The predominant theme of The Phantom of the Opera is the divide between appearance and reality. The theatrical setting itself emphasizes this theme, since theater is all about creating an illusion to enrapture an audience. As mentioned in the other answer, there is the contrast between the splendor of the...
The predominant theme of The Phantom of the Opera is the divide between appearance and reality. The theatrical setting itself emphasizes this theme, since theater is all about creating an illusion to enrapture an audience. As mentioned in the other answer, there is the contrast between the splendor of the Paris Opera House itself and the sewers beneath it where Erik dwells. The masquerade where Christine tells Raoul of her kidnapping is also an extension of this idea. After all, what is a masquerade but a party where people wear masks and pretend to be something they are not?
The character of Erik also embodies this theme of illusion and reality. He essentially has three identities, only one of which is genuine: Erik the man, the Opera Ghost, and the Angel of Music. The latter two identities are "masks" Erik uses in his interactions with others, intimidating the opera house management as the seemingly omnipresent Ghost and forming a mentor-student bond with Christine by pretending to be a divine spirit sent by her dead father.
Another theme is the shallowness of society and the way it forces limitations upon individuals. Though Erik's penchant for violence and vengeance make him villainous, he is also pitiable, because he was driven to his pathetic state by social rejection. Erik's intelligence and artistic genius were ignored because of his ugly face. The narrator observes that "with an ordinary face, he would have been one of the noblest members of the human race. He had a heart great enough to hold the empire of the world, and in the end he had to be content with a cellar." Society's shallowness is also illustrated with the romantic relationship between Christine and Raoul. Raoul's brother Phillippe is okay with Christine being Raoul's mistress, but he opposes their marriage because of their unequal social rank.
The novel's main motif is music as a form of expression. In his opera Don Juan Triumphant, Erik communicates his own romantic frustration and longing. Don Juan the great lover, brilliant but damned, becomes an avatar for Erik himself. The opera Faust which figures prominently can be seen as a parallel to Christine's situation. In the Faust story, the protagonist makes a deal with the devil in exchange for pleasure and wealth; in Phantom, Christine comes close to losing her freedom and happiness when she allows Erik to control her life in exchange for his aid in pursuing her artistic ambitions.