Definition of Dramatic Irony
Catherine is confiding in Nelly that she has accepted Edgar's marriage proposal, yet she's conflicted because she also loves Heathcliff—whom she could never marry:
It would degrade me to marry Heathcliff, now; so he shall never know how I love him; and that, not because he’s handsome, Nelly, but because he’s more myself than I am.
When Isabella believes that she has fallen in love with Heathcliff, Catherine and Nelly try to warn Isabella about Heathcliff's true nature, but she doesn't heed them. Catherine uses nature imagery to convey that Isabella would be completely at Heathcliff's mercy.
Unlock with LitCharts A+"Tell her what Heathcliff is—an unreclaimed creature, without refinement—without cultivation; an arid wilderness of furze and whinstone. I'd as soon put that little canary into the park on a winter's day as recommend you to bestow your heart on him! [...] [H]e'd crush you, like a sparrow's egg, Isabella, if he found you a troublesome charge."
Cathy makes fun of Hareton for trying to teach himself to read. Readers know that Hareton has been struggling to learn to read—and choosing to recite Cathy's favorite passages—in order to impress her and win her affection, but Cathy ironically attributes his efforts to mockery.
Unlock with LitCharts A+'[...] he has no right to appropriate what is mine, and make it ridiculous to me with his vile mistakes and mis-pronunciations! Those books, both prose and verse, were consecrated to me by other associations, and I hate to have them debased and profaned in his mouth! Besides, of all, he has selected my favourite pieces that I love the most to repeat, as if out of deliberate malice!’