A free man in Paris: He couldn't speak French but post-War Paris was the making of Ellsworth Kelly. Iain Gale found out why

'Paris, Ernest Hemingway observed, 'is a movable feast. If you are lucky enough to have lived in Paris as a young man, then wherever you go for the rest of your life it stays with you.' That it has stayed with the painter Ellsworth Kelly is evident from the way he stares at the grey and orange plaster shell of Giacometti's studio, recently removed from Paris to the walls of the Tate Gallery. 'That's what Paris was like,' he says. 'That's the colour.' Having met at the Tate to discuss the room newly devoted to Kelly's work, we have wandered into an adjoining gallery to view the exhibition of art from Post War Paris. It is a happy diversion, which informs our conversation on Kelly's art, transporting us back 40 years to the Paris of the early Fifties where, as a young painter, Kelly, now 70, made the discoveries which were to direct his artistic development.

'It all started in Paris. When I got there in '48 I'd been painting the nude. Now I began to do portraits inspired by Picasso and Leger. I wasn't very articulate. What started it all was a need.' For the previous two years, Kelly had been a student in Boston, resuming painting studies interrupted by the war, and defining for himself a strong Expressionist style rooted in the brutal realism of Beckmann and Dix. He travelled to Paris on the GI Bill, a system of financial aid for young ex-soldiers by which each demobbed GI received dollars 75 a month for the length of time he had served, plus an extra 12 months. All that one had to do to qualify was register as a student. Quickly bored with Boston, Kelly (who had seen France as a soldier) chose to enrol at an art school in Paris, which was then unrivalled as the world capital of art. 'A lot of GIs did. Bob Rauschenberg was there and Cy Twombly.' Other ex-patriate American artists included Jules Olitski, Kenneth Noland and Sam Francis. Kelly's fellow future Hard Edge painter Jack Youngerman was a particularly close friend.

On his arrival, Kelly was drawn to the artistic hub of St Germain, where he lived in a number of hotels before settling on the Ile St Louis. Here he revelled in the impoverished life of a young bohemian. Nothing, it seemed, least of all the teaching at the Ecole des Beaux- Arts, had changed since the 19th century. Although he visited the bars of the quartier, frequented by Sartre, Camus and their acolytes, Kelly did not himself encounter much of the celebrated existentialist spirit of the time. It was not for want of trying:

'I didn't speak French very well. I remember seeing Genet sitting on a bench and so I sat down beside him. He got up. He wasn't going to have anything to do with me. So I followed him . . . We went down into a cellar bar. He was standing at the bar and I heard him ask, 'Qu'est ce qu'il fait?' ('What's he doing?') So I just said 'rien' ('nothing') and walked away.'

Rather than philosophers, Kelly's circle was made up of artists. Apart from the Americans he also knew the British artists William Turnbull and Eduardo Paolozzi, who lived nearby on the Ile St Louis. Contemporary French artists did not initially engage his attention. It was, rather, the city's artistic heritage which attracted him. 'I'd got interested in Byzantine art. I'd studied it in the museums. In Paris I visited the Louvre and the Musee Guimet.' The abiding fascination with the forms of religious art engendered by these studies is still present today in such works as the mandorla-shaped Untitled of 1988 (pictured top, with the artist). It was arguably, however, the work of a later French master which inspired what might be seen as the first of the colour-field paintings for which Kelly was to achieve international fame.

In 1952 he travelled to Giverny to visit Monet's house, which had not yet been opened to the public. While the house itself was fascinating, what had the greatest impact on him were the late paintings of waterlilies. 'It was fantastic. All the late paintings were still there. On the first day after I went there I painted a picture and it was solid green.' Kelly had laid the ground for his future development.

Three years earlier, however, he was still searching for a new direction. His interest in traditional work was tempered by an early respect for the more established Parisian constructivists. 'I was most attracted to Brancusi. I just called him up one day. And I got to know Vantongerloo quite well. But he was always lecturing about the need to explain his pictures according to geometry. It put me off. I hate geometry. I hate geometric painting.'

