Societal Pressure
A great deal of the novel concerns the expectations that others have for Esther with regards to behavior and her future, as well as the expectations that Esther has for other. This is most explicit in the societal expectations that Esther feels concerning decisions about a possible career and family. Esther feels that she is pressured to succeed in whatever career she chooses, despite the fact that she cannot yet even decide on which career path she will pursue. In addition, Esther also feels pressured concerning proper codes of behavior, particularly with regard to sexuality. She is constantly monitored by others, including her mother, who gives her a pamphlet on female sexuality, and even her neighbors, such as Mrs. Ockenden, who spies on her and reports back any indiscretions. Yet Esther does in some sense accept this pressure on her and even judges others' behavior by similar standards, as when she begins to loathe Buddy Willard for failing to live up to her expectations of him by having an affair with a waitress. This can also be seen in Esther's attitude toward the sophisticated and mature Doreen, who intimidates Esther by not conforming to the same expectations that Esther follows. The theme of societal pressure even continues into the mental hospital, where the greatest concern of Esther's mother and even some of the patients is that they will not be accepted in their particular social circles because of their mental illness.
Female Sexuality
Many of Esther's problems stem from a conflicted view of female sexuality. Esther is preoccupied with her virginity throughout the novel, separating the world two distinct categories: those who have and who have not had sex. She views sexually permissive women such as Doreen as objects of fascination and often scorn, but nevertheless believes that they hold some secret to life that Esther lacks. Plath relates female sexuality to a sense of empowerment in the novel and finds it to be a key facet of Esther's recovery to greater mental health. It is only when Esther takes control of her own sexuality by being "fitted" (presumably for a diaphragm) that she gains the sense of freedom that has eluded her throughout the novel. Plath contrasts the independent form of sexuality shown by Esther with more conventional and dependent modes; she celebrates Esther's decision to find a man herself over the choice to submit herself to the demands of Buddy Willard merely to gain sexual gratification.
Confinement
A sense of confinement permeates Plath's novel, even as represented by the bell jar that forms the title of the book. The bell jar symbolizes Esther's suffocation, for the jar intends to preserve its ornamental contents but instead traps them in stale air. Plath includes several instances in which Esther imagines herself as confined, including when she compares herself to a character in a short story and imagines herself trapped up in a tree unable to decide which fig (each representing a different career path) to choose. Even the place where Esther is found after her suicide attempt represents this sense of confinement; Esther is found essentially holed up in her basement. However, this is the only instance in the novel that finds Esther literally trapped; the other instances in which this theme appears are allegorical, demonstrating that Esther's sense of confinement is largely mental. The sense that she is trapped is the most obvious manifestation of her mental illness.
Motherhood
The mother-daughter relationship is the central one of the novel and the one in which Plath frames every relationship that deviates from this model. Although the actual interaction between Esther and her mother receives little attention in comparison to other relationships, Plath frames every other relationship between two women in terms of the maternal bond. Esther wishes that Jay Cee were her mother instead of the one she actually has, and even compares DR. Nolan to her mother, finding her a cross between her mother and Myrna Loy. This is a relatively idealized sense of motherhood in comparison to the other occurrences of this theme that Plath includes. The theme of becoming a mother is treated as foreign and grotesque, as shown by Esther's visit to the hospital where she watches a baby's birth and sees miscarriages in bottles, and by the character of Dodo Conway, a mother of six who fascinates and horrifies Esther for having so many children.
Sexuality and Violence
During several instances, Sylvia Plath relates sexuality to violence against women, finding the two concepts significantly linked. This occurs when Esther finds herself in the apartment as Lenny Shepherd and Doreen prepare to have sex through violent foreplay that even suggests rape. This becomes more explicit and unambiguous during the actual rape attempt against Esther by Marco, who uses sexual violence as a means of asserting his power over Esther and, in general, all women. This theme finds a final expression when Esther loses her virginity to Irwin and suffers intense bleeding. This occurrence is the most morally ambiguous, for the event is seemingly one that would empower Esther but instead finds her in some sense a victim.
