How does the author successfully use doubles in the book?

Given the symmetrical structure of Wuthering Heights, it follows naturally that Brontë should thematize doubles and doubleness. Catherine Earnshaw notes her own "double character" (66) when she tries to explain her attraction to both Edgar and Heathcliff, and their shared name suggests that Cathy Linton is, in some ways, a double for her mother. There are also many parallel pairings throughout the novel that suggests that certain characters are doubles of each other: Heathcliff and Catherine, Edgar and Isabella, Hareton and Cathy, and even Hindley and Ellen (consider the latter's deep grief when Hindley dies, and that they are 'milk siblings'). Catherine's famous insistence that "I am Heathcliff" (82) reinforces the concept that individuals can share an identity.