Five thousand people a day are going to see the new Bacon retrospective in Paris, the city which the artist always thought of as his mecca. Here, the show's curator reflects on the contradictions and the mystery in the work

Francis Bacon was an old-fashioned militant atheist who always seemed to be looking for pretexts to issue a reminder that God was dead and to bang a few nails into his coffin. Nevertheless, Bacon's paintings - especially the big triptychs - tend to have a structure and an atmosphere which make them look as if they belonged in churches. Within the tradition of European religious painting God appears, of course, in numerous guises - as creator, as vengeful judge, as merciful father, as the son sacrificed and reborn, as king of the universe, and here as dead and gone. So Bacon's art has a momentous quality that has won him a widely perceived role as something like a successor to Picasso; it's not his formal qualities that have given him this exalted place but his creation of images that are seen as apocalyptic.

He himself said: "Really, I think of myself as a maker of images. The image matters more than the beauty of the paint ... I suppose I'm lucky in that images just drop in as if they were handed down to me ... I always think of myself not so much as a painter but as a medium for accident and chance ... I think perhaps I am unique in that way, and perhaps it's a vanity to say such a thing, but I don't think I'm gifted; I just think I'm receptive ..." This extremely sophisticated, intellectually acute man, with a deep realism about life, saw himself as a prophet.

While allowing that "the image matters more than the beauty of the paint", Bacon felt that painting tended to be pointless if the paint itself were not eloquent. He aimed at the "complete interlocking of image and paint" so that "every movement of the brush on the canvas alters the shape and implications of the image". All sorts of ways of putting paint on and taking it off were used to bring into being something unforeseen; it was a question of "taking advantage of what happens when you splash the bits down". Painting became a gamble in which every gain made had to be risked in the search for further gain. Winning, as always, was largely a question of knowing when to stop. For many years Bacon hardly ever stopped in time.

We walk into a bar or a party and suddenly people are there occupying spaces we might have moved into. They surge up in our field of vision and every movement they make seems to set off vibrations that impinge on us. They are expansive, anarchic presences, and we cannot avoid paying attention to them.

A similar raw immediacy emanates from the figures in Bacon's paintings. And with it a smell of mortality. But also an easy grandeur which suggests that they are demigods or kings.

These epic figures are mostly depictions of individuals in Bacon's life - his erotic life or his drinking life. Bacon had something of Picasso's genius for transforming his autobiography into images with a mythic allure and weight.

Was Bacon an expressionist? He didn't think of himself as one: "I'm just trying to make images as accurately off my nervous system as I can. I don't even know what half of them mean. I'm not saying anything. Whether one's saying anything for other people, I don't know. But I'm not really saying anything, because I'm probably much more concerned with the aesthetic qualities of a work than, perhaps, Munch was. But I've no idea what any artist is trying to say, except the most banal artists."

At the same time, he was convinced that "the greatest art always returns you to the vulnerability of the human situation".

FB: I was thinking about your bedroom - that just to have Holland blinds would be better aesthetically but that curtains make sex more comforting.

DS: Well, I'm sure curtains go very well with sex because they're there so often in pictures of sexual scenes. You yourself used to have curtains in your earliest pictures of having sex but now the backgrounds are starker and the sex seems just as good.

FB: Yes, but in the more recent pictures it's pure sex. You know, I don't really like the billing and cooing of sex; I just like the sex itself. Do you think that's a homosexual thing?

DS: No. I think it can go right across the board.

His choice of art: Egyptian sculpture. Masaccio. Michelangelo - the drawings above all, perhaps. Raphael. Velsquez. Rembrandt, mainly the portraits. Goya, but not the black paintings. Turner and Constable. Manet. Degas. Van Gogh. Seurat. Picasso, especially where he is closest to Surrealism. Duchamp, especially the Large Glass. Some Matisse, especially the Bathers by a River, but not wholeheartedly: "he doesn't have Picasso's brutality of fact." And Giacometti's drawings, but not the sculpture.

