Themes are the fundamental and often universal ideas explored in a literary work.

Gothic novels

Most literary critics refer to Northanger Abbey as Jane Austen's "Gothic parody" because it satirizes the form and conventions of the Gothic novels that were popular during the time when Austen wrote Northanger Abbey. In particular, Austen is said to have targeted Anne Radcliffe, the author of gothic novels such as A Sicilian Romance (1790), The Romance of the Forest (1791), and The Mysteries of Udolpho (1794). Catherine reads Udolpho during her time at Bath, and it is implied that she has read similar novels before, and Isabella has a library of other Gothic novels that the women plan to read once Catherine has finished Udolpho.

Gothic novels and their conventions occur throughout the novel. On the ride from Bath to Northanger Abbey, Henry invents a humorous hypothetical story about Catherine's first night in Bath, making subtle references to several different Gothic novels, most of which were well-known at the time (consult an annotated edition of Northanger Abbey for a list of the references and the works they come from).

Aside from Henry's parody of gothic novels on the way to Northanger Abbey, two other sequences poke fun at the genre. In once, Catherine unlocks the mysterious cabinet, expecting it to contain something horrible, and finds only laundry bills. In another, Catherine imagines that the General is a wife-murderer and goes to investigate the late Mrs. Tilney's bedroom. When Henry catches her at this task and scolds her, it is not amusing, as is Catherine's discovery of the laundry bills. We feel sympathy for Catherine, who is terribly embarrassed in front of Henry. In the scenes leading up to the confrontation with Henry, it is almost disturbing to read of Catherine's paranoid assumptions that everything the General does stems from a guilty conscience. Catherine becomes almost unhinged by her own imagination. Although the actual crime turns out to be nonexistent, Austen captures some of the psychological tension typical of Gothic novels by chronicling Catherine's delusions. So although she parodies the gothic genre, Austen also makes use of some of its techniques. Some of the novel has nothing to do with Gothic novels and conventions. The first half of Northanger Abbey takes place entirely at the resort town of Bath, and has nothing to do with Gothic novels. This first half resembles Emma or Mansfield Park more than it does The Mysteries of Udolpho.

Youth

Northanger Abbey is concerned with young people and their feelings. Heroines in other Austen novels—Elizabeth Bennett in Pride and Prejudice and Emma Woodhouse in Emma, for example—are a little older than Catherine, and are not as naïveté as she. Northanger Abbey portrays Catherine in situations common to teenagers: she faces peer pressure when James, Isabella and John urge her to join them on their carriage trips, for example, and must contend with the bullying John Thorpe. Austen plays the youthful Catherine against the older, more experienced Henry Tilney. There are several instances in which the adults comment on the young people, either chuckling at their behavior or criticizing it. Many readers can sympathize with Catherine once she returns home and immediately becomes sulky and obstinate with her parents—particularly her mother, who starts gently nagging her daughter right away.