From Husserl to Heidegger
Sartre was influenced at the time by the philosophy of Edmund Husserl and his phenomenological method. He received a stipend from the Institut Français, allowing him to study in Berlin with Husserl and Martin Heidegger in 1932, as he began writing the novel.
Roy Elveton reports:
In January, 1939, one year after the death of Edmund Husserl, Sartre published a short essay entitled 'Husserl's Central Idea.' In the space of a few paragraphs, Sartre rejects the epistemology of Descartes and the neo-Kantians and their view of consciousness's relationship to the world. Consciousness is not related to the world by virtue of a set of mental representations and acts of mental synthesis that combine such representations to provide us with our knowledge of the external world. Husserl's intentional theory of consciousness provides the only acceptable alternative: 'Consciousness and the world are immediately given together: the world, essentially external to consciousness, is essentially related to it.' The only appropriate image for intentionality and our knowing relationship to the world is that of an 'explosion': 'to know is to "explode" toward' an object in the world, an object 'beyond oneself, over there...towards that which is not oneself...out of oneself.'
Following Husserl, Sartre views absurdity as a quality of all existing objects (and of the material world collectively), independent of any stance humans might take with respect to them. Our consciousness of an object does not inhere in the object itself. Thus in the early portions of the novel, Roquentin, who takes no attitude towards objects and has no stake in them, is totally estranged from the world he experiences. The objects themselves, in their brute existence, have only participation in a meaningless flow of events: they are superfluous. This alienation from objects casts doubt for him, in turn, on his own validity and even his own existence.
Roquentin says of physical objects that, for them, "to exist is simply to be there." When he has the revelation at the chestnut tree, this "fundamental absurdity" of the world does not go away. What changes then is his attitude. By recognizing that objects won't supply meaning in themselves, but people must supply it for them – that Roquentin himself must create meaning in his own life – he becomes both responsible and free. The absurdity becomes, for him, "the key to existence."
Victoria Best writes:
Language proves to be a fragile barrier between Roquentin and the external world, failing to refer to objects and thus place them in a scheme of meaning. Once language collapses it becomes evident that words also give a measure of control and superiority to the speaker by keeping the world at bay; when they fail in this function, Roquentin is instantly vulnerable, unprotected.
Thus, although, in some senses, Sartre's philosophy in Nausea derives from Husserl and ultimately from René Descartes, the strong role he gives to the contingent randomness of physical objects contrasts with their commitment to the role of necessity. (Elveton mentions that, unknown to Sartre, Husserl himself was developing the same ideas, but in manuscripts that remained unpublished.)
Ethan Kleinberg writes that, more than Husserl, it was Martin Heidegger who appealed to Sartre's sense of radical individualism. He says, "for Sartre, the question of being was always and only a question of personal being. The dilemma of the individual confronting the overwhelming problem of understanding the relationship of consciousness to things, of being to things, is the central focus" of Nausea. Eventually, "in his reworking of Husserl, Sartre found himself coming back to the themes he had absorbed from Heidegger's Was ist Metaphysik?" Nausea was a prelude to Sartre's sustained attempt to follow Heidegger's Sein und Zeit by analyzing human experience as various ontological modes, or ways of being in the world.
In 1937, just as Sartre was finishing Nausea and getting it to press, he wrote an essay, The Transcendence of the Ego. He still agreed with Husserl that consciousness is "about" objects or, as they say, it "intends" them – rather than forming within itself a duplicate, an inner representation of an outward object. The material objects of consciousness (or "objects of intention") exist in their own right, independent and without any residue accumulating in them from our awareness of them. However, the new idea in this essay was that Sartre now differed in also believing that the person's ego itself is also "in the world," an object of consciousness to be discovered, rather than the totally known subject of consciousness. In the novel, not only Roquentin's consciousness but his own body also becomes objectified in his new, alarming perception.
And so Sartre parted company with Husserl over the latter's belief in a transcendent ego, which Sartre believed instead was neither formally nor materially in consciousness, but outside it: in the world.
This seemingly technical change fit with Sartre's native predisposition to think of subjectivity as central: a conscious person is always immersed in a world where his or her task is to make himself concrete. A "person" is not an unchanging, central essence, but a fluid construct that continually re-arises as an interaction among a person's consciousness, his physiology and history, the material world, and other people. This view itself supported Sartre's vision of people as fundamentally both doomed and free to live lives of commitment and creativity.
As Søren Kierkegaard, the earliest existentialist, wrote: 'I must find a truth that is true for me . . . the idea for which I can live or die.'—Problems of absurd life
Compared to other philosophies
La Nausée allows Sartre to explain his philosophy in simplified terms. Roquentin is the classic existentialist hero whose attempts to pierce the veil of perception lead him to a strange combination of disgust and wonder. For the first part of the novel, Roquentin has flashes of nausea that emanate from mundane objects. These flashes appear seemingly randomly, from staring at a crumpled piece of paper in the gutter to picking up a rock on the beach. The feeling he perceives is pure disgust: a contempt so refined that it almost shatters his mind each time it occurs. As the novel progresses, the nausea appears more and more frequently, though he is still unsure of what it actually signifies. However, at the base of a chestnut tree in a park, he receives a piercingly clear vision of what the nausea actually is. Existence itself, the property of existence to be something rather than nothing was what was slowly driving him mad. He no longer sees objects as having qualities such as color or shape. Instead, all words are separated from the thing itself, and he is confronted with pure being.
Carruth points out that the antipathy of the existentialists to formal ethical rules brought them disapproval from moral philosophers concerned with traditional schemes of value. On the other hand, analytical philosophers and logical positivists were "outraged by Existentialism's willingness to abandon rational categories and rely on nonmental processes of consciousness."
Additionally, Sartre's philosophy of existentialism is opposed to a certain kind of rationalistic humanism. Upon the confession of the Self-Taught Man as to being a member of the S.F.I.O., a French Socialist party, Roquentin quickly engages him in a Socratic dialogue to expose his inconsistencies as a humanist. Roquentin first points out how his version of humanism remains unaffiliated to a particular party or group so as to include or value all of mankind. However, he then notes how the humanist nonetheless caters his sympathy with a bias towards the humble portion of mankind. Roquentin continues to point out further discrepancies of how one humanist may favor an audience of laughter while another may enjoy the somber funeral. In dialogue, Roquentin challenges the Self-Taught Man to show a demonstrable love for a particular, tangible person rather than a love for the abstract entity attached to that person (i.e. the idea of Youth in a young man). In short, he concludes that such humanism naively attempts to "melt all human attitudes into one." More importantly, to disavow humanism does not constitute "anti-humanism".
The kind of humanism Sartre found unacceptable, according to Mattey, is one that denies the primacy of individual choice. . . . But there is another conception of humanism implicit in existentialism. This is one that emphasizes the ability of individual human beings to transcend their individual circumstances and act on behalf of all humans. The fact is, Sartre maintains, that the only universe we have is a human universe, and the only laws of this universe are made by humans."