The jazzy 12-bar lyric framework of a blues composition is reflected by a standard harmonic progression of 12 bars in a 4/4 time signature. The blues chords associated to a twelve-bar blues are typically a set of three different chords played over a 12-bar scheme. They are labeled by Roman numbers referring to the degrees of the progression. For instance, for a blues in the key of C, C is the tonic chord (I) and F is the subdominant (IV). The last chord is the dominant (V) turnaround, marking the transition to the beginning of the next progression. The lyrics generally end on the last beat of the tenth bar or the first beat of the 11th bar, and the final two bars are given to the instrumentalist as a break; the harmony of this two-bar break, the turnaround, can be extremely complex, sometimes consisting of single notes that defy analysis in terms of chords.
