The 12-bar blues (or blues changes) is one of the most prominent chord progressions in popular music. The blues progression has a distinctive form in lyrics, phrase, chord structure, and duration. In its basic form, it is predominantly based on the I, IV, and V chords of a key. Mastery of the blues and rhythm changes are "critical elements for building a jazz repertoire". Background The blues originated from a combination of work songs, spirituals, and early southern country music. The music was passed down through oral tradition. It was first written down by W. C. Handy, an African American composer and band leader. Its popularity led to the creation of "race records" and the popularity of blues singers like Bessie Smith and Ma Rainy. The style of music heard on race records was later called "rhythm and blues" (R & B). As the music became more popular, more people wanted to perform it. General patterns that existed in the blues were formalized, one of these being the 12-bar blues. Basic progression The basic progression for a 12-bar blues may be represented in several ways. It is shown in its simplest form, without the common "quick change", turnarounds, or seventh chords. For variations, see the following section. Chord notation in the key of C: {|class="wikitable" style="text-align:center; width:130px;" |width=25%|C |width=25%|C |width=25%|C |width=25%|C |- |width=25%|F |width=25%|F |width=25%|C |width=25%|C |- |width=25%|G |width=25%|G |width=25%|C |width=25%|C |- |} Functional notationchords are represented by T to indicate the tonic, S for the subdominant, and D for the dominant: {|class="wikitable" style="text-align:center; width:130px;" |width=25%|T |width=25%|T |width=25%|T |width=25%|T |- |width=25%|S |width=25%|S |width=25%|T |width=25%|T |- |width=25%|D |width=25%|D |width=25%|T |width=25%|T |- |} Roman numeral notationI represents the tonic, IV the sub-dominant, and V the dominant: {|class="wikitable" style="text-align:center; width:130px;" |width=25%|I |width=25%|I |width=25%|I |width=25%|I |- |width=25%|IV |width=25%|IV |width=25%|I |width=25%|I |- |width=25%|V |width=25%|V |width=25%|I |width=25%|I |- |} Variations Shuffle blues In the original form, the dominant chord continued through the tenth bar; later on, the V–IV–I–I "shuffle blues" pattern became standard in the third set of four bars: {|class="wikitable" style="text-align:center; width:130px;" |width=25%|I |width=25%|I |width=25%|I |width=25%|I |- |width=25%|IV |width=25%|IV |width=25%|I |width=25%|I |- |width=25%|V |width=25%|IV |width=25%|I |width=25%|I |- |} Quick to four The common quick-change, quick to four, or quick four variation uses the subdominant or IV chord in the second bar. {|class="wikitable" style="text-align:center; width:130px;" |width=25%|I |width=25%|IV |width=25%|I |width=25%|I |- |width=25%|IV |width=25%|IV |width=25%|I |width=25%|I |- |width=25%|V |width=25%|V |width=25%|I |width=25%|I |- |} Seventh chords Seventh chords are