In Emily Brontë's Wuthering Heights, the theme of passion vs. social conventions is particularly expressed in Catherine and Heathcliff's relationship.
As children, Heathcliff and Catherine once explore the neighboring estate belonging to the Lintons, Thrushcross Grange, where Catherine is attacked by a dog. She spends six weeks recovering from the attack on the estate, where she is trained to be a lady. Her escapade at Thrushcross Grange also brings her close to Edgar Linton, who later proposes to her. Due to social convention, Catherine feels compelled to accept Edgar's proposal, despite her love for Heathcliff. Catherine is a gentleman's daughter, while Edgar is a gentleman; their marriage would be one of equal social standing, and Edgar would be able to provide well for Catherine. In contrast, Heathcliff is merely an orphan who is treated as a servant by Catherine's brother Hindley, and Catherine knows that, due to social convention, it would be considered beneath her to marry Heathcliff, as she explains to Nelle in the following:
... and if the wicked man in there [Hindley] had not brought Heathcliff so low, I shouldn't have thought of [marrying Edgar]. It would degrade me to marry Heathcliff now; so he shall never know how I love him. (Ch. 9)
Yet passions and not just social conventions drive the actions in the novel. Hence, when Heathcliff overhears Catherine declare her love for him yet say she will marry Edgar because Hindley has brought Heathcliff "so low," Heathcliff vows revenge on Hindley, and it's this vow of revenge that leads to all of the sorrows in the rest of the novel.