What does Sartre mean by "existence precedes essence"? How does this doctrine figure into Roquentin's Nausea?
Sartre believed that inanimate objects were fundamentally different from human consciousness. He suggested that humans are conscious of their own existence, while objects simply exist. Human existence, or a "being-for-itself," could thus choose to be whatever it wanted. For example, a grieving widow is not sad by definition, but by choice. She chooses to create her own essence, or characteristics. An inanimate object, such as a stone, cannot choose its essence: it is a "being-in-itself." Sartre concluded that since humans must define their own essence, they must exist before they choose what their personal attributes will be. The incredible power of this choice and the overwhelming responsibility that results from it leads many people to ignore their own existence and only perceive their essence. Roquentin's Nausea is a sick feeling that something lies behind the colors, smells, weight, and appearance of objects and people. What he notices is that an object or person's essence does not exist, but is the creation of it observer. Confronted with the bare existence of objects and even himself, the comforting essence of things disappears, making him sick to his stomach.
What relation does Sartre make between time and free will? How does Roquentin's research on the Marquis de Rollebon lead him to reject the past in favor of the present?
Sartre believed that an over-reliance on the past constrained one's ability to act freely. For example, Anny wants to pretend that Roquentin has not changed in order to feel like she is still in the past. As a result, she is afraid to act in the present, unable to handle the responsibility of doing something on her own. Anny's reliance on the past to define her essence produces what Sartre called "bad faith." Roquentin similarly tries to "resuscitate" the Marquis de Rollebon to justify his existence. But he soon finds that everything he thought he knew about Rollebon was either conjecture or something he made up himself. For instance, when he looks in the mirror at the beginning of the novel, he not only sees his own face, but that of Rollebon. Roquentin concludes that the past does not exist. Listening to "Some of these Days," he understands that the second anything happens, such as a note of music, it "dies" and becomes part of the past. He thinks that one can only exist in the present. He also decides that 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 and in the present. Any attempt to order time by telling a story tries to bring the past back to life, attempting to "catch time by the tail."
What does Sartre mean by the "contingency of human existence." To what extent is contingency a major existentialist proof against rational humanism?
As Roquentin realizes throughout the novel, anything can happen at any moment. This leads him to believe that human existence is "contingent," or completely accidental. Since humans exist entirely by chance, he concludes that existence is not a necessity and that there is no reason or purpose to existence. Sartre used this argument to discredit the traditional philosophical belief that human existence was the main focal point in a reality grounded in reason. Sartre's proof paradoxically came from Charles Darwin's "rational" theory of natural selection, which argued that the evolution of humanity was an inconsequential aspect of reality. Roquentin's emphasis on contingency is a fundamental step in his awareness of the lack of purpose, or "nothingness," which makes up existence.