A Philadelphia-based labor and employment attorney by profession, Jonathan Nadler enjoys playing the guitar in his free time. Jon Nadler plays music from a variety of genres, including jazz and blues.
When playing the blues, a guitarist will often utilize the 12-bar progression. This format is the most common in blues music and involves repetitions of the I, IV, and V chords. The I chord is built on the tonic note of the song; a piece in C, for example, will have a C major chord as its I chord. The IV chord is built on the fourth tone of the scale, while the V is built on the fifth tone.
Therefore, in a blues piece in the key of C, the musician will play repetitions of the C, F, and G chords. Each bar features a different chord in the accompaniment. Traditionally, a musician will play the I chord with the first measure and a IV, I, and I chord with each of the next three. The fourth through eighth bars feature IV, IV, I and I chords, in sequence, and the last four bars of the sequence play through the V, IV, I, and V chords. A 12-bar blues song will also often feature an AAB structure, wherein the second four bars are a repetition of the first four and the ninth through 12th bars introduce new lyrics and melody.