The Blues originated in the American South after Emancipation, evolving from Spirituals and African American work songs. Common musical techniques included pitch-bending, call-and-response, and the use of "blue" notes.
Blue notes are tones outside the prevailing mode. These were eventually somewhat standardized into the "Blues scale," a hexatonic scale consisting of the tonic, minor third (♭3), subdominant, tritone (♯4), dominant, and minor subtonic (♭7).
C Blues Scale
The Blues became prominent in the early 20th century, and singers like Ma Rainey (1886 - 1939) and Bessie Smith (1894 - 1937) helped to popularize the genre on a wide scale.
Structurally, the Blues tended to fall into "12-bar Blues Form."
I | I | I | I |
IV | IV | I | I |
V | IV | I | I |
St. Louis Blues (Bessie Smith)
Deep Moanin' Blues (Ma Rainey)