ART / Something out of nothing: 'Paris post-War', sponsored by The Independent, opens on Wednesday. Andrew Graham-Dixon argues that existentialism is not so much a philosophy of life as a school of art

The Bible of existentialism, Jean-Paul Sartre's Being and Nothingness, was published in occupied Paris in 1943 as a fat, fat paperback in an edition of 2,000. No one reviewed it, and hardly anyone seems to have read it. The pattern was set: Being and Nothingness would become possibly the most influential unnoticed and unread book of the 20th century. Even now it seems unlikely that many people have read its 650 or so pages from start to finish (not counting professional philosophers). This is not surprising, given the fantastic opacity of the prose in which it was written.

Here is Sartre, in Being and Nothingness, on the subject of 'temporality': 'A For-itself which has squeezed out all its nothingness and been reapprehended by the In-itself, a For-itself dissolving into the world - such is the Past which I have to be, such is the avatar of the For-itself. But this avatar is produced in unity with the appearance of a For-itself which nihilates itself as Presence to the world and which has to be the Past which it transcends. What is the meaning of this upsurge?' What, indeed?

All this might make 'Paris Post-War: Art and Existentialism 1945-55', at the Tate Gallery, seem a somewhat perverse exercise: an attempt to establish the links between a philosophy that no one has ever fully understood and an art whose precise meanings have never been agreed; an absurd effort to define the culture of the Absurd.

But what the show demonstrates, with some conviction, is that the best way to understand existentialism is, indeed, through the work of the artists - most notably, on this showing, Giacometti and Dubuffet - who were influenced by its knotty complex of ideas and attitudes. This show might even be said to prove that existentialism was not, strictly speaking, a philosophy at all, but an outlook on life, a way of thinking about what it means to be a living human being.

Sartre himself had already tacitly recognised this by formulating the existential attitude first in a novel, Nausea, written in 1935, rather than in a philosophical text. Nausea, as its title suggests, defined existentialism less as a network of coherent beliefs than as a vague and amorphous attitude of disgust; a sickness with the self, and with the world, that would assume the status of a creed, since for many it came to seem the only appropriate response to things in the disaffected climate of the post-war years, in the aftermath of the discovery of the true extent of the Nazis' atrocities and the unthinkable destructiveness unleashed by the Bomb.

Existentialism was a philosophy rooted, not in logical argument, lucid rationality, but in emotional despair. I think dark thoughts, therefore I am. 'At this very moment - this is terrible - if I exist, it is because I hate existing,' notes Roquentin, the narrator-hero of Nausea. 'Hatred and disgust for existence are just so many ways of making me exist, of thrusting me into existence.'

The narrator-hero of 'Paris Post-War' turns out to be Giacometti, whose work rightly occupies the large gallery at the heart of the exhibition. Here the sculptor's attenuated, divining-rod figures stand to attention, a forest of thin human trees. They make the space that they occupy seem immense and their theme seems, indeed, to be less the figure than the air that surrounds it. This is art predicated on a dizzying form of agoraphobia. Giacometti gave visible form to the existential attitude, creating likenesses of the human form suspended, literally, between being and nothingness: images of people on the brink of disappearance into thin air, painfully alone in the world and terminally separated from each other.

Existential alienation has become one of the emotional cliches of the later 20th century, an attitude that has been struck so often, by so many fifth-rate artists and writers and rock singers striving to seem soulful and serious, that it may have been terminally cheapened.

One of the great problems of the modern world (which evokes certain parallels with the world that spawned existentialism) is the sense that, faced with appalling political events such as those unfolding in Eastern Europe at the moment, the language of revulsion has been somehow used up, weakened by so much insincere mimicry of its once salutary rage. But to look at Giacometti's sculpture (or to read Sartre's writing) is to sense the urgency and outrage that lay behind the existential attitude, the vitality and profundity of its depression, with renewed force.

