The novel's tone is didactic, discontented, and often ironic. In many ways, Foster uses Eliza's tragic downfall to express a clear moral lesson: To avoid Eliza's fate, young women should avoid libertines like Sanford and cultivate respectable relationships with virtuous men like Boyer. In keeping with this argument, women like Lucy and Mrs. Richman, whom Eliza initially dismisses as prudish, turn out to be absolutely right about the results of her affair with Sanford. Such women often give Eliza explicit advice on her behavior—for example, Lucy warns her that her reputation is a "jewel" she must guard assiduously—and their warnings suggest that the novel's purpose is to instruct young female readers.
At the same time, by making Eliza an extremely sympathetic character, and showing how her female friends and family stick by her no matter what she does, Foster cultivates a tone of discontent with the harsh fates of rebellious women in this highly sexist society. While warnings from Lucy and Mrs. Richman sometimes carry a judgmental tone, by the time Eliza actually delivers her child and dies, they have adopted an uncritical and mournful tone in discussing her: Julia describes Mrs. Wharton as pitying Eliza's lonely death rather than repudiating her for her behavior, and the headstone they ultimately design describes Eliza as displaying "uncommon tenderness and affection" to her friends. Meanwhile, Julia and Lucy are united in their belief that Sanford is to blame for Eliza's ruin and ought to be "banished from human society." This change in tone undermines the novel's initial moral certainty and suggests that Eliza's downfall is a result of the social pressures placed on women, rather than her own folly.
In many moments, Foster uses an ironic tone to bridge the gap between her explicitly instructive approach and underlying criticism of sexist norms. For example, in Boyer's final letter to Eliza, he chastises her for extravagance in her behavior and dress, writing that,
Too large a portion of your time is devoted to the adorning of your person.
Eliza sees this letter as a just rebuke from a virtuous man. But the reader knows from Boyer's correspondence with his own friends that he was initially attracted to Eliza because of her carefully cultivated appearance and charm; he only objects to Eliza's alleged vanity when it becomes clear that he won't be able to possess her beauty through marriage. Moments like this, which showcase Boyer's hypocrisy while appearing to affirm his beliefs, allow the novel to be both didactic and discontented at the same time.