So, moving on, Kelly found a new mentor in Picasso and today, wandering through the Tate show, he stops before the artist's small, monochrome painting of 1945, Pitcher and Skeleton. 'In 1949 there was a big Picasso show at the Musee de la Pensee Francaise. A painting called The Kitchen was in it. It's the same kind of line work as this. It really influenced me a great deal. There's this thing in the curve. It's not so much painted out in The Kitchen. He paints up to the black line. The whole canvas is like when you take a piece of paper and crinkle it up. It all holds together. It's very tight. I was always attracted to Picasso because of the way he would construct. Picasso is very honest. He doesn't fake it. I learned a great deal from him about how to make things.'

Encouraged, Kelly began to look to other old masters of Parisian modernism, and in May 1949 he painted his first semi-abstract work, Toilette. Based on a urinal, it can be seen as a formalist homage to Duchamp, whose preoccupation with chance Kelly now began to embrace through an interest in automatism. Stimulated also by the Surrealists' use of the everyday, Kelly began to look around him at the fabric of the city itself. 'I wanted another way to compose a picture than me sitting down and saying, 'I'm going to make a picture.' I was looking everywhere for shapes.'

Enraptured by the pattern in the stones of the bridges and the high buildings, he produced a series of photographs and sketches - detailed studies of pavement grilles, chimneys and the bisected sides of houses. Talking in 1971 he recalled the revelation: 'It all belonged to me. A glass roof of a factory with its broken and patched panes . . . the shape of a scarf on a woman's head . . . paper fragments in the street.' Gradually Kelly's work began to incorporate these motifs, and an interest in the perceived, acquired at that time, has provided the basis for his art ever since. In the gallery his attention will move from a work of art on the wall to the wall itself and the surrounding architecture. 'Look at that doorway,' he enthuses. 'As you move it changes. I want my painting to relate to that. Is my painting as good as that? Does it work?'

This continual questioning is something else acquired in Paris. As we pass through the exhibition, Kelly repeatedly stops to apply his criteria to the works, some more familiar than others. 'These are really great,' he says of Artaud, some of whose work he remembers from the time. 'It's beautifully drawn. Worthwhile, genuine, approachable. It's the intention of the artist. You can feel it.'

Kelly is happiest in the room devoted to Giacometti, who he visited several times and with whose work he can empathise. Forty years ago, however, these sculptures seemed very different to his own work. 'His was very personal art and I felt very impersonal.' When, at a view at the Galerie Maeght in 1951, the sculptor remarked to Kelly of his painting 'C'est exactement la meme chose que je fait' ('That's exactly what I do'), the young man was at a loss. Now he understands the analogy. 'I've always said that the sculpture is the form and the ground is the space around it. All the negative shapes in a good sculpture are as strong as the form itself. This tall, thin one (Venice Woman VII) is fantastic. The space around it is vibrating.'

What Giacometti understood about Kelly's art was that, through his own experiments in 1949, the young American was himself making a similar exploration of the relationship between form and ground as that which animates the best sculpture. In November of that year Kelly visited the Musee d'Art Moderne and made a drawing, not of a work of art but of the windows. Worked up in the studio, this series of planes became his first painting to be made from juxtaposed panels.

'I wanted something in what I call literal space. It was the start of a new freedom. Everywhere I looked, everything I saw became something to be made. The forms found in the vaulting of a cathedral or a spatter of tar on a road seemed more valid and instructive and a more voluptuous experience than either geometric or action painting.'

Drawn to Paris by an artistic heritage which ranged from the Byzantine to Monet and Picasso, Kelly had discovered, in the physical actuality of the city itself, a unique art, based on the profound purity of perception. His words today still reveal the aspirations of the earnest young man who 40 years ago made his home by the Seine.

'Everything I look at in space is just fantastic. Most people look in order to stay alive. We get so used to looking that we don't investigate. When you really start to investigate it blows your mind. You have to stop thinking in a normal way and start investigating space. That's what my work's about. Seeing and vision. I want to capture some of that magic and mysteriousness. I've only just begun.'

Paris Post War, sponsored by the 'Independent' and supported by the French Embassy in London is at the Tate Gallery, Millbank London SW1 to 5 Sept.

The Ellsworth Kelly room at the Tate Gallery, London will be on view until October.

(Photograph omitted)