The photographs of Brassai are absolutely not for those who think that Cartier-Bresson is the perfect photographer. Brassai is far from perfect, but, as an image-maker - and often an involved observer - he is far more interesting than his better-known French contemporary.
Not that Brassai was really French. Although his native Transylvanian village of Brasso is now in Romania, Gyula Halasz was born in Hungary in the last year of the 19th century, and took his professional name (in 1932) from his home town. After serving as a cavalryman in the Austro-Hungarian army during the First World War (he suggested a ballet to Bartok while on leave), Brassai went to study in Berlin. He arrived in Paris in 1924 and never returned to Hungary, although in 1937 he was awarded a gold medal, in absentia, at the Budapest exhibition to celebrate Daguerre's centenary.
It was only in 1926, with the encouragement of his fellow exile Andre Kertesz, that he switched from written journalism to photography, buying his first camera, a Voigtlander, in 1929 and graduating to a Rolleiflex in 1935. He soon became, in Jean Paulhan's memorable phrase, a man who "owns more than two eyes".
Lawrence Durrell has written a very funny account of being photographed by two young American press photographers. They leapt about athletically, shooting reel after reel of film, backed up by batteries of lights. Brassai, meanwhile, set up his rickety, collapsible tripod, got rid of most of the lights and took, after an hour's conversation in French, a single shot. "I want my subject to be as fully conscious as possible," he said to Durrell, "fully aware that he is taking part in an artistic event, an act." (Brassai would have enjoyed Evelyn Hofer's sublime rebuke to a fellow guest at a cocktail party who had observed that it must be wonderful to earn a living simply by looking at great buildings and going click, click, click. "Not at all," said Hofer, "I just go click.")
Brassai died at Beaulieu-sur-Mer in 1984, after completing a manuscript on Proust, and is buried in his beloved Montparnasse cemetery. He would have appreciated this month's huge celebration at the Hayward, which is accompanied by no fewer than three magnificent books: the catalogue (paperback £30, hardback £48) and reissues of two of his finest collections, The Secret Paris of the Thirties (Thames & Hudson, £16.95) and the masterly Paris by Night (Flammarion, distributed by Thames & Hudson, £29.95). The last is one of those great photographic books that looks just like they used to before black-and-white photogravure was virtually priced out of the market by cheaper, but barely comparable, offset printing.
Brassai could so easily have been a dilettante. Living in Paris between the wars and befriending Picasso, DalI, Genet et al, he could have been just another of the minor characters in cultural history. In fact, he was a considerable figure in his own right, more than proficient as draughtsman, sculptor (a touch of Arp, a bit of Modigliani, a lot of the Venus of Willendorf and even some Cycladic) and painter as well as journalist and photographer. He was also a wonderfully observant and trenchant writer. Apart from the great Richardson biography and Roland Penrose's study, the essential Picasso book is still Brassai's Picasso & Co. I was lucky enough to publish it and then meet the author in Paris in the late Sixties. Then nearly 70, he had all the energy and decisiveness of a much younger man.
While you always feel with Cartier-Bresson that he was a lucky man to whom those beautiful photographs just happened, an endless series of serendipities in black and white, with Brassai, you know that he almost willed his images into existence, precipitating and participating in them.
Given the relatively primitive mechanism of cameras in the 1930s (there were no motorised shutters in those days), and the long exposure times needed for ill-lit nocturnal pictures, the brothel photographs are astounding. One can understand the semi-posed head shots of pretty girls, appreciate the gentle mockery of the beauty parade downstairs, but one does wonder about his persuasive powers in one of the bedroom sequences: the man undressing; the heavy-set tart squatting on the bidet; the couple beginning to grapple on the bed. Each photograph is devastating in its immediacy - neither perfect nor imperfect, only unflinchingly honest. The whole sequence is, in fact, cinematic (Brassai made a film in 1955 which won a special prize at Cannes the following year).
