Loneliness
While yellow fever poses an immediate physical threat to the residents of Philadelphia, loneliness poses a more crippling emotional threat. Mattie copes better in the moments of danger (nursing her mother, fighting off the thieves) than she does in the moments when she feels utterly alone (such as after the death of her grandfather). Due to the contagious nature of the disease, the epidemic makes it dangerous for individuals to stay in close contact, but the novel makes it clear that human beings need a sense of connection and community in order to be motivated to fight for survival. Loneliness can cause someone to lose the will to fight, and this is more dangerous than any disease.
Fear
When an epidemic starts, society divides into two parts: those who are infected and those who are healthy. To save their lives and prevent the epidemic from further spreading, the second group often becomes quite protective and even heartless. The novel depicts how infected people are kicked out on the streets or left alone to die. When people have only one goal, which is to survive, they act differently, and often cruelly. Especially in an era with limited scientific knowledge, the spread of disease and death often triggered a fear-based response rather than a practical one. However, as the incident with Mattie and her grandfather being stranded in the countryside reveals, fear can lead to even more cruel and dangerous circumstances.
Friendship
Friendship helps Mattie to survive the epidemic, both literally and emotionally. Her friendship with Nathaniel gives Mattie something to hope for and something to imagine enjoying after the epidemic is over. Even though they can only communicate in small ways, Nathaniel shows his loyalty to Mattie through gestures like dropping flowers from the window. By keeping the friendship alive, he helps to keep Mattie motivated and hopeful. Meanwhile, Mattie and Eliza's friendship sustains Mattie in more practical ways. Eliza gives Mattie a place to stay, and a sense of belonging when Mattie has become totally isolated. Later, Mattie cements the friendship by making Eliza her business partner.
Courage
Mattie is required to show courage in a variety of circumstances throughout the novel. She has to have the courage to nurse her mother, find food and water for herself and her grandfather, survive in a desolate city, chase off the thieves, and find the strength to nurse the sick children. Mattie also has to show courage by fighting yellow fever when she falls ill. In all of these circumstances, Mattie finds a strength she did not know she possessed, but she also still struggles with fear, exhaustion, and despair. Throughout the novel, Anderson tells the story of a character for which courage means rising above these feelings, although she is always human enough to feel them.
The mother-daughter bond
At the beginning of the novel, Mattie and her mother have a somewhat tense relationship. They have different values and different hopes for Mattie's future. However, once Mattie's mother falls sick and they are separated for much of the novel, Mattie gains a new perspective. She realizes how much she loves her mother and how much she has learned from her. Without the skills her mother has given her, Mattie would likely have been unable to survive the challenging circumstances she is faced with. As Mattie takes on more responsibilities, she also realizes how hard her mother has been working all these years. When mother and daughter reunite at the end of the novel, they have a loving and appreciative new relationship.
Independence
At the start of the novel, Mattie longs for more independence, as she wants the freedom to make her own decisions and do what she wants. After she loses contact with her mother and eventually loses her grandfather as well, Mattie gains independence but also realizes the high price she has to pay. Once she is actually on her own and has to figure out how to survive, Mattie realizes how exhausting and lonely it can be to be totally on one's own. By the end of the novel, Mattie has achieved a healthy balance of independence and community in her life.
Social responsibility
Social responsibility is a key point of democracy and harmonious coexistence of all members of society. It is also a set of obligations and rules to follow. This story depicts a perfect example of social responsibility. The members of the Free African Society don’t turn their backs to the poor and needy and even risk their own lives trying to help others. In spite of the fact that memories of slavery and horrible treatment still torment the members, they act civilly and kindly. Unlike many representatives of the upper class of the city, they don’t have a lot of money or people to help, but they still do this. Throughout the novel, Mattie's sense of social responsibility matures through interactions with mentors like Eliza and Mrs. Bowles, and she gradually develops into a young woman who cares deeply about others and her role in the community. More generally, a sense of social responsibility has been correlated to the city of Philadelphia eventually making a recovery from the worst impacts of the disease: "After the initial panic, many Philadelphians, as individuals and in groups, dedicated themselves to helping their neighbors... Moved by their conscience and sense of duty, a number of common citizens created or restored civic organizations to help the city" (Smith, pg. 187).