Indeed, there is a contradiction in Catherine's character. Having avowed in Chapter 9 that she loves Heathcliff, their souls are alike, and she is only happy with Heathcliff--"Nelly, I am Heathcliff!"--Catherine yet declares that she will marry Edgar Linton although he and she are
as different as a moonbeam from lightning, or frost from fire.
When Nellie accuses her of wanting to marry Edgar Linton because he is young and handsome and rich, Catherine says that she plans to marry Linton because he loves her, and because of his social position, which will enable her to provide for Heathcliff, who is so badly abused by her brother Hindley. This decision of Catherine's is an impetuous one, for she admits to Nellie that even though others might love her if she met them, she has only to do with the present. Further, she tells Nellie,
"Whatever our [hers and Heathcliff's] souls are made of, his and mine are the same; and Linton's is as different as a moonbeam from lightning, or frost from fire."
Whereas Catherine has responded to Heathcliff with her heart and nature always, her reactions to Linton are as she words them, "rational[ly.]" For, Catherine feels that Heathcliff will always be to her "what he has been all his lifetime"; however, she is completely unrealistic in thinking that she can live such a dual life, married to one man, but still deeply in love with another.