An historic purpose served by blues music was as an outlet for a captive people with no other voice, according to an All About Jazz article on the blues by Ed Kopp. Early versions of the blues, including African tribal music and chants, work songs and spirituals, gave African-American slaves some measure of freedom to comment on their own hardship, work issues and emotional pain.
Another purpose for blues music was to pass on oral traditions and establish cultural connections. A blues song about hard times might begin in the Mississippi Delta, the birthplace of the blues according to Ed Kopp's article, and eventually a similar blues would surface and be sung in Alabama or Georgia.
Besides addressing hardship, work issues and oppression, another purpose of the blues was to connect with emotional issues, particularly the loss and pain of love, according to The Blue Highway article on the blues by Robert M. Baker. When someone suffers heartbreak, he can deal with it on both an intellectual and gut level by literally "crying" or "singing" the blues.
Mississippi Delta blues or traditional blues was one of the first types of blues, according to Ed Kopp. Regional blues, such as St. Louis Blues and Chicago Blues, grew as the music spread across the country---yet, all types of blues must address emotional issues in order to be considered true "blues."