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

The Claim of the Past Upon Present Identity

Both characters and places in The Mill on the Floss are presented as the current products of multi-generational gestation. The very architecture of St. Ogg's bears its hundreds of years of history within it. Similarly, Maggie and Tom are the hereditary products of two competing family lines—the Tullivers and the Dodsons—that have long histories and tendencies. In the novel, the past holds a cumulative presence and has a determining effect upon characters who are open to its influence. The first, carefully sketched out book about Maggie and Tom's childhood becomes the past of the rest of the novel. Maggie holds the memory of her childhood sacred and her connection to that time comes to affects her future behavior. Here, the past is not something to be escaped nor is it something that will rise again to threaten, but it is instead an inherent part of Maggie's (and her father's) character, making fidelity to it a necessity. Book First clearly demonstrates the painfulness of life without a past—the depths of Maggie's childhood emotions are nearly unbearable to her because she has no past of conquered troubles to look back upon with which to put her present situation in perspective. Stephen is held up as an example of the dangers of neglecting the past. Dr. Kenn, a sort of moral yardstick within the novel, complains of this neglect of the past of which Stephen is a part and Maggie has worked against: "At present everything seems tending toward the relaxation of ties—toward the substitution of wayward choice for the adherence to obligation which has its roots in the past." Thus, without a recognition of the past with which to form one's character, one is left only to the whims of the moment and subject to emotional extremes and eventual loneliness.

The Importance of Sympathy

The Mill on the Floss is not a religious novel, but it is highly concerned with a morality that should function among all people and should aspire to a compassionate connection with others through sympathy. The parable of St. Ogg rewards the ferryman's unquestioning sympathy with another, and Maggie, in her final recreation of the St. Ogg scene during the flood, is vindicated on the grounds of her deep sympathy with others. The opposite of this sympathy within the novel finds the form of variations of egoism. Tom has not the capability of sympathizing with Maggie. He is aligned with the narrow, self-serving ethic of the rising entrepreneur: Tom explains to Mr. Deane that he cares about his own standing, and Mr. Deane compliments him, "That's the right spirit, and I never refuse to help anybody if they've a mind to do themselves justice." Stephen, too, is seen as a figure that puts himself before others. His arguments in favor of his and Maggie's elopement all revolve around the privileging of his own emotion over that of others', even Maggie's. In contrast, Maggie's, Philip's, and Lucy's mutual sympathy is upheld as the moral triumph within the tragedy of the last book. Eliot herself believed that the purpose of art is to present the reader with realistic circumstances and characters that will ultimately enlarge the reader's capacity for sympathy with others. We can see this logic working against Maggie's young asceticism. Maggie's self-denial becomes morally injurious to her because she is denying herself the very intellectual and artistic experiences that would help her understand her own plight and have pity for the plight of others.

Practical Knowledge Versus Bookish Knowledge

The Mill on the Floss, especially in the first half of the novel, is quite concerned about education and types of knowledge. Much of the early chapters are devoted to laying out the differences between Tom's and Maggie's modes of knowledge. Tom's knowledge is practical: "He knew all about worms, and fish, and those things; and what birds were mischievous, and how padlocks opened, and which way the handles of the gates were to be lifted." This knowledge is tangible and natural—it brings Tom in closer association to the world around him. Meanwhile, Maggie's knowledge is slightly more complicated. Other characters refer to it as "uncanny," and her imagination and love of books are often depicted as a way for her to escape the world around her or to rise above it—"The world outside the books was not a happy one, Maggie felt." Part of the tragedy of Maggie and Tom Tulliver is that Tom received the education that Maggie should have had. Instead of Maggie blossoming, Tom is trapped. When Tom must make a living in the world, he discovers that his bookish education will win him nothing: Mr. Deane tells Tom, "The world isn't made of pen, ink, and paper, and if you're to get on in the world, young man, you must know what the world's made of." Tom soon returns and takes advantage of his skills for practical knowledge, making good in the newly entrepreneurial world. Tom's practical knowledge is always depicted as a source of superiority for Tom. From his childhood on, Tom has no patience for Maggie's intellectual curiosity. The narrowness of Tom's miseducation under Mr. Stelling seems somewhat related to the narrowness of Tom's tolerance for others' modes of knowledge. Yet Eliot remains clear that Maggie's intellectualism makes her Tom's superior in this case—"the responsibility of tolerance lies with those who have the wider vision."

The Effect of Society Upon the Individual

Society is never revealed to be a completely determining factor in the destiny of Eliot's main characters—for example, Maggie's tragedy originates in her internal competing impulses, not in her public disgrace. Yet, Eliot remains concerned with the workings of a community—both social and economic—and tracks their interrelations, as well as their effect upon character, as part of her realism. The Mill on the Floss sets up a geography of towns and land holdings—St. Ogg's, Basset, Garum Firs, Dorlcote Mill—and describes the tone of each community (such as the run- down population of Basset). The novel tracks the growth of the particular society of St. Ogg's, referencing the new force of economic trends like entrepreneurial capitalism or innovations like the steam engine. A wide cast of characters aims to outline different strata in the society—such as the Dodsons, or the Miss Guests—through their common values, economic standing, and social circles. In the first part of the novel, Eliot alludes to the effect these communal forces have on Maggie's and Tom's formation. Toward the end of the novel, the detailed background of St. Ogg's society functions as a contrast against which Maggie seems freshly simple and genuine.