Paternal Love
Goriot loves his two daughters with an intensity that borders on obsession, and as a result of his love, he continuously excuses their neglectful and selfish behavior. Money contaminates almost every relationship in this novel, and the father-daughter relationship is no exception. Goriot fantasizes that providing money to his daughters will ensure a healthy relationship with his daughters. His excessive love blinds him to the reality that his daughters want only financial support from him, and are not ready to provide affection or care to him. The intensity of his paternal love is particularly striking because at this era it was not necessarily assumed that men nurtured close emotional bonds with their children, particularly with daughters. Significantly, the only other paternal relationship shown in the novel is the one between Victorine and her estranged father, who neglects his daughter in favor of his son.
Money
One of the most essential themes of the novel is money. In fact, Diana Festa-McCormick argues that "the unifying force is money" (pg. 68). Individuals, relationships, and activities are all monitored by money. Madame Vauquer judges her residents by how much money they have and how much rent they are paying. For her, the individuals are nothing more than their bank account. She falls in love with old man Goriot when she believes he is rich but once his spending decreases, she starts despising him. Vautrin convinces Eugene to consider killing Victorine’s brother by tempting him with the prospect of gaining a huge sum of money. Both of Goriot's daughters are preoccupied with money, and never seem to be able to have enough of it. Strikingly, the narrative does not punish the greedy characters, and Goriot, the one person who places love above money, dies a lonely and anguished death. In Balzac's world, a preoccupation with money seems to be essential for survival and success.
Secrets
Almost all of the boarders at the Vauquer household end up having secrets of some kind: Vautrin is a disguised criminal, Mlle. Michonneau is plotting to betray Vautrin, Rastignac is eventually involved in Vautrin's plot to get his hands on Victorine's fortune, and Goriot was once very wealthy. Even amongst seemingly unremarkable and ordinary characters, dark secrets are lurking. By paying close attention to the material details of the setting and inner lives of his characters, Balzac shows how appearances often do not align fully with reality, and there is often more to someone than there may appear to be.
Infidelity
Amongst the various aristocratic couples, infidelity is shown to be an accepted and normal reality. Delphine, Anastasie, and Madame de Beauseant all have lovers, and none of these women keep their affairs secret. In fact, other members of high society seem to know all about the various affairs that are happening amongst Parisian aristocrats. Infidelity is even normalized and tolerated to the extent that Goriot supports and encourages Delphine and Rastignac having an affair while she is still married. Marriage is shown to be largely a business arrangement that permits individuals to acquire money and social prestige, while love and desire are pursued through extramarital affairs. Nonetheless, Delphine, Anastasie, and Madame de Beauseant all end up being betrayed and deceived by their lovers.
Education
Education appears as a theme in the novel because Rastignac and Bianchon are literally students, training to work in their respective professions of law and medicine. However, Rastignac has greater ambitions than the modest life of provincial professional, and he becomes focused on acquiring a different type of education. Through advice from mentors like Vautrin and Madame de Beauseant, and from his own keen observation of how aristocrats behave around him, Rastignac starts to teach himself how to succeed at climbing the social ladder. He does not always like the lessons he learns, because he gradually becomes aware that the world is a cruel place. Still, by the end of the novel, Rastignac has learned what it takes to become the kind of man he wants to be, and he commits himself to doing whatever it takes.
Aging
Many of the boarders at the Maison Vauquer, including Goriot, are elderly, and they are often treated with mockery and a lack of respect. Goriot's daughters are also neglectful and rude towards their aging father. Traditionally, elderly characters would be shown respect, deference, and care, but in a world where the only things that matter are money, social position, and power, individuals lose power and influence as they age. Goriot is literally a relic of an older time where he once occupied a position of power and political influence, but in the new era of the restored monarchy, he seems old-fashioned and out of place.
Social Elitism
Much of the momentum of the plot results from Rastignac's determination to break into the world of the Parisian social elite. Moving in these social circles requires a complex combination of social connections, charm, cunning, and the ability to meet high standards of dress and behavior. As Rastignac learns when he unwittingly offends Anastasie, an innocent mistake can cut someone off from society permanently. Although Rastignac is ostensibly a student of law, he actually devotes his time and energy to learning how to successfully maintain the deceptions and rituals required to function as part of Parisian high society. While Rastignac's attempt to break into society are not easy, the process does show that it was possible for someone to advance their social position if they were intelligent and ambitious.