One of the qualities that makes Shug such a "natural" in this novel is the fact that Walker did not, by accident, decide to make Shug a blues singer. Clearly, Shug's being a blues singer is central to her character. The blues are the simplest form of jazz — like "Shug" is the simplest form of "sugar." And the word "jazz" itself comes from a West African word meaning, literally, sperm — and, figuratively, life. In turn, Shug brings a sense of life to her audiences with her singing, and, of course, she brings Celie to life.
Shug is full of life on stage, and she seems to live a sweet life, for the most part, because she enjoys shaking and crooning. However, Shug's "blues" dimension is defined by her selfishness — which leads to lonely isolation. In fact, her love for Albert is reduced to a simple, physical longing for him. He has slighted her twice — by not marrying her initially, and again by not marrying her after Annie Julia died. Shug resents Albert's slighting her; she may be a black woman, but she doesn't want to be defined by someone else's sense of a black woman's worth, or in Albert's particular case, by his sense of a black woman's non-worth.
By nature, especially in her singing, Shug is a "changer"; she starts singing the blues, then turns to a fast snappy ragtime tune. Jazz by its very nature is lovely, unpredictable, and improvisational, and Shug is jazzy because she invents rules and cannot be contained. She is originality. She is a changer, and she effects the most change, ultimately, not on herself, but on Celie.
