‘[In Wuthering Heights,] we are shown two opposed principles, symbolised in the novel in the two houses and their occupants, Wuthering Heights on its bleak eminence, ‘wuthering’ being a significant provincial adjective descriptive of the atmospheric tumult to which its station is exposed in stormy weather’, and Thrushcross Grange in the fat valley below. They stand respectively, though any label is inadequate and is ‘shorthand’ only, for the principle of energy and storm one the one hand is the principle of calm, of settled assurance, on the other.
And they are not only principles; they were as it were elements: the children of one cannot breathe in another.’
(Taken from ‘The English Novel (A Short Critical History)’ by Walter Allen 1954)
I believe that the statement “The children of one cannot breathe in another” explains the situation that Catherine is put in when she moves from one house to the other. Catherine moves from freedom to restrictions in less than a few days; her character symbolises freedom and general adrenalising behaviour. For example she runs barefoot across the moors with Heathcliff, she resembles nature in its pure form. In Wuthering Heights, Catherine is free to be who she is because the house atmosphere lets her, but when she moves to Thrushcross Grange in her later years she is unwillingly changed because the house she is now in does not allow her to be who she is. It makes her into a more reserved, quiet person, which is not her at all. As a result of this she becomes ill due to her lack of freedom.
In her fever, Catherine reveals that her true emotional identity has not altered since she was twelve, just before she stayed with the Lintons for some weeks. Everything that happened to her since then ceases to have any importance when she is ill:
“…Supposing at twelve years old, I had been wrenched from the Heights, and every early association, and my all in all, as Heathcliff was at that time, and been converted, at a stroke, into Mrs. Linton, the lady of Thrushcross Grange, and the wife of a stranger; an exile, and outcast, thenceforth, from what had been my world You may fancy a glimpse at the abyss where I grovelled!”
Catherine’s true nature has been closed away; she has been cooped up in the world of Thrushcross Grange and Edgar. She is stuck behind a window looking at the foggy moors; this symbolises the gaol it seems that she is in and not just the weather that so happens to be there anyway. Had she been in Wuthering Heights she would have been out on the moors running around and generally having an adrenalising time. The only time that Catherine is happy is when Heathcliff comes in Thrushcross Grange to see her. This freedom is a requirement that has been lacking in her life in Thrushcross Grange, she cannot breathe, she is denied of air, supposedly; and this is what kills her.
This difference between the two houses seems to overwhelm Catherine when she moves from Wuthering Heights to Thrushcross Grange because she cannot do any more what she could do with Heathcliff. She cannot run around, she cannot be active; she has to be someone she is not; a quiet young woman who is getting ready for marriage. That pressure for becoming a young woman has an overpowering effect that does not help Catherine at all. Because of this change, Catherine is forced to be without her individuality, which eventually claims her life. The only person who can save her from this whilst in Thrushcross Grange is Heathcliff as he is part of her and vice versa.
In chapter fifteen there is a passionate scene between Catherine and Heathcliff and is probably the emotional climax of the novel, though it only marks the middle of the book. It reveals how little their love relies on pleasure: they can hardly be said to be fond of one another, or to enjoy each other’s company, yet they are absolutely necessary to each other. It is as though they were members of a different species from other humans, who belonged together.
Ellen says: “The two, to a cool spectator, made a strange and fearsome picture.” Catherine tore Heathcliff’s hair, and he left bruises on her arm. Later, he “foamed like a mad dog, and gathered her to him with greedy jealousy. [Ellen] did not feel as though [she] were in the company of a member of [her] own species.” Love appears to be a form of madness. The strange thing is that Catherine does not find Heathcliff attractive she simply finds him unavoidable, a part of herself. Their emotional reunion is counteracted by Ellen’s cool and rather unsympathetic narration: their passionate conversation is partly destroyed with dry commentary on her part.
The principals of each house are worlds apart even though they are in very close proximity:
Wuthering Heights is energetic and free, but also suspicious and cunning.
Thrushcross Grange is calm and reserved but also destroying and smart.
When Catherine Junior is born and bred she shows values of both houses that the occupants of both of the houses could not demonstrate at all. She is the one who harmonizes the two houses and resolves it all. Catherine Senior had to die for the whole predicament to be utterly settled. This is the only way in which the novel accomplishes complete harmony. Catherine Junior is happy to live in either house as she has been brought up so that this is possible; she is not nearly as extreme as her mother or Edgar enabling her so to do.