In Picasso & Co, he quotes the Spanish master, to whom he has just shown a selection of his 1932-33 Paris underworld photographs: "When you see what you express through photography, you realise all the things that can no longer be the objective of painting. Why should the artist persist in treating subjects that can be established so clearly with the lens of a camera? It would be absurd, wouldn't it? Photography has arrived at a point where it is capable of liberating painting from all literature, from the anecdote, and even from the subject. In any case, a certain aspect of the subject now belongs in the domain of photography. So shouldn't painters profit from their newly acquired liberty, and make use of it to do other things?"
It is worth remembering that Picasso was no slouch as a photographer himself, and knew how to capture precisely the image he wanted before transposing it on to canvas.
One of my few criticisms of this great exhibition is the omission of what is possibly Brassai's finest picture of Picasso - the one he himself chose to introduce the photographic section of Picasso & Co, in which the painter looks more than usually menacing because he has bulked himself up in a thick, double-breasted suit over a sweater and a large woolly waistcoat. Not for the first time, Brassai makes him look positively sinister; he was always much too truthful to be a hanger-on, a complaisant member of Picasso's tertulia. Nor was he ever fooled by Salvador DalI and his preposterous wife, Gala. "He bore public witness to a veneration for Picasso," Brassai wrote of DalI, "an immoderate adulation which was only surpassed by his jealousy and unbridled hatred. It was intolerable that any artist other than himself could be considered 'the greatest Spanish painter'." Douglas Cooper at his bitchiest could not have been more vitriolic; one has to admire a man who could set so many of his contemporaries down so accurately, in words or photographs.
Without being unduly self-conscious, Brassai was professionally intensely self-aware. "I went so far as to prevent myself consciously from trying to 'compose' beautiful photographs," he wrote of the film he made. "I snuffed out the stills photographer in myself in remembering that the cinema is movement." On the other hand, I suspect he was merely coat-trailing when he observed: "Je n'invente rien, j'imagine tout."
One of his iconic images is the retired and manifestly successful old prostitute La Mome Bijou, whom he portrayed in several scrupulously adjusted poses and who, with her florid clothes and masses of heavyweight, flash costume jewellery, was said to be the inspiration for Giraudoux's 1945 play The Madwoman of Chaillot.
For those intellectual tourists in Paris who flock to the Cafe de Flore, nursing their cosy legend that this is where Sartre and de Beauvoir used to get in a few hours' honest scribbling before sorting out existentialism with their chums, it is almost shocking to come across them both, separately pictured in the cafe, smoking, thinking and, in the case of de Beauvoir, with pen on paper. Not legend at all: only literary history.
Overall, Brassai is as good with writers as with painters. His version of that vulgar old fraud Henry Miller is surely a defining one, as is his wonderfully revealing Jean Genet. Everything is there: the convict; the outsider; the massive brooding intelligence; the proletarian dress, with shirt sleeves almost brutally rolled up, leather belt twisted and the whole thing set off by the shirt bearing a neat, dandified little J G monogram.
If you want the archetypal image of the French working man, you need go no further than the market porter at Les Halles. If you want a bunch of lowlifes, he'll show you prostitutes and pimps who look like cliches from a Rene Clair film, until you realise that Clair almost certainly saw Brassai's photos first.
His photographs of artists as diverse as Matisse (sketching a nude model), Giacometti, DalI and Germaine Richier are the ones by which we will always know the originals.
Brassai could also be a bit of a wag when he wanted. His shot of a prostitute in Montmartre, carefully posed by a pool table, is another of his unforgettable icons. There she stands, in her rather coarse make-up and Louise Brooks haircut, her heavy breasts thrust out, lightly caressing the cue while the balls take up the foreground.
When he does a crime scene, with uniformed police, plainclothes detectives and children fishing all gathered round a dead body on the Seine embankment, you think of Weegee's New York police photos and you realise that Weegee was just a talented ambulance chaser, and Brassai an artist.
"Brassai: the soul of Paris" runs at the Hayward Gallery (020 7960 4242) until 13 May