Social class and class ambiguity become obstacles to true love in the novel. One example—the chief example—is the love Catherine and Heathcliff share. Catherine would like to marry Heathcliff but feels he has been too degraded by Hindley, who has reduced him to the level of farmhand and servant. Because she knows marrying him would reduce her to his class, she decides to marry Linton with the idea he will help Heathcliff. Social class also comes into play with the young Cathy and Hareton in the second generation. Heathcliff degrades Hareton to get revenge on Hindley, leaving Hareton illiterate and with rude manners, not a fit husband for Cathy. However, in a happier ending, the two are able to transcend their class differences.
Heathcliff is an example of class ambiguity. He is first raised as a member of the Earnshaw family, with the privilege that entails, then degraded to a servant status, and then comes back a gentleman, with a mysterious gap in his past. Because he presents as a gentleman, Isabella feels it is safe to marry him. In this case, she is deceived. Heathcliff is no gentleman, and his desire to be cruel and abusive interferes with any possibility of the two having a decent relationship.
Nelly Dean is another example of class interfering with true love. Because she is a servant, she has to put up with Catherine's moods and temper. She gets back at her mistress passive-aggressively, as a servant would. For example, she doesn't tell Catherine that Heathcliff is listening to her talking about loving Heathcliff.
Linton's upperclass status as master of the Thrushcross Grange also thwarts love, as he uses his power to separate Catherine and Heathcliff, an act that throws Catherine into a frenzy that makes her ill and ultimately kills her.