'The Cezanne on view in Paris is a complicated, uneasy figure, driven by anxiety as much as anything'

Paul Cezanne, the dyspeptic hermit of Post-Impressionist French painting, has been widely claimed as the patriarch of modern art. It has become almost conventional to view Cezanne as the founding father of a new, 20th-century way of seeing and thinking about the world - an artist whose achievements went beyond art, into science and philosophy. "Masterer of reality" was how the poet Rainer Maria Rilke described him, writing in 1907, a year after Cezanne's death. But was Cezanne truly the Einstein of painting? The large retrospective of his work, currently to be seen at the Grand Palais in Paris, later to arrive in London, leaves the question open.

The Cezanne on view in Paris is not quite the unruffled philosophic genius of modernist reverence - a figure who has, incidentally, quite a lot to answer for, certainly in this country, including thousands upon thousands of appalling student paintings of themes such as "The Faceted Apple", almost all the works of the Euston Road school, and the plumbline-and- squint method of drawing still being taught, remarkably, in certain British art schools today. The Cezanne on view in Paris is instead a complicated, uneasy figure, driven by anxiety as much as anything else.

The sheer scale of this exhibition has a necessarily humanising effect on its subject, revealing his weaknesses and oddities and the extent to which he had to struggle with the refractory nature of his own personality. Among other things, this serves to clarify the twofold paradox of Cezanne's position in the history of art: first, that someone who spent virtually his entire creative life rooted in a tiny patch of Provencal countryside should have come to be regarded as the pioneer of the first great urban 20th- century style of art (Cubism, so clearly prefigured in the work of Cezanne after 1880); second, that anyone whose art and personality were so inimitably weird should ever have seemed imitable to anyone else.

In his youth Cezanne was something of a malcontent, or at least a man who had intense feelings which he did not know what to do with. Emile Zola, who had been his best friend at school in Aix-en-Provence, included a lightly disguised portrait of the young Cezanne in his novel L'Oeuvre. Zola's caricature of Cezanne, Claude Lentier, is a painter torn "by his passion for the flesh of a woman, by his foolish love of nudity desired and never possessed, an impotence to satisfy himself. The women whom he drove away from his atelier, he adored in his paintings - there he caressed and violated them, desperate that through his tears he would not have the power to make them as beautiful and vibrant as he desired."

Cezanne acknowledged receipt of the novel from Zola with chilly curtness - "I thank the author for this kind token of remembrance and ask him to allow me to press his hand in memory of old times" - and never spoke to him again.

Cezanne was upset because he had indeed been Claude Lentier or someone very like him. His early work was unpleasant and unsuccessful, and it was dedicated, to a great extent, to the mental caress and violation of women. His first pictures contain almost no suggestion of his eventual destiny as a painter of landscapes and still lifes. Cezanne's most striking early essays in art are violent, quasi-mythological figurative works painted in unsuccessful homage to Gericault, Delacroix and Manet. Frequently depicting scenes of orgy and affray, they are muted, ugly, disturbing little things.

Le Festin, painted in the late 1860s, is characteristically bizarre. A dozen nudes, each made to look as if modelled by a child out of chewing gum, feast and copulate around a table under a blue sky full of writhing clouds. Hung close to it, Le Meurtre represents a gloomier, more morbid corner of the young Cezanne's temperament. It is a dark and thoroughly nasty picture, an image of the unexplained, motiveless killing of a woman. The colours are rancid, and the figures shaped like dumplings squeezed in the hand, entirely lacking in any sense of anatomical structure. In its dulled, nihilistic mood, the painting is faintly reminiscent of Goya's images of atrocity in The Disasters of War, but unredeemed by any sense of outrage.

Even the young Cezanne's few still life paintings seem shot through with dark passions and a potential for violence. The objects on the tabletop are defined with aggressive, hallucinatory clarity, each made so insistently separate from all the others that it seems to brood as well as simply be there. The handle of the knife protrudes over the table's edge, ready to be grasped. Below, encroaching shadows are dark and thick, as repellent as pools of blood.

Cezanne's transition from morbid fantasist to lucid student of reality is generally reckoned to be one of the most remarkable metamorphoses in the history of art. Cezanne himself gave much of the credit to Camille Pissarro, that earnest Impressionist observer of nature, who took him on a series of walking tours through the landscape of Auvers and Pontoise in the early 1870s. The experience persuaded Cezanne to turn his attention away from the murk inside himself and towards external reality. It must have been a great relief. In the earliest paintings which Cezanne produced under Pissarro's influence it is as if a temperament previously strained to the limit has been unstrung and suddenly relaxed. Cezanne's pictures of Auvers are quiet essays in a quiet Impressionist naturalism. They are sunny, neutral and dull.

Cezanne seems to have known that this would not quite do, and he began to find ways of breaking up his own Impressionist formula. He invented a new way of painting, beginning to suggest depth and model form through hatched, parallel brushstrokes that make the houses and hillsides and olive groves of his art seem to shiver and flicker and vibrate. Cezanne's view of nature suddenly became much less still: a mobile place seen by an implicitly mobile eye and temperament. The old, disturbing energy had re-entered his art, but this time under control.

