Abuse/Trauma
The protagonist, Arthur Fleck, is a victim of abuse as much as he is a villain. As a child, he was severely abused by his mother’s boyfriend, and this abuse shapes his personality as an adult and his mental condition. He can no longer trust that the society he’s a part of won’t let him down again, and he lives in a post-traumatic haze of delusion, hate, and mistrust. While he is initially presented as someone with mental health issues and inherent conditions, he later learns that they are a direct result of the trauma and abuse he suffered as a child. For Arthur, this traumatic past is damning, relegating him to a life in the margins, robbing him of any happy memories.
The film shows the ways that abuse leads to more abuse. Rather than rehabilitate and try and become a better person, Arthur becomes twisted by the abuse he suffers. He turns into a villain and takes his trauma out on others using violence. In this way, the film shows that there is something behind Arthur's mindless violence, some woundedness that has caused him to become aggressive.
Nihilism and Anarchy
When traditional social systems prove disappointing to Arthur, he becomes a nihilist, believing in nothing and simply following his chaotic impulse. When he kills the three businessmen for the first time, he has a sense of epiphany, and he feels powerful for the first time in his life. As a result of the failures of the systems that govern, people run to the streets as a show of protest, but they are not imagining a better world. Rather, they are turning to chaos and anarchy as a mode of revolution. They are fighting against a society that has neglected them and treats them like they don’t matter, by explicating the ways that "nothing matters." In the film, murder is portrayed as an act of freedom and self-realization for a troubled character like Arthur, a way to embrace nihilistic and anarchic philosophies and find some semblance of power in a disempowering system.
Mental Illness & Delusion
Arthur is a character who struggles with mental illness, which includes depressive and pessimistic feelings as well as a condition that makes it so that he laughs uncontrollably at inappropriate moments. He works with a social worker and takes several medications to help stabilize these conditions, but he does not receive qualitative or engaged care, due to his economic status. Additionally, the people in his life are not sensitive to his mental illness, and often treat him as if he's doing something wrong, rather than as a victim of a health condition. Mental illness is something that further marginalizes Arthur in society, making him feel like he will never fit in with normal people or make a difference.
As we learn later on in the film, Arthur's mother Penny also struggles with mental illness, psychosis, and delusion, which allowed her to subject him to the abuse that led to his mental illness. Both she and Arthur suffer from delusions in the film. She believes that Arthur is Thomas Wayne's son (which the film reveals is likely untrue), and Arthur believes that he has been pursuing a relationship with Sophie, when they barely know each other.
The Failure of the State
Arthur's mental illness is only exacerbated by the fact that social services are so limited in Gotham and he is unable to find adequate care. Because of his economic struggles, he must see a social worker, but halfway through the film, her office is shut down by the government in Gotham, which is driven more by profit than by the imperative of protecting and helping its ordinary citizens. In this moment, we see that the failure of the state contributes directly to Arthur's descent into madness.
Additionally, when Arthur kills the three businessmen on the subway, the act is misinterpreted as an act of class warfare, even though Arthur was not thinking in those ways. When Thomas Wayne goes on television to address the issue, he refers to lower class dissenters as "clowns," disparaging the grievances of the poor and suggesting that he does not care about their concerns. This only fires up the lower class citizens of Gotham more, who take up Arthur's violent act as a symbol for a whole movement.
When Arthur goes on Murray Franklin's show, he admits to the murders of the three businessmen. He tells Murray, "Ugh, why is everybody so upset about these guys? If it was me dying on the sidewalk you'd walk right over me! I pass you everyday and you don't notice me! But these guys? Well, because Thomas Wayne would cry about them on TV?" While he is unhinged and irrational in many ways, at times, Arthur makes cogent points about the injustice of society and the ways that elites abandon those at the bottom.
Comedy
Comedy is a major theme in the film in different ways. Firstly, Arthur is obsessed with stand-up comedy and with his television idol, Murray Franklin. Arthur dreams of overcoming his shyness, mental illness, and loneliness, by connecting with an audience through performing as a stand-up. He keeps a book of jokes that are just strange and disturbing thoughts, and goes to stand-up comedy shows where he often laughs at inappropriate moments. Additionally, Arthur has a condition that makes him laugh uncontrollably at inappropriate moments. This condition is symbolic of the ways that Arthur is out of step with mainstream culture and standards of comedy.
After he fails as a stand-up comedian and his botched performance becomes the target of mockery on The Murray Franklin Show, Arthur becomes even more alienated from society and slips even deeper into his villainous character, Joker. When he is invited to appear on Murray's show, he tells disturbing jokes, much to the chagrin of Murray and the studio audience. Arthur's distance from the mainstream comedic world runs in parallel with his general alienation, and he ruminates about the connection between society's standards and standards for what is funny and what is not. He insists, "Comedy is subjective, Murray, isn't that what they say? All of you, the system that knows so much: you decide what's right or wrong the same way you decide what's funny or not." Moments later, he frames his murder of Murray as a simple joke, saying, "What do you get when you cross a mentally ill loner with a society that abandons him and treats him like trash? You get what you fucking deserve!" In this moment, we see that Arthur's unhinged violent impulse and chaotic destructive tendencies have become aligned with his desire to make people laugh.
Transformation
The film looks at Arthur's victimization in society and the fact that he has had a difficult life, filled with abuse, mental illness, alienation, and loneliness. Because of this complete alienation, he begins to transform into a completely new person, a person who takes their pain and turns it into chaotic villainy, rather than wallowing in self-pity. Thus, he becomes Joker, a terrifying gun-toting vigilante in full clown makeup, who dances his way through life, becoming a violent showman and confident psychopath. While we see this transformation as a descent into evil, we can also see that it is a kind of confidence-boosting moment for Arthur, a coming out and a blossoming into someone who believes in themselves, even if this believing leads him to become a murderer.
Vigilantism
Another major theme in the film is vigilantism, Arthur's taking matters of justice into his own hands. While his political ideology is rather chaotic and confused, tainted by mental illness and delusion, he does have a strange sense of justice. He kills three businessmen on the subway who are harassing him and a woman on the train. Later, he kills his coworker who gave him his gun in the first place, as well as his mother, who allowed him to be abused. Arthur does not have a clear political agenda; he kills people who he believes have wronged him, because he sees himself as the ultimate victim of society's ills. In this way, he is a kind of vigilante, someone who steps in to enact vengeance and justice when the law and the state are not doing enough to protect its citizens.
