Eve Arnold tells a story that neatly illustrates how her friend and mentor Henri Cartier-Bresson approaches the act of photography. "Henri intended to photograph Jeanne Moreau, who had just moved into a new apartment in Paris," she says. "He came in, greeted her, took one snap and left. And that was the snap they used. With many photographers it's a case of `just one more'. Not him."
As Cartier-Bresson approaches 90, a series of retrospectives, beginning tomorrow with Europeans at the Hayward Gallery, has collated more than 60 years of remarkable pictures: pictures that constantly surprise and engage, but which never resort to shock tactics, pictures of classical beauty but which are always suffused with spontaneity and joy.
As I talk to Eve Arnold in her London home, the admiration she feels for Cartier-Bresson is clear. And this is not the voice of some star- struck ingenue snapper but of the first American woman to become a member of Magnum, whose own work - her study of McCarthyism, her decade documenting Marilyn Monroe - is so vital and incisive.
"I first met him in 1954 in the Magnum offices," she says. "He was so generous: I shall never forget his kindness. In those years we all showed each other our pictures - he showed his as well - and it was a great example of what was possible. Before I went out on an assigment, I would go through some of his contact strips to set me up; not to copy him, but to see what was possible. It gave me a sense of joy. I and so many of us owe him such a debt."
Born in 1908 to an upper middle-class family, Cartier-Bresson soon developed a passion for painting. He studied under the theoretician of composition Andre Lhote, and was profoundly influenced by the Surrealists, but did not want to be bound by the dry academicism of the former, or by the latter's desire to fetishise every object. It was life that was thrilling for Cartier- Bresson, both living it and recording it: the challenge of grasping a reality that was, as he puts it, "continually vanishing".
This restlessness brought him to Africa in 1931, where he took his first photos, to Mexico and the States, to film-making with Paul Strand and Jean Renoir, to Spain. He was taken prisoner in 1940 but escaped and reached Paris to photograph the Liberation.
In 1947, together with Robert Capa, David Seymour and George Rodger, Cartier-Bresson formed Magnum, a loosely-structured co-operative picture agency, in which each member retained the copyright to the negatives. Capa was the adventurer, the gambler, the hedonist, while Cartier-Bresson was the cultivated introvert, the poet with a camera.
"These polar opposites created the agency," says Arnold. "It makes for a very vital operation." Cartier-Bresson's poetic style distils reality: his pictures are dense with meaning. The interplay of chance, form and alertness to the emotion of a scene (to which he is so uniquely sensitive) combines to define the "decisive moment". It's the axiom of his work, this collision of intellect and intuition. As he wrote in his 1952 book, The Decisive Moment: "Composition is the result of a simultaneous coalition, the organic co-ordination of elements seen by the eye."
That moment, for Cartier-Bresson, is a one-off: there can be no cropping, no retouching, no tampering to "improve" the geometrical relations in the picture. "He's a purist," says Arnold. "What he sees is what you get. He manages somehow to bind in nature: every move he makes, it's as if he had a dowsing stick."
It's difficult to escape an appeal to the mystical in his work - an awe at how he achieved pictures of such vigour and richness. Surrealism obviously provided an early influence, but it is perhaps Buddhism that sheds most light on his modus vivendi. In 1953, Zen and the Art of Archery by Eugen Herrigel was published in French. It breaks down the distinction between archer and target, subject and object - instead, to hit the target you must empty yourself. As Cartier-Bresson later wrote: "It is the photograph that takes you; one must not take photos."
An archaeology of his genius, however, does him scant justice: far better to see him at work. Arnold recalls a time in Paris walking with Cartier- Bresson and his wife Martine: "It was a brilliant summer's day and the artist Christos had wrapped Pont Neuf. Henri was photographing as he went. He was amazing to watch. Fleet and fast, like a ballet dancer. In one fluent motion the camera goes to the eye, he's clicked the button and he's down. Unless you were really looking for it you wouldn't know it was happening. It's a work of art."
It is this prowess, this ability to be so alive to his surroundings, to pounce and then to vanish, that accounts for the calibre of the street photography in the Hayward's Europeans exhibition and its 182 prints. Take "Pont de l'Europe, Paris, France, 1932", for example: a man is trying to jump a puddle; his heel is only a fraction above the surface of the water, and his attempt to keep his feet dry seems doomed to failure. As you look closer at the image, more and more geometric relations and compositional echoes emerge: the man's blurred body is reflected in the water; the ladder echoes the reflections of the railings in the water; the strips of curved metal in the water bear a resemblance to the reflection of the wheelbarrow. Finally, you notice the figure of a dancer in a poster, leaping gracefully in the opposite direction to the main subject.
"There's a legend about that picture," says Arnold. "Henri saw someone hop across the puddle and waited 24 hours until he got the exact moment again." But doesn't that detract from the purity of a unique moment? Arnold disagrees. "He shows you something you wouldn't have seen yourself," she says.
Cartier-Bresson's images do not just have a value in themselves: they are not abstractions of life but an engagement with it. As Arnold puts it: "His work is a kind of living history."
Which is not to say that his work offers social and political judgement. As he himself once put it:"I want to prove nothing, demonstrate nothing."
Although not as widely known as his photographs, Cartier-Bresson's drawings and paintings occupy an important place in his heart. Since the early Seventies, the Leika has been replaced to a large extent by the pencil. "He keeps saying that he's not photographing. It's not true!" reveals Arnold. "But he has said that people don't understand his photography if they don't know his drawings and paintings. He draws constantly: I went for lunch with him and he was sitting reading a newspaper, sketching, at great speed behind it. This instant recognition is in the same context as his photography. He doesn't set anything up, he doesn't say `Hold it'. It's fleeting and then it's gone. He has captured it for us. And when he works, it looks as if it he were put there for no other reason in the world than to take these pictures."
`Europeans' opens at the Hayward Gallery, London, tomorrow. `Tate Tete' opens at the National Portrait Gallery on 20 Feb; `The Drawings of Henri Cartier-Bresson' opens 6 March at the Royal College of Art
`Europeans', `Tate a Tete' (available 16 Feb) and `Line by Line' are published by Thames and Hudson