The novel is written using a series of flashbacks that show up parts of Esther's past. The flashbacks primarily deal with Esther's relationship with Buddy Willard. The reader also learns more about her early college years.
The Bell Jar addresses the question of socially acceptable identity. It examines Esther's "quest to forge her own identity, to be herself rather than what others expect her to be." Esther is expected to become a housewife, and a self-sufficient woman, without the options to achieve independence. Esther feels she is a prisoner to domestic duties and she fears the loss of her inner self. The Bell Jar sets out to highlight the problems with oppressive patriarchal society in mid-20th-century America.
Esther Greenwood, the main character in The Bell Jar, describes her life as being suffocated by a bell jar. Analysis of the phrase "bell jar" shows it represents "Esther's mental suffocation by the unavoidable settling of depression upon her psyche."  Throughout the novel, Esther talks of this bell jar suffocating her and recognizes moments of clarity when the bell jar is lifted. These moments correlate to her mental state and the effect of her depression. Scholars argue about the nature of Esther's "bell jar" and what it can stand for. Some say it is a retaliation against suburban lifestyle, others believe it represents the standards set for a woman's life. However, when considering the nature of Sylvia Plath's own life and death and the parallels between The Bell Jar and her life, it is hard to ignore the theme of mental illness.
Psychiatrist Aaron Beck studied Esther's mental illness and notes two causes of depression evident in her life. The first is formed from early traumatic experiences, her father's death when she was 9 years old. It is evident how affected she is by this loss when she wonders, "I thought how strange it had never occurred to me before that I was only purely happy until I was nine years old." The second cause of her depression is from her perfectionist ideologies. Esther is a woman of many achievements—college, internships, and perfect grades. It is this success that puts the unattainable goals into her head and when she doesn't achieve them her mental health suffers. Esther laments, "The trouble was, I had been inadequate all along, I simply hadn't thought about it."
Esther Greenwood has an obvious mental break- that being her suicide attempt which dictates the latter half of the novel. However, Esther's entire life shows warning signs that cause this depressive downfall. The novel begins with her negative thoughts surrounding all her past and current life decisions. It is this mindset mixed with the childhood trauma and perfectionist attitude that causes her descent that leads her to attempt suicide.
This novel gives an account of the treatment of mental health in the 1950s. Plath speaks through Esther's narrative to describe her experience of her mental health treatment. Just as this novel gives way to feminist discourse and challenges the way of life for women in the 1950s, it also gives a case study of a woman struggling with mental health.