In the 1947 play, written by Tennessee Williams, and the 1951 film A Streetcar Named Desire, directed by Elia Kazan, the characters give hints of their back stories through dialogue. But if the audience truly wants to understand and know the backgrounds of the characters, they need only to turn up their sets or listen closely to the music. The music within the play and the movie, as scored by Alex North, gives the audience clues on the desires of each character.
At the end of scene one, Stanley (Marlon Brando) asks Blanche (Vivien Leigh) to confirm she had been married before. On this note polka music begins to play faintly in the background. Whenever her past marriage is brought to her attention, this music begins to play. It is a playful, almost carousel-like tune, invoking Blanches desire to be young again, and go back to the time before her husband's suicide. As soon as she remembers the suicide in her past, a gunshot is heard and the music vanishes and we see the most aware that Blanche will ever truly be.
In the third scene, the music echoes the heightened emotions of the characters, and then slowly brings them back to their normal status. In the play, the music is described as "dissonant brass and piano sounds…the 'blue piano' plays for a brief interval" when Stanley is begging for Stella over the phone. In the film it resembles the play, but differs when it comes to the climatic scene of Stella slowly descending the stairs.
In the play the only music described is a "low-tone clarinet moan." In the film, the music echoes the characters perfectly. The clarinet acts as Stella, a slow rhythm at a low tone. The saxophone notes (I assume) wander in the background, just like Stanley figuring out how to regain his "baby" as well as regain his power over her. As Stella descends the stairs, the piano echoes her footsteps by playing descending scales. The next time we see Stella, she is lying in the bed underneath a saxophone, and symbolizing Stanley is back on top.
In the film Blanche is playing dress up and singing "Paper Moon." The song is a word-for-word vocalization of her desire. "It's only a paper moon/Sailing over a cardboard sea/But it wouldn't be make-believe/If you believed in me." Blanche wants to go back to her past. Her only desire is that everyone else should just accommodate this and let her pretend to be in a time when she was happy. Living with Stanley though, she finds him tearing up her paper moon, and stomping on her cardboard sea.
When Blanche finally does have her breakdown, the music in the film becomes crazy. The staccato notes of the plucked strings give the audience a sense of how everything around Blanche is coming crashing down, one by one, rather than one single drop. The music untangles Blanche's complex nature in her breakdown, allowing viewers to feel for her character, rather than be glad she is finally done annoying Stanley.
The combination of Alex North's excellent composing and Tennessee Williams ability to use single instruments to single out characters makes A Streetcar Named Desire an enjoyable film to watch because one can feel closer to the characters by feeling, through the music, the emotions of each individual.