Although Existentialism is primarily a philosophy, existentialists emphasize artistic creation as a vital aspect of existence. As a result, Sartre often chose to combine both the finer points of his philosophy and aesthetic concerns in plays, short stories, and novels. Unlike the fiction of the famous philosopher, Voltaire, Sartre's fiction is not allegorical or mythical, but a straightforward outline of his philosophical arguments. This reliance on artistic creation to understand oneself becomes Roquentin's ultimate cure to his Nausea. Rather than give into despair, the inspirational music he hears on a jazz record both convinces him to confront the bare existence of things and write a novel.
The main theme of the novel results from Sartre's belief that "existence precedes essence." Roquentin unwittingly differentiates between inanimate objects, or a "being-in-itself," and human consciousness, or a "being-for-itself." For example, when he looks at a bartender's purple suspenders, he is distraught to find that they appear blue in some places. His feelings of Nausea come from moments like this when he realizes that he is creating the essence, or characteristics, of the objects he sees. He understands that color is just an idea, and "purple" just an inadequate word to describe something he has never seen before. He concludes that the essences of objects are just comforting "facades" that hide the unexplainable nakedness of existence. In effect, while studying the root of a chestnut tree, Roquentin realizes that the root first existed and then he attributed an essence to it by describing it as "black."
Every discovery that Roquentin makes proceeds from his epiphany that existence precedes essence. He thinks that the overwhelming a fearful presence of existence is too much for people to handle so they ignore and hide it by only perceiving its essence. He recognizes the power of a being-for-itself to chose its own essence, just as it decides what color an object is. Because of this choice, Sartre believed that humans were fundamentally free to do whatever they wanted. Indeed, Roquentin continuously states that he just wants to be free. But with this freedom comes the responsibility for one's actions. Sartre believed that this staggering responsibility makes people anxious and ultimately leads them to deny both their freedom and responsibility. For example, Anny is afraid to act because she does not want to be responsible for breaking with her past. As Sartre explained, responsibility "condemns us to be free."
The themes of time and free will also preoccupy Roquentin's search for the cause of his Nausea. His desire to be free and self-sufficient provokes him to abandon his research on the Marquis de Rollebon. He realizes that he had been attempting to "resuscitate" Rollebon in order to justify his own existence. He decides that the past is a meaningless concept that does not exist. Instead, he embraces the present as the only moment where and when things do exist. He thinks that people emphasize their past to take a "vacation from existence." For example, Anny defines herself in relation to the man Roquentin used to be. As Sartre explained, this is an example of bad faith: Anny rejects her freedom to choose her own essence because the responsibility is too great. Roquentin also thinks that people tell stories so as to put time in a recognizable and linear order, trying to "catch time by the tail." In effect, while studying Rollebon, Roquentin not only deceived himself into thinking that Rollebon was like him, but that he could fully understand himself through the intermediary of a dead man.
Roquentin's rejection of the past causes him to embrace his existence in the present. He constantly repeats "I exist" and mocks the people of Bouville who refuse to recognize their own existence. But he discovers that existence is a "deflection." He realizes that existence is "contingent," that there is no necessary reason for anything to exist. If evolution were to happen over again, the results would be completely different. Instead of reason, he finds only "nothingness," an empty vacuum that paradoxically makes up existence. Sartre uses the theme of contingency to criticize humanism's emphasis on a rational world with human existence as its focus and purpose. As Roquentin explains to the Self-Taught Man, human beings are an accidental offspring of a meaningless reality. Rather than surrender to his Nausea, Roquentin confronts his existential anguish in the face of "nothingness." Although he can't see it, "nothingness" is a force that makes up a purposeless reality, but which also inspires action. Artistic creation emerges as a means of survival, as Roquentin asserts his freedom to define his own essence by writing a novel.