Arranged Marriage vs. Love
The central conflict in "Marriage is a Private Affair" stems from Nnaemeka's and his father's clashing conceptions of what makes a good marriage. The village-dwelling Okeke stubbornly insists upon the Ibo tradition of arranged marriage, which is orchestrated and agreed upon by the bride and groom's families, often ignoring the wishes of the couple being wed. Nnaemeka, however, values love over tradition, and thus finds a wife who is not Ibo but whom he knows he will be happy with. Nnaemeka's arguments in favor of privileging love over tradition do not sway Okeke: When Nnaemeka protests to his father that he cannot marry Ugoye because he does not love her, Okeke replies, "Nobody said you did. Why should you?" Nnaemeka insists that contemporary ideas around marriage are different than they were when Okeke was young, but Okeke refuses to accept his son's appeal, insisting that nothing about marriage has changed and the only important qualities in a wife are her Christian upbringing and good character. Ultimately, in their clashing views of matrimony, Nnaemeka embodies a modern privileging of emotion over convention while Okeke exemplifies an orthodoxy that gradually loses the battle against feelings.
Obstinacy
Obstinacy—the quality of stubbornly sticking to an opinion in the face of persuasion—is another of the story's major themes. Embodied in Okeke's refusal to accept his son's decision to marry for love, obstinacy enables Okeke to reject every emotional appeal Nnaemeka and Nene make to him over the years. Preferring to disown his son rather than entertain the possibility that he is not entitled to determine who his son marries, Okeke grows to old age alone in his village, becoming so angry when his son is mentioned that villagers learn to keep their mouths shut about the happy couple. Okeke's obstinacy leads him to cut up Nnaemeka and Nene's wedding picture and send it back to the couple as a symbol of his contempt. It is only when Okeke learns that he has grandsons that his obstinacy is shaken. Having successfully hardened his heart to his family, Okeke finally loses the battle against familial affection when he pictures his grandsons standing in the rain, shut out from his home. By the end of the story, Okeke feels remorse for having been so stubborn and unfeeling.
Tradition vs. Modernity
The tensions that arise from the conflict between tradition and modernity is another central theme in "Marriage is a Private Affair." Explored overtly through the conflict between arranged marriage and marrying for love, as well as the juxtaposition between city life and rural life, the theme of tradition vs. modernity also arises within the dynamics of Okeke's village. Despite his obstinate rejection of his son's decision to marry for love, Okeke is considered more modern than his fellow villagers. When other men discuss the option of hiring a herbalist to brew a concoction that could keep Nnaemeka's heart under his father's control, Okeke rejects the idea, as he is "known to be obstinately ahead of his more superstitious neighbours in these matters." However, Okeke is unaware of the hypocrisy of having a steadfast adherence to the tradition of arranged marriage while easily dismissing the concept of traditional medicine. Nene and Nnaemeka also hold a mix of traditional and modern values. While they are willing to disobey Okeke in the matter of love and marriage, they cannot reject him in the way he rejects them, continuing to reach out to him in the tradition of honoring one's elders.
City vs. Village
In "Marriage is a Private Affair," Achebe juxtaposes the differences between city life in Lagos and rural life in an Ibo village. While urbanity is associated with a diversity of backgrounds and viewpoints, the village is associated with tradition, adherence to a singular culture, superstition, religiosity, and a stubborn refusal to change. While Nene represents the city, having lived so long in the "cosmopolitan atmosphere" of Lagos that she is surprised to learn that Nnaemeka's father still believes in arranged marriage, Okeke represents the country, obstinate in his belief in tradition. Regularly traveling between the city and the village, Nnaemeka finds himself torn between his newfound urban identity and his rural origins, feeling allegiance to both his wife and his father. Although Achebe begins the story from Nnaemeka's point of view in the city, the narrative point of view stays in the village after Okeke rejects his son. The shift in perspective immerses the reader in Okeke's stubborn and lonely life apart from family. Alone, Okeke cannot pass on any wisdom or traditions to his grandsons—a state of affairs Okeke comes to regret. In this way, "Marriage is a Private Affair" illustrates how the village's refusal to adapt to the cultural changes brought about in the city leads to a greater divide that will cause the village and its traditions to die out.