So Long a Letter is author Mariama Bâ's semi-autobiographical account of her strained marital relations and subsequent life reflections in twentieth-century Senegal. In the story, the main character, Ramatoulaye, loses her husband Modou to a heart attack and uses the mourning period to write a series of letters to her best friend Aissatou, who lives in the US. Similarly, Aissatou is estranged from her former husband, Mawdo, who still lives in Senegal.

Modou and Mawdo have a great many similarities. Both were Senegalese men inculcated in the traditions of post-colonial French North Africa and both were professionals. Modou was a union organizer, respected, and fiercely immersed in his nation's politics, while Mawdo was a doctor and member of the country's noble class.

Both men initially fell deeply and passionately in love with their respective wives despite familial and/or societal opposition. Ramatoulaye and Modou wed despite objections from Ramatoulaye's parents, and Aissatou and Mawdo marry despite class differences and protestations from Mawdo's mother.

Unfortunately, both Modou and Mawdo have wandering eyes and act upon their lusts; however, this is where their differences become most apparent. Mawdo is easily tricked into marrying his second cousin, doing so reluctantly but still professing his undying love for Aissatou. And even after Aissatou leaves him, he remains a loyal friend and confidant to Ramatoulaye.

Modou, on the other hand, finds it far easier to sacrifice his faithfulness and devotion to Ramatoulaye. His love for her (and hers for him) seems to wane with age, and he eventually pursues his own daughter's young friend, Binetou. He eventually marries her despite the fact that she's just 17, abandoning both Ramatoulaye and their children for her. Despite similar positions in society, Modou's character seems far inferior to Mawdo's.