Which characteristic distinguishes blue music in the late nineteenth century from earlier forms of blues music?

Blue music in the late nineteenth century is distinguished by its incorporation of more structured forms and a greater emphasis on lyrical storytelling compared to earlier blues forms. This period saw the emergence of published sheet music and the influence of African American folk traditions, which blended with popular music styles. Additionally, the use of specific chord progressions and the introduction of the twelve-bar blues format became defining traits during this era, setting it apart from the more improvisational and less formalized earlier styles.