As in all of Austen's novels, the subjects of society, status, behavior, and morality are addressed. Northanger Abbey, however, being chronologically the first novel completed by Austen (though revised later in her life), and notably considered a "point of departure" from her other work as a result of the "boldness with which it flaunts its . . . deceptive air of simplicity with broad, bold humour" includes several major themes that are specific to this text. Such themes include:
The intricacies and tedium of high society, particularly partner selection, and the conflicts of marriage for love. When Catherine enters Bath, she is rather unaware of the societal setting she will encounter. The text notes that her mother, also, knew little of high society, which explains why Austen pairs Catherine with the Allens, who are higher ranked in society than she, due to their wealth. Society greatly influences partner selection, especially in Northanger Abbey, as General Tilney, for example, disapproves of Henry and Catherine's love due to their disparity in wealth. General Tilney only accepts Henry and Catherine's marriage after Eleanor Tilney becomes engaged to a wealthy man. Further, Catherine distances herself from John Thorpe, though he is societally deemed a "good" match for her. Rather, Catherine bravely situates love and companionship as more worthy than standing and rank, unlike Isabella, who ends the novel with two broken engagements.
Life lived as if in a Gothic novel (as if life were the same as fiction), filled with danger and intrigue, and the obsession with all things Gothic. Though Austen greatly encourages the reading of novels to her readers, Catherine must learn to separate life from fiction, and rein in her very active imagination. When Catherine accuses General Tilney of murdering or locking up his wife, she is humiliated when it is discovered to be untrue, as Henry chastises her, by saying: "'You had formed a surmise of such horror as I have hardly words to— Dear Miss Morland, consider the dreadful nature of the suspicions you have entertained. What have you been judging from?'" Upon this, Catherine is mortified, and distraught at the notion that Henry would think less of her for her wild assumptions. When reflecting, Catherine identifies that she must separate Gothic novels from her judgement of everyday life. This serves as a major progression in the novel, as it is a sign of Catherine's maturation, and ability to appreciate novels without immediately applying them to her behaviors and thoughts.
The development of the young into thoughtful adulthood, the loss of imagination, innocence and good faith. While Catherine controls her imagination, she simultaneously endures the reality of individuals not behaving in the manner they should. Most prominently, Catherine realizes she is not to rely upon others, such as Isabella, who are negatively influential on her, but to be single-minded and independent. Isabella, regardless of her engagement to James Morland, flirts with Frederick Tilney, breaks her engagement to James, is discarded by Frederick, and causes herself great shame. Catherine began to realize the wrongs of Isabella's influence when the Thorpes cause her to miss her appointment with Henry and Eleanor Tilney early on, but it is not until the shocking wrongdoing against her brother that Catherine entirely separates herself from their friendship, stating that she may never speak to Isabella again, and is not as upset as she thought she would be. As this scene takes place almost immediately after Catherine's lesson about Gothic novels, it is a clear sign of her increasing maturity.
Reading as a valuable tool for personal growth. In one of Austen's narrator's boldest proclamations, the narrator of Northanger Abbey exclaims upon the significance of reading novels, writing: "I will not adopt that ungenerous and impolitic custom so common with novel-writers, of degrading by their contemptuous censure the very performances, to the number of which they are themselves adding—joining with their greatest enemies in bestowing the harshest epithets on such works, and scarcely ever permitting them to be read by their own heroine, who, if she accidentally take up a novel, is sure to turn over its insipid pages with disgust. Alas! If the heroine of one novel be not patronized by the heroine of another, from whom can she expect protection and regard? I cannot approve of it". In this famous moment, Austen's narrator acknowledges the hypocrisy in insulting those who read novels. It is also made clear in this text that those who are considered "good" and well-educated read novels, such as Henry and Eleanor Tilney. John Thorpe, for example, who does not read novels, is the cad of the text. Furthermore, there is a distinction made between Catherine's imagination and childishness that encourages her fantasy of a murderous General Tilney, rather than it being a direct fault of the novel genre.