Symbols other than the music are also found in the story. Sonny's self-destructive tendencies, shown by his drug use, represent the entire generation of young black men during this time who were aimlessly wandering through life filled with rage.
Another symbol is found when Sonny and his brother rediscover their love for one another. This symbolizes the need we have as human beings to reconnect with others in order to establish unity and a sense of community. It is difficult to find that unity in Harlem since it is the battleground between good and evil.
Water, in the form of sweat and ice, also becomes a symbol. Sonny gets addicted to heroin because he's unable to express the rage and pain he feels inside. He feels cold inside. At the end of his performance, Sonny is soaking wet with sweat because he's been able to finally express his pain.
Sonny's brother, the narrator, describes how he feels when he finds out Sonny has been arrested for the possession and sale of heroin.
"I was scared, scared for Sonny. He became real to me again. A great block of ice got settled in my belly and kept melting there slowly all day long, while I taught my classes algebra. It was a special kind of ice. It kept melting, sending trickles of ice water all up and down my veins, but it never got less. Sometimes it hardened and seemed to expand until I felt my guts were going to come spilling out or that I was going to choke or scream."
The ice is nature's attempts to numb the terrible shock and pain of learning about Sonny's arrest, and the fear the narrator feels for his brother's future. All of his fears for Sonny are locked inside of him as ice. His "warmth" on the outside is seen in the form of sweat. When the narrator feels it, he freezes it into ice so he won't be overwhelmed by his feelings.
Some of these symbols are found in enotes, but some of them I had in my notes from several years ago. Since I'm unsure of where these came from, I'm unable to document a source for them.
“In "Sonny's Blues," Baldwin uses the image from the book of Isaiah of the "cup of trembling" to symbolize the suffering and trouble that Sonny has experienced in his life. At the end of the story, while Sonny is playing the piano, Sonny's brother watches a barmaid bring a glass of Scotch and milk to the piano, which "glowed and shook above my brother's head like the very cup of trembling." As Sonny plays, the cup reminds his brother of all of the suffering that both he and Sonny have endured. His brother finally understands that it is through music that Sonny is able to turn his suffering into something worthwhile.”
Jazz is symbolic of Sonny's need for freedom and to express feelings that he otherwise might have trouble voicing.
Jazz is also symbolic of the relationship of the two brothers, the older of whom, (the unnamed narrator of Sonny's story), does not understand the "language" of jazz which Sonny wants to use to communicate. As the narrator's own understanding of jazz grows, so too does his relationship with Sonny.