardized chord progression of the blues.
What it means
The twelve-bar blues is a fixed chord progression over twelve bars that underlies a large part of blues and jazz. In its basic form, four bars are on the tonic, two on the subdominant, two on the tonic again, then one bar each of dominant and subdominant, and two closing bars that lead back to the repeat. All three degrees are usually played as seventh chords — a peculiarity that functional harmony cannot explain.
Musical use
The scheme is a model, not a rigid framework: countless variants insert passing chords, alter individual bars, or extend the form. Players improvise over this progression, and its return every twelve bars gives players and listeners a point of orientation. Associated with the scheme is the blues scale with its characteristic notes, which rub against the chords and give the style its colour. In singing, the form often corresponds to a text structure of two identical lines and a third that answers them. The influence of the scheme reaches far beyond blues and jazz.
Performance practice
Learn the form by heart and count the twelve bars along; if you lose the form, you lose everything. Practise accompanying first before you improvise — a secure rhythm section is the prerequisite. Listen a lot and learn phrases from recordings, not from scale exercises. Work on the rhythmic groundwork, because it carries more than the choice of notes. Before you begin, settle with the ensemble which variant is being used, the key, and the number of choruses.
Bear in mind that the form is treated differently in different styles: in older blues, departures from the twelve bars are common and part of the performance, whereas in jazz the form is usually kept strictly. Settle this beforehand when musicians from different backgrounds play together. When accompanying, make sure to make the change to the subdominant in bar five clear, because it articulates the form. Practise the closing turnaround of the last two bars separately, since that is where it is decided whether the next chorus will carry.