Francie is the central character. Her personality sets the tone for much of the novel. As a young girl, she is bright, keenly observant, and a dreamer. Her family's poverty cannot overshadow the joy she finds in small material pleasures—the neighborhood stores, Flossie Gaddis's dresses, "sheeny" pickles, the Nolan's piano, the conch shell that sits in the living room. She watches and sees everything from her perch on the fire escape or her make-do bed in the front room. Of all the characters in the novel, she is most loyal to Brooklyn and her neighborhood in Williamsburg, and we consistently experiences this place through her consciousness. While Francie does inherit Katie's strength of mind and purpose, she also remains sensitive. As Katie says, she remembers things—the old man's ugly feet, or Joanna's stoning in the street. The reader experiences a vicarious sensitivity for the lives of poor folk through Francie's observations and memories.
Francie's introspective nature leaves her without many friends or companions. This same quality keeps her open and sensitive to her community. The author can establish a sense of place through Francie, because Francie is constantly aware of her surroundings, and wishes to experience even more. She sits on the curb telling herself stories, or watches people from her apartment, or reads.
A Tree Grows in Brooklyn tells the story of Francie's coming of age, and subsequently, her fall from innocence. Growing up, however, does not mean that she becomes jaded by the world. In fact, she learns to value it all the more. Ironically, when America enters the war for the first time, Francie experiences an affirmation of life—she realizes she has to live every minute of every hour the best she can. Indeed, this scene could stand in for the way Francie experiences her coming of age. She realizes on her date with Lee that happiness is not a faraway experience, but the little things in life that people often overlook. The author reaffirms over and over again that Francie is part her father , part her mother. Like her father, she can appreciate beauty. At the same time, she grows more like her mother; when Francie and Katie have differences, it is usually because Francie has learned from her mother to stand up for what she thinks is right. Francie recognizes that Katie favors Neeley and for this reason, Francie consistently tries to win her mother's affections; still, she and Katie are so similar that they never grow as close as Neeley and Katie.
By the end of the book, Francie has a more complex view of her world, but never betrays her home and background. Unlike the nurse administering vaccinations, Francie will never "forget" the people and life she leaves behind.
Like all Rommely women, Katie came "made out of thin invisible steel." The daughter of Austrian immigrants, Katie is hardworking and proud. A life filled with poverty and children has made her hard and detached, and has catalyzed her survivor instinct. While Johnny succumbs to hardship, Katie perseveres, and this is a defining characterization for each of them. Hard times only make her fight harder, and in the end, her children's success makes her struggle worthwhile. Although she changes little throughout the novel, she is softer before the birth of her children. She is romantic enough to fall in love with Johnny, and marry him, all because he could sing and dance. By the time Neeley is born, Katie loses all softness, knowing that she can depend on only herself to provide for her family.
Katie is symbolic of lower-class women in urban America at the turn of the century. She is a second generation American, and reflects the values of an immigrant background. She functions in the novel as a symbol of what the American dream can be. When Mary Rommely gives Katie advice at the beginning of the novel about how she should raise her children, the reader realizes that Katie is the means by which her children will live better lives than their parents.
Although Katie is a valiant character, the novel does not value one parent over the other: both have strengths and weaknesses. Katie never sees any of Francie's writing, for instance; she does not figure out a way for Francie to go to an enchanting school; she brushes her fears aside. Still, Katie provides the means by which Francie and Neeley survive.
Although Katie prefers Neeley to Francie, she loves both her children fiercely. She will make any sacrifice so that they may have an education. Every time a penny goes into the tin-can bank, it is because Katie gives up a little heat, or a little food. Katie worries sometimes that her children are too protected—that they see romance in a mean life, and that without life's cruel truths they will not fight to get out of their poverty. Education, she believes, will cure her children of poverty and meanness. Katie refuses charity in all its forms, teaching her children to grow up with dignity.
Johnny is perhaps the most static character in the book, consistently both weak and romantic. He resorts to drinking to escape a life of hardship. While having two children only makes Katie stronger, Johnny responds by giving up on life. While Johnny's impractical nature makes him worthless as a money-maker, it also makes him an endearing romantic. It is Johnny who brings joy and beauty to Francie and her family. He is handsome and talented; his penchant for singing and music is one of his most cherished legacies. Passionate and loving, Johnny charm captures Francie's heart even if he isn't a model of the conventional good father.
Johnny represents the American dream gone wrong. While Katie survives, Johnny's life of poverty only propels him into a downward spiral. He has a sense of who he could be, what he could have done, and this is his tragedy. He once dreamed of being a real singer on a stage; in reality, Katie cannot even count on his sporadic stints as a singing-waiter. In fact, he often causes the family to lose money; his drinking binge results in their move, for instance. Johnny is also just plain clownish, running into one blunder after another. The moral value system in the novel is in part produced through Johnny's character. Johnny represents a character who no one will reform or moralize. As Sissy says, "we're all something." Johnny's faults do not outweigh his good qualities, and the most admirable characters in the book do not try to save him, but instead, accept him as he is.
Sissy's role in the novel symbolizes the system of values that the book espouses. Despite her tendency toward promiscuity, Sissy remains steadfastly understanding and loving to every person who knows her. The way other characters view her demonstrates the novel's resistance to a conventional way of judging her. She is a well-loved character, despite her reputation with men. Her sisters cannot help but forgive her blunders and sexual exploits, and Francie adores her. The author suggests that her weakness with men is actually a result of her loving personality—she wants to give as much as she can, whether it is to a lover or her family. The novel holds her up as an example of a "good" person; it resists condemning her as the result of one weakness. In fact, the religious themes in the novel also point toward this idea; Katie thinks at one point that God will have to take into account Sissy's goodness when Sissy's soul is wandering through purgatory. This book, through Sissy, is challenging a traditional religious idea of judgment. It is also subtly suggesting that one think of women's sexuality in a more tolerant way.
Sissy and Johnny are similar characters in many ways: both have a weakness, and both have extraordinary qualities that redeem them. Although Sissy is one of the most dynamic characters in the book—changing from a promiscuous woman to a stable mother and wife—the reader should not view this change as a moralizing process. That is, the novel does not value one version of Sissy over the other. Her own desire for a child drives her ultimately to a more stable relationship, but the novel does not seek to correct or moralize her character. Francie, who as the protagonist oftentimes defines the values of the book, actually misses the old Sissy—the one who wore perfume, and had a beautiful, thin figure to attract men. Like Johnny, Sissy's fault is just that—a fault. It does not pervade her whole character. Francie loves both Johnny and Sissy passionately; this, too, is a testament to their goodness.