Honor
The men in the play are all preoccupied with preserving their sense of honor. When they feel as if someone has insulted their honor or the honor of someone they care about, they defend it vehemently, a contentious dynamic that often results in the challenge of a duel. Lucius O'Trigger is the character who preaches the importance of honor most vehemently, as when he encourages Acres to duel with Beverley, saying, "What the devil signifies right when your honour is concerned? Do you think Achilles, or my little Alexander the Great, ever inquired where the right lay? No, by my soul! they drew their broadswords..."
Women's place in society
Another major theme in the play is the role of women in society. The female characters in the play are not afforded very much control over their own fates. Lydia must forfeit her fortune if she wants to marry for love, Julia must contend with the jealous and insecure suspicions of Faulkland, and Mrs. Malaprop—though she is less sympathetic—is regularly disparaged by the other characters for her age. It would seem that the 18th-century society in which the play is set is not particularly friendly to women's desires. However, the epilogue presents a different perspective on the matter, as the figure of the muse tells the audience that, though it seems that men have all the power, women are in fact the more powerful members of society, because they hold a romantic sway over men. The desirability of women is their principal power, according to the play.
Romance
The play is, ultimately, a romance. While little time is spent examining the love between the various characters, and more often than not they are caught up in quarrels and deceptions, the two young couples, Jack and Lydia and Julia and Faulkland, are at the thematic center of the narrative. The character of Lydia is particularly hung up on the concept of romance as it pertains to fiction. The young noblewoman loves nothing more than to lie around and read romantic sentimental novels, complete with star-crossed lovers and poverty. Her notion of romance is a somewhat naive if pure one, as she believes that true love is about finding someone who is constant even in poverty. In order to prove his steadfast love, Jack Absolute pretends to be poor in his courtship of her.
Deception
The entire plot of the play is built around the deception of Jack Absolute. In the very first scene, we learn that he is pretending to be a lowly ensign in order to win the affection of Lydia Languish, who wants to marry someone poor. While Jack is actually a very wealthy nobleman, he assumes the identity of a poor man in order to win over his beloved. This deception is a central aspect of the narrative arc.
Additionally, Lucy the maid and Faulkland, Jack's friend, pursue their own deceptions. Lucy, as the maid in Mrs. Malaprop's house, is privy to her employers' secrets—both Lydia and Malaprop's. As such, she controls who receives which information when. She brings Lucius O'Trigger's letters for Lydia to Mrs. Malaprop, setting off a whole slew of misunderstandings. She also tells Lydia about Mrs. Malaprop's epistolary affair. Faulkland deceives his lover, Julia, as a way of testing her love. Worried that she does not love him enough, he tells her that he must flee the country, and asks her to come with him, even though this is a patent lie. She agrees to flee the country, but when he informs her that he devised the premise of his exile to test her love, she becomes angry with him, and calls off their engagement.
Language
A running joke in the play is the fact that Mrs. Malaprop often uses language poorly. She substitutes words that do not mean what she thinks they mean into her conversation, which creates a great deal of confusion, and provides comic fodder. Indeed, her misuse of words even led to the coinage of the term "malapropism," which means the unintentional substitution of the wrong word. Malaprop's misuse of language is connected to her pretentious attitude, her lack of self-critique, and her desire to appear learned.
Authoritarianism and Generational Conflict
Making the plot all the more complicated is the tight hold that the members of the older generation have over the decisions of the younger generation. Mrs. Malaprop has told Lydia that she is forbidden from marrying someone poor, and if she disobeys this command she will lose her inheritance. Indeed, it is this ultimatum that leads Lydia to want to rebel and marry someone poor in the first place. Throughout the play, Malaprop disapproves of how inquisitive and independent Lydia is, railing against her penchant for reading and her disobedience.
Anthony Absolute, Jack's father, is also an especially authoritarian parental figure. He decides to pick Jack's bride, and when Jack expresses his resentment of this arrangement, becomes infuriated. Jack's contentment is less important to Anthony than his obedience, and when Jack refuses this arrangement, Anthony yells, "Zounds! sirrah! the lady shall be as ugly as I choose: she shall have a hump on each shoulder; she shall be as crooked as the crescent; her one eye shall roll like the bull's in Cox's Museum; she shall have a skin like a mummy, and the beard of a Jew—she shall be all this, sirrah!—yet I will make you ogle her all day, and sit up all night to write sonnets on her beauty."
Social customs
As a "comedy of manners," the play examines the ways that people, and especially the upper classes, interact and conduct themselves in polite society. Much of the comedy in The Rivals comes from the fact that it is a play about society and social customs, and the ways that the characters are pushed beyond the limits of propriety into more absurd relations. The younger characters must bend to the whims of their parents, and seek to rebel against these strictures in whatever way they can. The servants meddle in their masters' affairs. The play examines the ways that emotion, desire, and the more unruly aspects of the human condition cannot always fit into the strictures of polite society.