Sartre himself recognised, perhaps, that Giacometti's sculpture had defined the existential outlook on the world better than words could ever do. Looking at these thin, isolated, anonymous figures, these anti-monuments created for a world that no longer seemed to deserve or merit the grandeur and self-confidence of monumental statuary, he noted his impressions: 'Between things, between men, connections have been cut; emptiness filters through everywhere, each creature secretes his own void.'

The alienated gaze of Nausea's Roquentin would find other equivalents in the art of Artaud and Fautrier and Michaux, whose inchoate imagery - this exhibition is thronged with their tiny and indistinct drawings made of hallucinatory scribbles and scratchings and blots - suggests a world where things constantly resist precise description and fight against representability. A world where vision, itself, has become a virtual impossibility, where objects have suddenly become so hostile to man that it is impossible to distinguish between perceptions and apparitions.

Dubuffet turned paintings into dumb, thick walls of pigment, churning viscous fields from which emerge mad infants and village simpletons and heavy-limbed gods and goddesses: pictures that are both violent and subversive. Their pittings of dense matter against the scrawled imagery that struggles into visibility out of it are charged with metaphorical intent. They suggest that the fictional and mythical worlds we have invented out of the thick and impenetrable actual world that surrounds us are no more real or convincing than the imaginings of an idiot child.

'All of a sudden,' Roquentin finds in Nausea, 'the park emptied as if through a big hole, the world disappeared in the same way it had come, or else I woke up - in any case I could not see it any more; there remained some yellow earth around me, out of which dead branches stuck up in the air.' Existential doubt, perceptual hesitancy and hallucination became the impetus behind a certain kind of abstract art. Sartre championed the cause, in particular, of Wols, a bedridden alcoholic, with an inflated reputation for mysticism, who produced inflamed doodles by the score before his premature death (not from drink but food poisoning).

The primary weakness of 'Paris Post-War', which may stem from a perennial curatorial over-eagerness to proselytise the causes of forgotten or barely known artists, is that the artists which this exhibition sets out to rediscover would, almost to a man, have been better left languishing in obscurity. Francis Gruber's mannered, miserabliste paintings of skinny men and women living on the poverty line in barely furnished interiors are dull and exhausted footnotes to a played-out tradition of expressionist painting with a social conscience.

Jean Helion's exercises in hallucinatory surrealism are ineptly painted fantasies that aim to conjure the oddness of life as seen through the eyes of Sartre's Roquentin but strain so hard to be weird that they end up seeming curiously matter-of-fact and unimaginative. The abstract paintings of Bram van Velde are not only dull and dark and incompetent, but bear virtually no relationship to the show's theme.

Four paintings by Picasso just about rescue the exhibition from the inclusion of these three hopeless mediocrities. They also complicate the premise of the exhibition itself, because although these pictures - painted in the sombre, linear, monochrome manner that Picasso adopted during the post-war years - can hardly be said to have been inspired by existentialist philosophy or literature, they can be said to incarnate the existential view of things. Skulls grin and candles gutter in stark interiors; the paintings are mementi mori and the way Picasso uses line, so insistently, makes pictorial structure itself seem skeletal, angular, full of a sense of death and of despondency made palpable.

Picasso's pictures relate both to his own earlier work, so perpetually morbid, as well as to the work of Goya, whom he had so often invoked in his paintings of the war and post-war years (it is a shame that this show could not have also included The Charnel House). The presence of his pictures here, and the way they echo other paintings painted in another time, quietly suggests that existentialism may itself have been the reformulation of an old human response to catastrophe and doubt.

Political disillusion and a sense of nihilism might have seemed, in post-war Paris, to have been tinged with radical newness. But Picasso quietly provides existentialism with a history, speaking of despair and alienation in a voice that recognises other, older voices.

'Paris Post-War: Art and Existentialism 1945-55' at the Tate Gallery from 9 June to 5 September. Sponsored by The Independent and supported by the French Embassy in London

(Photograph omitted)