Some purists feel that any variations or embellishments of the basic blues pattern changes its quality or validity as a blues song. For instance, if the basic blues chord progression is not used, then the music being played is not the blues. I believe this viewpoint to be a bit wide of the mark, because it places a greater emphasis on blues harmony than melody. The principal blues melodies are, in fact, holler cadences, set to a steady beat and thus turned into dance music and confined to a three-verse rhymed stanza of twelve to sixteen bars. The singer can either repeat the same basic melody for each stanza or improvise a new melody to reflect the changing mood of the lyrics.
Blues rhythm is also very flexible.
Jazz instrumentalists frequently use the chord progression of the twelve-bar blues as a basis for extended improvisations. The twelve or sixteen bar pattern is repeated while new melodies are improvised over it by the soloists. As with the Baroque bassocontinuo, the repeated chord progression provides a foundation for the free flow of such improvised melodic lines. The blues is neither an era in the chronological development of jazz, nor is it actually a particular style of playing or singing jazz. Some feel that the blues is a way to approach music, a philosophy, in a manner of speaking.