From beginning to end, Wuthering Heights is a novel full of ghosts and spirits. Dead characters refuse to leave the living alone, and the living accept that the deceased find ways of coming back to haunt them. In a departure from traditional Gothic tales, these hauntings are sometimes welcome. Heathcliff, for instance, repeatedly seeks out visitations from the ghost of his beloved Catherine. He even digs up her grave in order to be closer to her. Brontë uses otherworldly figures to emphasize the ferocity of Heathcliff's and Catherine's love; their connection is so powerful that even death can't stop it.
Pitting nature against civilization, Emily Brontë promotes the Romantic idea that the sublime—the awe-inspiring, almost frightening, beauty of nature—is superior to man-made culture. She makes this point by correlating many of the characters with one side or the other and then squaring them off against each other. For instance, Heathcliff, whose origins are unknown and who roams the moors, is definitely on the nature side, while his rival, the studious Edgar Linton, is in the civilized camp. Other pairings include Hareton Earnshaw vs. Linton Earnshaw; Catherine vs. Isabella; and Hareton vs. Cathy. In all of these cases, Brontë makes one character a bit wild (perhaps by showing them in tune with animals and/or the outdoors and/or their emotions), while portraying the other as somewhat reserved and often prissy or fussy.
But nothing is black and white in Wuthering Heights. Many of the characters exhibit traits from both sides. While Brontë argues that nature is somehow purer, she also lauds civilization, particularly in terms of education. Hareton Earnshaw personifies this combination of nature and civilization: Brontë associates the young orphan with nature (he is a coarse, awkward farm boy) as well as civilization (inspired by his desire for young Cathy, he learns how to read). This mixture of down-to-earth passion and book-centered education make him, arguably, the most sympathetic character in the book.
Wuthering Heights explores a variety of kinds of love. Loves on display in the novel include Heathcliff and Catherine's all-consuming passion for each other, which while noble in its purity is also terribly destructive. In contract, the love between Catherine and Edgar is proper and civilized rather than passionate. Theirs is a love of peace and comfort, a socially acceptable love, but it can't stand in the way of Heathcliff and Catherine's more profound (and more violent) connection.
The love between Cathy and Linton is a grotesque exaggeration of that between Catherine and Edgar. While Catherine always seems just a bit too strong for Edgar, Cathy and Linton's love is founded on Linton's weakness—Linton gets Cathy to love him by playing on her desire to protect and mother him. Finally, there's the love between Cathy and Hareton, which seems to balance the traits of the other loves on display. They have the passion of Catherine and Heathcliff without the destructiveness, and the gentleness shared by Edgar and Catherine without the dullness or inequality in power.
Written when gender roles were far more rigid and defined than they are now, Wuthering Heights examines stereotypes of masculinity and femininity. Emily Brontë constantly contrasts masculinity and femininity, but not all of the comparisons are simple; sometimes boys act like girls and girls act like boys. Edgar Linton and Linton Heathcliff, for instance, are men, but Brontë frequently describes them as having the looks and attributes of women. Likewise, Catherine Earnshaw has many masculine characteristics; even though she is outrageously beautiful, she loves rough, outdoor play and can hold her own in any fight. She is a complex mix of hyper-feminine grace and loveliness and ultra-masculine anger and recklessness. Heathcliff, with his physical and mental toughness, has no such ambiguities—he is exaggeratedly masculine and scorns his wife Isabella for her overblown femininity.
Emily Brontë seems to favor masculinity over femininity, even in her women. In general, she portrays weak, delicate characters with contempt, while she treats strong and rugged characters like Heathcliff, both Catherines, and Hareton, with compassion and admiration, despite their flaws.
Understanding the importance of class in eighteenth- and nineteenth-century Britain is essential to understanding Wuthering Heights. Generally, at the time, people were born into a class and stayed there: if your parents were rich and respected (like Edgar's), you would be, too; if your parents were servants (like Nelly Dean's), you probably would be too. Social mobility—the idea that you can change your class status (usually for the better)—was not commonplace.
In Brontë's novel, however, class distinctions are constantly changing, much to the confusion of the characters. There are two primary examples of this: Heathcliff and Hareton. Because no one knows anything about Heathcliff's background, they all treat him differently. Mr. Earnshaw adopts him and treats him like a son, but the snobby Lintons refuse to socialize with him. When he disappears for a few years and comes back rich, the characters struggle even more over how to approach him—he now has money and land, but many of them still consider him a farm boy. Likewise, Hareton has a hard time gaining respect. The son of Hindley, Hareton should be the heir to Wuthering Heights. With land and standing, he ought to be a gentleman. However, Heathcliff refuses to educate him, and everyone else mostly ignores him, so his manners (a very important indicator of class status) are rough and gruff. Only when young Cathy helps educate him does he achieve the class standing to which he was born.
Nearly all of the action in Wuthering Heights results from one or another character's desire for revenge. The result are cycles of revenge that seem to endlessly repeat. Hindley takes revenge on Heathcliff for taking his place at Wuthering Heights by denying him an education, and in the process separates Heathcliff and Catherine. Heathcliff then takes revenge upon Hindley by, first, dispossessing Hindley of Wuthering Heights and by denying an education to Hareton, Hindley's son. Heathcliff also seeks revenge on Edgar for marrying Catherine by marrying Cathy to Linton.
Yet while Heathcliff's revenge is effective, it seems to bring him little joy. Late in the novel, Cathy sees this, and tells Heathcliff that her revenge on him, no matter how miserable he makes her, is to know that he, Heathcliff, is more miserable. And it is instructive that only when Heathcliff loses his desire for revenge is he able to finally reconnect with Catherine in death, and to allow Cathy and Hareton, who are so similar to Heathcliff and Catherine, to find love and marry.