Themes are the fundamental and often universal ideas explored in a literary work.

Subjective Experience versus Objective Knowledge

The competition between these two forces—subjective experience and objective knowledge—characterize the conflict experienced by the two main characters of The Moonstone, Rachel Verinder and Franklin Blake. If we take the dichotomy between subjectivity and objectivity to mean something like feeling versus fact, we can begin to see Rachel Verinder's dilemma as the conflict between the evidence of her senses that Franklin Blake stole her diamond and her overwhelming love for Franklin. Franklin's dilemma is similar—he must reconcile the objective evidence that he stole Rachel's diamond with his subjective impression that he would not have done any such thing. These two dilemmas are paradoxically gestured to the concern, stemming supposedly from his European education, that Franklin has with the "Subjective- Objective" and "Objective-Subjective" viewpoints throughout the novel.

If we take the subjective/objective dichotomy to refer also to the interaction between character (subjective) and circumstance (objective), Collins himself explicitly stated his interest in this interaction in the original preface to The Moonstone. Here Collins proclaims his "attempt made, here, to trace the influence of character on circumstances. The conduct pursued, under a sudden emergency, by a young girl, supplies the foundation on which I have built this book." Thus we see that objectivity and subjectivity do not have to be in competition—the novel is also interested in the effect of each upon the other, as when Rachel's subjectivity—specifically her characteristic unwillingness to tell on another—enables the plot of The Moonstone by continuing to hide the thief's identity. The effect of subjectivity on objective fact is also traced in each of The Moonstone's narratives. Each character reports events and facts surrounding the disappearance of the diamond, yet more often than not, the report of these facts is affected by his or her personal perceptions and opinions.

The Nobility of Self-Sacrifice

The theme of self-sacrifice first arises in relation to the Indians in pursuit of the diamond. The Indians, guardians of the diamond, were born high-caste Brahmins in India. In order to track the diamond under-cover, they have disguised themselves as low-caste Indians and have thus violated their caste and, by extension, sacrificed their place in the next world. It is Murthwaite who points this out to the English, and it becomes a reason to respect the Indians and the urgency of their quest to pursue the diamond. The novel ends with the ceremony that features not only the replacement of the diamond in India, but the dramatization of the sacrifices made by the three Indians and the further cleansing and penance they must continue to undergo. The willingness of members of the Hindu society to sacrifice themselves for the spiritual good of the whole is presented as a source of strength for India.

The English counterpart to this noble self-sacrifice is Rachel Verinder, who sacrifices her public reputation by keeping the secret of Franklin's guilt from everyone. While the Indians have made their sacrifice in the name of spirituality, Rachel's sacrifice is made in the name of love. It is this conventional love of Rachel for Franklin (the basis of the marriage plot of the novel) that is presented as English society's competing source of strength.

The Disparity Between Different Systems of Value

When the diamond is given to Rachel Verinder by Franklin and she shows it to the company assembled in Chapter IX of the First Period, everyone is entranced by its strange beauty bbut Godfrey Ablewhite, who says to Betteredge, "Carbon, Betteredge! mere carbon, my good friend, after all!" Not coincidentally, it is Godfrey who sees the diamond, and later uses it, for its cash-value as a commodity, while others view the diamond for its non-market value.

The Moonstone's entrance into various systems of value traces its trajectory through the novel. When the diamond is part of the Indian Moon god idol, it is spiritually valuable. When stolen by John Herncastle and willed to his niece, the diamond becomes valuable as an exotic heirloom—in other words, it is so valuable that it is "priceless." It takes Godfrey Ablewhite and Septimus Luker to place the diamond into the market economy and put cash value on it.

These different spheres of value—spiritual, familial, and commercial—are also used to define the various communities of the novel—the East; upper-class, provincial English; and modern, urban English, respectively.

The Unwelcome Return of the Past

The preface to The Moonstone alerts us to the fact that the diamond carries with it a menacing history that can arise and infect the present with bad luck. Thus contemporary English society must pay for crimes committed (by extension) by imperial England. This threatened return of an evil, or shameful past (in this case, John Herncastle's violent conduct), is a theme that defines many of the characters of the novel, as well as the diamond itself. Ezra Jennings, in Chapter IX of the Third Narrative in the Second Period, says, "Perhaps we should all be happier, if we could but completely forget!" He is speaking explicitly of Mr. Candy, but he is also referring to his own shameful past, which arises again and again in the present via painful gossip. Rosanna Spearman, too, finds she cannot escape her painful past, when she is immediately suspected of having stolen the Moonstone because of her history of being a thief.

The Moonstone seems to advocate a straightforward interaction with one's past as the surest way of escaping the haunting of that past. Thus, once Franklin Blake lives through his past again in the recreation of the night of the diamond theft, he becomes completely free from the shameful implications of that past.