Based on Negro works songs. Early blues singers were wandering Negro minstrels: sang blues and accompanied themselves on guitar.
Lyrics were personal.
Three lines – first line repeated, concluding phrase for third line.
After each line the singer could improvise a fill-in phrase on guitar before the next line.
Original form was loose, i.e. three phrases were uneven in length.
Once Blues was an established form in New Orleans jazz, a 12-bar structure (i.e. 3 phrases of 4 bars) became the norm. 8 and…