His choice of literature: Aeschylus. Shakespeare. Racine. Aubrey's Brief Lives. Boswell's Johnson. Saint-Simon. Balzac. Nietzsche. Van Gogh's letters. Freud. Proust. Yeats. Joyce. Pound. Eliot. Heart of Darkness. Leiris. Artaud. He liked some of Cocteau but generally had a positive dislike for homosexual writing, such as Auden and Genet.

Bacon was almost the only important artist of his generation anywhere who behaved as if Paris were still the centre of the art world.

Even today Bacon is widely thought of as an artistic leper. People like to say complacently that they are afraid to go near the work. They decline to cope with its "violence". Well, of course, Bacon's work is violent, in the sense that a Matisse or a Newman is violent in the force and incisiveness of its impact: it is aesthetically violent. ("I think that great art is deeply ordered. Even if within the order there may be enormously instinctive and accidental things, nevertheless I think that they come out of a desire for ordering and for returning fact on to the nervous system in a more violent way.") But the main objection that seems to emerge from the muddy controversy about Bacon's violence is that it is something more specialised - that it's a "morbid" taste for real violence.

There is certainly a very convulsive quality in many of Bacon's figures, and convulsion is a sign of violence. But not necessarily of a horrific violence. Convulsions of sexual pleasure are something most of us undergo as often as we can.

In the monumental spaces of the retrospective at the Centre Pompidou the balance of power in Bacon's work between convulsion and order seems remarkably different from what it has previously seemed (and will no doubt seem again in other installations). Here the dominant attributes are grandeur and calm.

Some peculiarities of Bacon's paintings:

(1) They are intended to be seen through glass - always, not just when they are partly in pastel.

(2) All the extant canvases are upright in format, with two exceptions; all others with a landscape format are triptychs.

(3) There is normally a single mass on a canvas unless it depicts a couple coupling and coalescing into a single mass.

(4) Human beings are always shown on roughly the same scale: the small canvases depict heads and these are about the same size as the heads on the figures which the big canvases depict - about three-quarters life- size.

(5) Even when the space is a perspectival stage in the Renaissance tradition, there are often elements such as arrows or dotted lines which are clearly not meant to be read as parts of what is depicted but as diagrammatic signs superimposed upon the image. Another indicator of the work's artificiality is a dichotomy between the handling of figures and that of settings: the figures are realised with highly visible brushmarks, the settings with a flat layer of thin paint.

(6) The paintings have titles like Study from the Human Body, Study for Portrait, Study for Crouching Nude, Study of a Figure in a Landscape, Study after Velsquez's Portrait of Pope Innocent X. So there are studies from, studies for, studies of, studies after, as if to say that at least some of the works were preliminary sketches for more definitive statements. What is in fact being said is that the artist wishes all his works to be regarded as provisional.

According to a curator's wall text at the Tate, "Bacon's view of existence strips life of purpose and meaning". So much for wall texts. Bacon's view of existence was that life was not empty merely because it was bereft of an afterlife and a deity. "We are born and we die, but in between we give this purposeless existence a meaning by our drives." The paintings are a huge affirmation that human vulnerability is countered by human vitality. They are a shout of defiance in the face of death.

"And what about the great silent figures of Aeschylus?" he suddenly said one day, apropos of nothing.

The Aeschylean menace and foreboding, the feeling - despite the humanism - of the immanence of higher and decisive powers, are there all of the time.

! 'Francis Bacon', organised with the collaboration of the British Council, continues at the Centre Pompidou, Paris (00 33 1 44 78 12 33), to 14 Oct (not Tues). On 28 Oct, the exhibition will open at the Haus der Kunst, Munich (00 49 89 21 12 70), to 31 Jan 1997. David Sylvester's 'About Modern Art: Critical Essays 1948-96' (Chatto & Windus, pounds 25) is published on 25 Jul.

Prophet and maker: Francis Bacon, top left, in his studio, created images that have been seen as apocalyptic. Left: 'Painting' (1946)

Atheistic trinity: paintings such as 'Triptych May-June 1973' (above) look as if they belong in churches