One of the morals of this exhibition is that the young, passionate Cezanne was never quite suppressed by his older self. His most memorable work would be the product of a subtle, secret marriage between the two sides of his temperament. Cezanne's life after the mid-1870s was a prolonged struggle to reconcile his own most troubling feelings with the cooler demands of an art of observation. To pay too much attention to the facts of visual experience would make him a boring painter. To pay too much attention to the inexplicable, boiling inner self might make him a mad or incoherent one. These two extremes would represent the Scylla and Charybdis of his art. How much of himself, how much feeling, how much desire - and anger, violence and morbidity - could he put back into a form of painting ostensibly devoted to the study of appearances?

Cezanne's most successful answer to the question was his most distinctive innovation: the flickering second outline so often given to the shapes in his pictures. The slope of the Mont Sainte-Victoire - the mountain on to which his studio looked and which he painted so often - is never quite definite, always being complicated by this echo of itself. In one respect, this was an extremely logical device, one of Cezanne's ways of being true to the relativities of perception itself.

The slightly drunken effect of these double outlines duplicates the way in which objects jump when you look at a scene first with one eye closed and then the other. It was Cezanne's way of defining a new, relative sense of space in art, and his way of framing apparently simple conundrums actually fraught with the complexities of a Xeno's paradox. Which eye is telling the truth? Where, exactly, is the real Mont Sainte-Victoire? In the immediate aftermath of Cezanne's death, Picasso and Braque embarked on their years of Cubist experimentation. Provoked largely by the complexities of his art, they struggled to develop a new sense of space and form in painting. They felt as though they were "roped together like mountaineers". It was Cezanne's mountain that they were climbing.

The analytical uses to which Braque and Picasso put Cezanne's style have largely determined his place in history as the great peintre-philosophe of modern painting. This exhibition suggests that his right to that place in history is open to debate. True, Cezanne had given visibly persuasive form to two large modern ideas: the notion that all experience is relative, and the corresponding conviction that the spatial conventions of post- Renaissance perspective tell too simple a story of our perceptions and therefore need to be replaced. But these were not his ideas alone. They are there in Monet, for example, in French painting, and they had in fact been implicit in Western art since the time of Constable and Turner. Cezanne never made as vast a leap towards a new art as those English painters had done half a century earlier. He certainly formalised and clarified ideas that already existed in the culture of his time, and he certainly made others see those ideas more clearly than they had done before. But he did not invent them.

Cezanne's own art is subtly diminished, too, by insisting that his achievement was analogous to anything like a scientific theorem or philosophical proposition. It is still often said that he arrived at his way of painting through constant experiment and analysis rather than through anything as dirty and inchoate as feeling. But Cezanne arrived at his art through a storm of feeling, and his finest works are those that bear the scars. His best paintings are those where the sense of his art as a form of pseudo- scientific analysis - the dry and effortful web of thoughtful touches - has been punctured. They are not the register of Truth, but the register of Cezanne's humanity.

Part of the skill of the hang at the Grand Palais lies in its clever suggestions of the passions always simmering near the surface of Cezanne's art. Strange unsettling portraits of Cezanne's wife, Hortense, or his son, Paul, make the paintings nearby also seem to vibrate with the anxieties of human relationship. The cumulative implication of such juxtapositions is that Cezanne was never quite easy in himself. Every Mont Sainte-Victoire is also a Vesuvius.

Cezanne was often tremendously morbid, particularly when he painted his famous apples on tablecloths. Such pictures were not only his way of upsetting the applecart of academic expectations, subversively implying that a picture of fruit could be as profound as any Venus Anadyomene - "I want to stun Paris with an apple," he once said. They were also, impicitly, equivalences for some of the sadness of existence. Cezanne's apples are painfully isolated, blooming with life but also surely decomposing. Their force is the force of feeling and their true subject is Cezanne's sense of mortality.

Cezanne's apparent studiousness was a mask for self-expression. Intense observation, particularly in late Cezanne, very easily shades into something close to intense identification. His work seems much closer to that of Van Gogh, nowadays, than perhaps it has ever done in the past - and if every Van Gogh sunflower is a self-portrait, something similar is surely true of Cezanne. The mountain incandesces in the sun like an emotion made concrete. The fir tree shivers in agitated air like a fear or wish made palpable. The apple rots. The skull stares.

n 'Cezanne' runs at the Grand Palais, Paris, until 7 January 1996 (00 331 44 13 17 30) and at the Tate Gallery, London SW1, from 8 February to 28 April 1996 (0171-887 8727)

n An 'Omnibus' Special about Cezanne will be broadcast on BBC1 to coincide with the Tate exhibition. BBC2 will broadcast a 'Trilogy' and a series of 90-second short films about the painter in February

Cezanne as others saw him...

"He was afraid of women... He never brought girls back to his place. 'I can't have women around,' he used to say, 'they disturb my life too much. I don't know what they're for, and I've always been afraid to find out' "

Emile Zola

"I do not believe that a case like Cezanne's is to be found in the whole history of art. Think of his living to the age of 66 and, from the first day, he took a brush in his hand - remaining as isolated as if he were on a desert island"

Auguste Renoir

"The next generation may speak of Cezanne's portraits as the art of the trowel rather than of the brush"

George Moore

"The first wild man of modern art"

Roger Fry

"History must needs describe Cezanne as un grand rate, an incomplete giant... Cezanne was fated, as his passion was immense, to be immensely neglected, immensely misunderstood, and now, I think, immensely overrated"

Walter Sickert