Marriage
One of the major themes in the novel is marriage. Because the novel is set in an Islamic country, marriage is seen as being something every woman must do in her life. The main character of the novel gets married as well but the union is not a happy one as she is later replaced by a much younger wife. Thus, Ramatoulaye finds herself in the situation of having to learn how to take care of herself and of her children without the help or presence of a man in her life. For her, marriage does not mean protection; rather, it is a painful experience she has to go through in order to survive. But the failed marriages in this novel are not necessarily perceived as being a negative thing; they are also a way through which a person can grow and better themselves.
Religious tradition
Another theme analyzed in the novel is the idea of Islamic tradition and how it affects a person’s life. While Ramatoulaye is a progressive woman in the sense that she wants freedom and wants to be independent, she still submits to the Islamic laws she is exposed to. Even though her husband took a second wife, Ramatoulaye still feels like it is her duty to take care of his funeral and of everything that has to do with her late husband’s life. This proves that Islam influenced her life greatly and while she prides herself on being a feminist, she still remains governed by the laws she was taught to respect all her life.
Motherhood
Another theme in the novel is the idea of motherhood. In Islam, women are expected to remain pregnant and have as many children as possible. Ramatoulaye, for example, had 12 children with her husband. In her opinion, this should have been enough to make her husband stay by her side, but this proved to be wrong. Despite this, Ramatoulaye still loved her children and did everything she could to make sure that they are well raised and that they have everything they need. For Ramatoulaye, the relationship she had with her children was more important than anything else and she was willing to do everything in her power to keep them safe and to make them happy.
Romantic Love vs. Friendship
Throughout the novel, Ramatoulaye must navigate the love she has for her husband and the love she has for her best friend. Despite the fact that traditionally, both of them should be happily married, both Ramatoulaye and Aissatou find that marriage does not fulfill all of their needs, and that romantic love often proves to be insufficient for living a full life. Over the course of their lives, they learn that their permanent friendship is stronger than their temporary marriages. At the end of the novel, Ramatoulaye is ready to explore happiness through the friendships she's built with others, choosing not to find her fulfillment through a man or a romantic relationship—a significant rebellion.
Education
Education is at the center of most of the character's lives in this novel. Modou and Ramatoulaye meet while in school, as do Aissatou and Ramatoulaye. Ramatoulaye and Aissatou are both teachers and are determined to give their children excellent educations as well. In the text, as well as in mid-20th century Senegal more generally, education is one of the most reliable ways to access social mobility. More than that, education is a way for women to move forward in society and for people who are not considered as "high class" as others, like Aissatou, to gain more sociopolitical power. Finally, education represents a potential for enlightenment, not just for individuals, but for the entire country.
Independence
Multiple parties in the novel deal with fighting for and managing independence. On a national level, So Long a Letter is set in the context of a Senegal which had recently declared independence from France. As Ramatoulaye acknowledges, her generation is a bridge between colonial Senegal and independent Senegal, and all of the political moves mentioned in the novel concern how Senegal must learn how to exist as an independent nation when it is a country constructed through colonial rule. At the same time, characters like Ramatoulaye and Aissatou struggle to find their own personal independence in these tense political and personal contexts, where there is an enormous amount of potential for them, but they are also extremely limited by tradition and their circumstances. But moments like Aissatou deciding to leave Modou, Ramatoulaye deciding to live without a husband, and the situation with the car show how they manage to find their independence despite the odds.
Women's Rights
Touching on several other themes, the question of rights of women in Senegal and greater West Africa dominate this novel. All of the main characters are supposedly in support of women's advancement on a political level, but often, their personal circumstances challenge this advocacy. For Modou and Mawdo, their choices concerning polygamous marriage undermine the power that their wives have, despite their political views, as does Daouda's willingness to marry Ramatoulaye but not to be just her friend. Even Ramatoulaye must struggle with balancing her attachment to women's advancement and her dedication to tradition, such as deciding whether or not to disown Aissatou and how to talk to her daughters about sex.
