Early Styles (Musicians Active before 1930)
Early Country Blues
Early Urban Blues
Early Jazz Blues
Kansas City Blues
Later Styles
Post War Jazz Blues
Chicago Blues
Modern Blues (post 1950s)
Blues in conventional pop music
... as "either of those element(s) of the field whose square equals b2 - 4ac". In some fields, some elements have no square roots and some have two; only zero has just one ...