Love
In the popular imagination, the relationship of Heathcliff and Cathy is seen as one of the greatest love stories in English literature. It is important to consider why. They never consummate their love, and so could the intensity of their feeling owe as much to frustration as deep feeling? If so, does this matter and is it proof of a deeper bond than those of marriage and sex? It is often overlooked that Heathcliff and Cathy are brought up as siblings. Thus their relationship contravenes nearly all the social and moral boundaries imposed by familial roles. In The English Novel, Form and Function (1953), Dorothy Van Ghent drew attention to the significance of doors and windows throughout the novel, suggesting that they are representative of these boundaries. The symbolism is used to particular effect when Cathy is confined to her room in Volume 1, Chapter 12 (the importance of this motif is explored in greater detail under the theme of 'Nature').
Romantic allusions attached to the idea of 'union' with another are pushed to the extreme. Heathcliff and Cathy attempt to conquer the separation enforced by death, but in doing so transgress many taboos. Any sentimentalism invoked by Heathcliff's plans to be buried with Cathy is eroded by his morbid attempts to dig up her corpse for one last embrace. Similarly, Cathy's rejection of heaven and the implications of her ghost, as well as the legend of the lovers' ghosts wandering the moors, stress how the conventional barriers set up between dreams and reality, life and death, are always under threat.
The violence that colours relationships in the novel also characterizes Heathcliff and Cathy's expression of love. Bronte depicts the positive and negative attributes of violent natures, and is not afraid to depict raw emotion. However, paradoxically, the cruelty Heathcliff shows towards others does not diminish our belief in his capacity for love, nor the profundity of their relationship. In fact, it makes him more realistically human and therefore more attractive and sympathetic than the conventional romantic hero (see the charismatic Darcy in Pride and Prejudice).
However, considering the fact that Heathcliff loses all momentum for revenge towards the end of the book (and as he comes nearer to union with Cathy in death), it could be argued that Bronte is showing us that it is necessary for violence - whether channelled through hate or love - to be tempered if you are to achieve lasting happiness in the world. Forgiveness is first brought into the novel through Lockwood's dream at the beginning. The inability of characters to forgive others is shown to be the cause of deep unhappiness. Thus, Heathcliff's inability to forgive Cathy for marrying Edgar indirectly leads to her death; his failure to forgive Hindley for abusing him ricochets misery through subsequent generations. The marriage of Hareton and Catherine, then, can be seen as the resolution of the earlier tempestuous love of Heathcliff and Cathy, the younger lovers being tempered refined versions of the first.
Faith
Conventional religious faith is represented by Joseph, who imposes constraint on the inhabitants of Wuthering Heights, particularly Heathcliff and Cathy. The fact that he is unsympathetic and cruel has been taken as indication of Bronte's views concerning Christian teachings. Heathcliff's rebellion is marked by allusions to the devil, and the scene depicting him and Cathy looking in on Thrushcross Grange has been interpreted as the devil looking in on Adam and Eve in the Garden of Eden.
In line with Bronte's implied criticism of organized religion is the constancy of Heathcliff's love for Cathy. His marriage to Isabella and his efforts towards revenge do not lessen its impact; rather, they emphasize his fallibility and humanity, and this in turn serves only to elevate his love and faithfulness to Cathy's memory. Bronte depicts superior, transcendent emotions in flawed characters. Arguably she is presenting a freer alternative faith more focused on the individual. This idea is particularly intriguing in light of the prominence of nature in the novel.
Nature
We are presented with the dichotomy of nature and culture, primitivism and civilization. Wuthering Heights is symbolic of nature, unrefined and raw; Thrushcross Grange is symbolic of sophistication and culture. The abundance of animal imagery in the portrayal of the Heights compounds our sense of its baseness. This also underlines the parallel between Heathcliff and the devil, with implications for the depiction of religion in the novel as a whole.
The inhabitants resemble their homes, and contact with 'opposite' natures results in antagonism and conflict. Only like natures are deemed to be compatible, in that the union satisfies spiritually and emotionally. The love of Cathy and Heathcliff is superior to Cathy and Edgar's, then, because Cathy and Heathcliff's natures are the same. Cathy expresses this in Volume 1, Chapter 9, and Dorothy Van Ghent elaborates upon this in her work on the notion of 'otherness' in The English Novel, Form and Function. She argues that the windows and doors are used by Bronte to separate and connect polar opposites. However, the boundaries are perpetually transgressed, so the presence of any barrier immediately establishes tension. Control over others is exercised in locking others in or out, but such attempts are always undermined.
At the beginning of Wuthering Heights, Lockwood declares himself to be cultured and refined and is held up as the archetypal Victorian gentleman. It has been suggested, then, that Bronte is criticizing Victorian values. His attitude towards love and infantile reaction in the face of reciprocation is paltry in comparison with Heathcliff's unashamed displays of emotion. Nature is also used to account for the innate violence of the inhabitants at the Heights. Believing that it is an intrinsic part of Heathcliff and Cathy accommodates the display of love and hate shown by them both, undermining in turn the idea that these emotions are paradoxical. However, the imagery surrounding the courtship of Catherine and Hareton suggests that Bronte is showing how such violence must be moderated in order for lasting happiness to be achieved. A compromise between the unrefined Wuthering Heights and the refined Thrushcross Grange must be sought.