Marriage
Almost all the characters in the novel chase after marriage. Marriage is seen as part of the bedrock of society, a natural element of adult life, and an institution that protects and promotes virtue. Women regard the institution with the utmost importance so they do not find their virtue diminished. Foster provides insight into several "real" marriages though, showing how they can succeed or fail for various reasons. The equitable marriages of the Richmans and the Sumners are worthy of emulation, but marriage does not save Major Sanford from himself or his poor wife from ignominy or despair. Marriage to the wrong person can bring about a lifetime of difficulty, and for this reason the novel's protagonist mostly shuns marriage. Eliza believes that marriage lessens friendship, cuts off social engagements, and limits freedom and choice. Foster's novel attempts to show different realities in marriage, finding validity in Eliza's views as well as those who tout marriage's redeeming qualities.
Friendship
The novel treats friendship as almost as important as marriage. Eliza takes her friendships very seriously, demonstrating their importance to the formation of a young woman's character and her navigation of the often treacherous world of love and marriage. Eliza seeks advice from her friends, confesses to them a great deal of her thoughts and actions, and tries to take their counsel to heart. She lambasts marriage as the "tombstone" of friendship and evinces displeasure when marriage takes her friends away from her. However, those friends enjoy advising and critiquing Eliza a bit too much, often revealing holier-than-thou attitudes while they judge her actions and thoughts. Women could often allow their friendships to become influenced by the strict patriarchal society they navigated, caring too much for their friends' reputations and not enough for their hearts and spirits.
Virtue
Virtue was of paramount importance in the late 18th century, particularly for women. Young women were supposed to guard their virtue, shunning "rakes" and "libertines" who wanted to seduce them and instead pursuing men of sense and discretion. The focus on virtue was often very punishing, however, as women were obsessively observed, pigeonholed, judged, and censured for any apparent lapse in the protection of their virtue. Eliza experiences firsthand the intense fixation of her community on her virtue, as they label her a "coquette" and subject her to near-continuous criticism and barely-concealed hostility.
Freedom
Eliza's quest for freedom can be understood as the central theme of the novel. She views freedom as enjoying her youth and the pleasures of society, moving between social classes, and choosing the man she wants to marry. Unfortunately, such freedom was not widely available in post-revolutionary America, and Eliza's quest for it ends in shame and death. Unfettered freedom, especially for young, unmarried, and middle- or lower-class women, was considered dangerous. A patriarchal society dictated that women marry, and marry someone deemed acceptable for their station and rank. Eliza does not have the options that women in modern and contemporary America do, and is sadly punished for her attempts to subvert societal norms. Foster skillfully reveals how Eliza's fate is not entirely her own fault, but also her society's.
America
Many critics understand the novel as an exploration of America in the immediate postrevolutionary period. What kind of society did America want? What boundaries and limitations should exist in terms of freedom and equality? Foster reveals how Americans from the time had to deal with the complexities of navigating an uncertain world in which freedom and tradition/order were in flux.
Gender
Eliza inhabits a world characterized by very strict gender norms. Women should be beautiful, smart, and virtuous, but not trespass any boundaries by appearing too appealing or enjoying too much of fashionable society or the company of men. They should see their worth in their roles as wives and mothers, and not seek to delay or alter this role for themselves. Men are still judged and censured for bad behavior – Major Sanford is deemed a "rake" and encounters hostility from various sectors of his society – but have many more options available to them. Men have much more freedom to act as they wish and are not subject to constant scrutiny. It takes an extreme loss to exile them from society, as with the Major at the end of the novel. Overall, gender norms are very fixed for people in this era.
Social Class
While not a central point, the novel contains many references to social class. For example, Eliza, her family, and Mr. Boyer are from a solid middle-class background, whereas the Richmans, the Sumners, and Major Sanford, among others, are wealthier. Eliza gravitates toward the Major's wealth and the life of leisure and ease marriage to him seems to promise, but one of the central tensions in the novel is between the growing desire in the post-revolutionary period to move between social classes and the sense that doing so was, at the very least, inappropriate. Eliza is not encouraged to assume she can be with the Major, and is advised over and over again to choose Mr. Boyer. Social class is an essential component of this conflict. A healthy society is an ordered one, and any mobility between classes is suspect, even in a time period ostensibly concerned with liberty and equality (of a sort).