Anti-Catholicism
An assumption of the inherent inferiority or danger of most Catholic doctrines, institutions, and practices runs throughout the text. Celibacy in particular is singled out as not only impossible and unnatural, but as a gateway to even greater sins. Once Ambrosio has broken his vows of celibacy, he has no problem justifying rape, murder, and sorcery. The Prioress uses Agnes' sexual transgressions as an excuse to torture her psychologically and physically, locking her in a crypt with decaying bodies. In less dramatic fashion the Catholic clergy and laypeople are depicted as willing to believe anything; the nuns of St. Clare's willing accept the fantastical stories that the Prioress tells to keep them in line. This theme of anti-Catholicism stems from the historical context in which the novel was written; in Protestant England of the late eighteenth century, Catholicism was marginalized to support the burgeoning Church of England.
Pride
Though sexual desire prompts Ambrosio down the path of evil, it is pride that makes his crimes truly evil. Pride persuades Ambrosio to conceal his transgressions, even resorting to murder. The monks encouraged Ambrosio's pride in his abilities, and Ambrosio delights in his status as the most revered monk in Madrid. He enjoys receiving praise and respect, and he is determined to keep it even if it means lying and killing.
Men and Women
The novel contains numerous meditations on the nature of men and women. Women are often associated with weakness, emotion, and desirability; Antonia, for example, is desirable because of her innocence and beauty. Men, on the other hand, have a wider range of identity and action; they may be courageous and intelligent like Raymond, or deceptive and conniving like Baptiste. Yet even as the novel introduces such rigid gender differences, it also subverts them; Ambrosio exhibits a powerful masculine sex drive, but he is also described as being as timid as a woman.
Surface and Substance
You can't judge a book by its cover, as the old saying goes. In the novel, appearance is an unreliable indicator of inner character. Ambrosio is the most obvious example of this theme; on the outside, he is a virtuous monk famous for his piety, but in truth he is a murderous, lust-crazed criminal. Similarly, Matilda goes through a succession of false appearances: first she is the male novice Rosario, then she is the gentle object of Ambrosio's awakening sexual desires, and it is only towards the end of the novel that she reveals her true wicked nature, goading Ambrosio on to further crimes.
First Impressions and True Colors
Closely related to the above theme, the novel draws a distinction between the first impressions and true nature of a character. The first impression we get of a character is rarely an accurate representation of his or her actual personality. For example, when Raymond first meets Baptiste and Marguerite, he thinks that the woodsman is kind and generous whereas his wife is impolite and harsh. He quickly comes to discover that Baptiste's gracious exterior is meant to lure in victims, and Marguerite's rudeness is her reaction to her husband's life of crime. Those characters who at first seem unlikeable often prove to be the most trustworthy (such as Lorenzo), and those who seems most deserving of respect (such as Ambrosio or the Prioress) are the most despicable. This literary device also creates an atmosphere of foreboding and anxiety - the reader does not know which characters to trust.
The Supernatural
There are a number of supernatural incidents in The Monk. One of the earliest examples includes the gypsy women's prophecy that Antonia's beauty will draw the interest of a frightening predator; later, this prophecy is fulfilled when Ambrosio kidnaps and rapes her.
The long interlude describing Raymond's adventure with the Bleeding Nun, a frightening ghost, is another major example of the significance of the supernatural in the text. The story of the Bleeding Nun (a noblewoman forced into a convent who breaks her vows of chastity) foreshadows the struggles of Agnes, another wayward nun. The supernatural events in the novel are never explained or rationalized; however, supernatural events do emphasize certain traits of the characters, such as Raymond's desirability and Ambrosio's wickedness.
Sexual Desire
The fulfillment of sexual desire is one of the driving forces of the book's plot. Ambrosio is the clearest example of this - he is driven to commit heinous crimes in order to fulfill his desire for Antonia. However, nearly every character in the novel copes with the consequences of sexual desire, whether its object reciprocates it or not. Lorenzo struggles to find a way to marry Antonia. Agnes is punished by the Prioress for submitting to the sexual advances of Raymond, and Raymond becomes ill out of mourning for Agnes. The Prioress assumes that punishing the sexual indiscretions of Agnes will gain renown for her convent, though she is proven wrong. Leonella and Rodolpha introduce numerous complications into the lives of the men they become interested in. Lewis portrays sexual desire as natural and unavoidable, but a major source of conflict.
