In literature, humor can be employed in numerous ways. With the basic intention to cause the reader to laugh or smile, humor generally depends on the reader's recognition of some attribute of a character or situation that is fundamentally true but is misunderstood by another character.
Jane Austen deploys numerous types of humorous devices throughout the novel, but she also constantly reminds the reader of the serious underlying themes. The exaggerated behavior of many characters—along with the witty verbal exchanges, especially between Elizabeth Bennet and Mr. Darcy—combined with the author's wry, ironic tone and style to create a humorous effect.
Lizzie Bennet has a love of words that she has acquired from her bookish father, but she often does not see how her words could wound another person. In her initial interactions with Mr. Darcy, she enjoys teasing him as she might do with any of her friends. While their exchanges are humorous, it is clear that Lizzie is enjoying herself at another's expense.
This inappropriate use of humor is compounded in Lizzie's reaction to her friend Charlotte's engagement. Seeing herself as superior to Mr. Collins—in part because he has absolutely no sense of humor—Lizzie has declined his proposal, only to learn that Charlotte has accepted him. In this exchange, Austen uses humor to make a point about kindness and empathy, as Lizzie hurts her friend's feelings by calling Collins "ridiculous."
Throughout the novel as well, Austen makes it clear that humor has its place, but it should be used in moderation—not to cause others pain.