Roquentin finds himself unable to complete his research on the Marquis de Rollebon. He used to enjoy Rollebon's overt lies in letters to contemporary aristocrats, but Roquentin now feels that Rollebon is lying to him personally. He had hoped that by researching Rollebon, he would discover the truth about him just as easily as he could learn about someone who was still alive. Yet, not only is Rollebon dead but Roquentin thinks any understanding of the past to be a futile pursuit at best. The Rollebon he though he knew was nothing but a man of his own creation, who ended up disgusting him as much as he disgusts himself.
Roquentin's attention turns to women instead. He tries to fondle Francoiseunder a cafe table, but is thoroughly disgusted by the idea of sex. He imagines ants and other vermin crawling up her leg, while a sudden attack of the Nausea makes him want to vomit. He then receives a letter from his old lover, Anny. They have not seen or spoken to each other since they parted ways in Vietnam five years earlier. She writes that she is in Paris and desperately needs to see him. Roquentin is first excited to see her but then recalls all the trouble they had communicating with each other. He realizes that it is completely his decision what happens next: he can either go see her or do nothing. He says that he staggers under the weight of his responsibility.
When he tries to remember more about Anny, he realizes that he can never have any real memory of her: he feels that it is impossible to think of someone in the past. Roquentin concludes that the past does not exist; in its place there is only an enormous vacuum. He then comprehends that if one cannot learn from the past they cannot learn from the present. Historians try to describe current events and people in terms of a convenient but meaningless past: Lenin was a Russian Robespierre, while Robespierre was a French Cromwell. In the end, one is left with relative comparisons that signify nothing. Roquentin wants to free himself from the meaningless past by perceiving objects and people on their own terms.
Roquentin soon realizes that one of things that has been bothering him is the meaning of existence. While roaming through the halls of the Bouville portrait museum, he is confronted with hundreds of painted eyes both looking at him and recalling the experiences that made them worthy portrait subjects. Roquentin thinks that these men were so afraid of death that they relied on their past experiences to give meaning to their lives. But Roquentin decides that the past is useless since death can come at any moment--why try and hide from it?
The Roquentin/Rollebon duality is fully explained in this section. As Roquentin abandons his historical research he realizes that Rollebon had represented the only "justification" for his existence. Sartre thus evokes three major existentialist themes through this relationship. First, Roquentin must confront the meaningless of the past. Everything that he thought he understood about the marquis was either a lie or something that Roquentin inadvertently made up himself. As he exclaims in frustration, his research explains "nothing, nothing at all; nothing." Second, since he had been imagining what Rollebon was like rather than actually knowing the truth about him, Roquentin created a figure in his own image, giving the marquis many of his own personal characteristics. Nevertheless, even in the guise of a "convenient past," Rollebon still makes no sense to him. As a result, Roquentin must confront the truth that he no longer makes any sense to himself. Behind Rollebon's seemingly persuasive "justification" for his existence, Roquentin finds the real meaning of existence: nothing. Finally, Rollebon's lies recall Sartre's doctrine of self-deception. Roquentin discovers that he has been lying to himself. He had been trying to hide the meaningless of his own existence through the intermediary of Rollebon. Behind Rollebon's lies and Roquentin's own lies about Rollebon to himself, he finds only self-loathing and nothingness.
Roquentin's relationships with women also reveal a number of Sartre's ideas about existence. For example, he often evokes and describes dirty body parts and especially dirty genitalia to confront Roquentin with the overwhelming and disgusting nature of existence. Sartre often spoke of the detestability of existence. His descriptions of dirt and vermin "hide" the essences, or characteristics of objects, making the usually invisible idea of their existence a startling reality. When Roquentin touches a dirty object he is disgusted by the sensation of the object's "existence," rather than the physical characteristics that make up its essence.