Architecture: Hush now, even concrete has feelings - Louis Kahn searched for souls in buildings and talked to bricks. Along the way he inspired some of the greatest Modern architects in the world. Paul Barker reports

WHEN Louis Kahn was struggling to design one of his last buildings in Ahmadabad, western India, he conducted a little Socratic dialogue: 'You say to a brick: 'What do you want, brick?' and brick says to you: 'I like an arch.' And you say to brick: 'Look, I want one, too, but arches are expensive and I can use a concrete lintel over you, over an opening.' And then you say: 'What do you think of that, brick?' Brick says: 'I like an arch.' '

Kahn, a Jewish American born in Estonia at the turn of the century, is one of the least-known, but most influential of the great Modern architects. He is also among the oddest. The dialogue was his way of working round from the automatic assumptions of early Modernism (concrete is always best) to his own wish, by the end of his career, to create 'very archaic- looking buildings'. Twenty years after he first made his mark, he was dead, killed by a heart attack in 1974 in the men's lavatory of Penn station, New York.

This year a major travelling exhibition of his work has given back to Kahn his place in history. But whether the exhibition will come to London remains unclear. British galleries are unsure of Kahn's appeal, even though without him there would be no National Theatre, no Lloyds building, no Pompidou Centre, no Hongkong and Shanghai Bank headquarters.

Kahn was an oddball, the kind of eccentric genius that the British might just take to heart. 'What did you do in the Thirties, Lou?' the British architect Alison Smithson once asked him. Kahn answered: 'I lived in a city called Le Corbusier.'

Even after he nudged out from under Le Corbusier's cloud, in the Fifties, he is said to have muttered to himself for the rest of his life: 'How'm I doin', Corbusier?'

Like Le Corbusier and Lutyens, he did his most grandiose work on the Indian subcontinent. For the new state of Bangladesh, he created a vast National Assembly at Dhaka. It is a kind of folly. A gargantuan homage to the Jeffersonian ideal now squats in the poverty-stricken capital of a country that has seldom known anything other than military dictatorship.

Kahn was exporting American values, in Classical dress. He himself was an undiluted example of the Statue of Liberty's 'huddled masses, yearning to be free'.

In 1906, at the age of five, he fled to America from Tsarist Estonia with his poverty-stricken Jewish parents. His face was scarred for life from falling into the fire as a child. His mother struggled in the rag-trade sweatshops of Philadelphia to keep the family off the breadline. When young Louis Isadore went to architecture school, he helped pay his way by playing the organ in movie houses.

All this, compounded by the workless years of the Depression, made him hesitant, unsure of himself. He always looked like a man who came up the hard way. He was short and unkempt, his tie always loose, his shirts wrinkled. He was painfully near-sighted.

He laboured over dim New Deal housing projects. He taught. But architecturally he did nothing of note before his Yale University Art Gallery Extension (1951 to 1953), begun when he was 50. He was one of Modern architecture's turning points, which paradoxically included a turning back from Modern to Classical. All his life he searched for a new 'order'.

He carried to extremes the architect's love of obscure, deeply meaningful remarks. 'Every building must have . . . its own soul,' he told his students. By the end, like Quinlan Terry or John Outram today, you feel that his preferred job would have been to rebuild the Temple of Solomon.

Some of his grandest and most successful projects were, indeed, temple-like. They housed art- or science-worshippers. His Kimbell Art Museum, at Fort Worth, Texas, enshrines the pictures beneath Romanesque vaults. His Salk Institute at La Jolla, California, is like a sun-baked monastery. Plain-walled zig-zagging labs flank a long piazza, interrupted only by a thin channel of water that leads the visitor's eye out to the Pacific, like a symbol of infinity.

In his 20 years of late-flowering creativity, he went through three different incarnations. Even more than late Corbusier, Kahn I was the great prophet of reinforced concrete, preferably decorated with wooden shutter-marks. At the Yale gallery extension, he started a fashion for deeply coffered ceilings. He loved to create high square silhouettes. This is Denys Lasdun's National Theatre to a T.

At the Barbican, however, you begin to see the influence of Kahn II at work - in the huge ducts for services that rise up through the Arts Centre. For Kahn II was the man who promulgated the theory of 'served' and 'servant' spaces in architecture. In practice, this meant the service ducts should become a separate, visible, part of the building. The baroque, tubey exteriors of Norman Foster's and Richard Rogers's most exuberant buildings, in Hong Kong, Paris and the City of London also follow this theory. They were both taught by Kahn.

Kahn was no functionalist. He admired the Baths of Caracalla in Rome (his favourite building) because the vaulting was 100ft high, when functionally 8ft would have done the job. At Fort Worth, he said, the wonderful thing about his art museum's open porches was that they were so unnecessary.

And there was nothing functionalist about his 'served' and 'servant' theory, first embodied in full force in his Richards Medical Research Building at the University of Pennsylvania (1957 to 1965). When Kahn was later mooted as the architect for an extension, the university's research scientists put their functionalist feet down. They had had too much trouble with mechanical faults, the air conditioning and the glare. This neatly foreshadowed the clash of opinions about Rogers's Lloyds: a wonderful addition to the City skyline, but disliked by the people who have to work in it.

Kahn III was the brooding architect of Dhaka and Ahmadabad. Here, he ransacked his sketches of Greece and Rome; he echoed the extraordinary constructions - many of them never built - by the 18th-century French architects of the Sublime, Boullee and Ledoux. Fortress-like walls were cut into by huge triangular and circular openings. Without Kahn III, we would have none of James Stirling's later, geometry-obsessed work.

Nikolaus Pevsner once said that architecture is that which makes beautiful ruins. The careful brickwork of Kahn's Indian and Bangladeshi structures is already crumbling under the sun. But never mind - they will make beautiful ruins. So will the National Theatre. Will Lloyds? Or the Pompidou Centre? We ought to know Kahn a little better.

A longer version of this article appears in the summer issue of 'Modern Painters' magazine.