Those books revealed a forgotten world in which architecture was garish, clever, witty and inventive. Where neon and stone came together, where billboards and signs became architectural. It felt modern. Not modern in the way architects usually mean it -- shiny and mute -- but modern in a way that seemed to capture the multifaceted and complicated experience of contemporary life. It was an architecture that was interested in the unarchitectural mess of the rest of the world.

It was partly through those cheap books that I got to know the work of Robert Venturi and Denise Scott Brown, the architects most closely associated with Postmodernism in architecture. Venturi had first received acclaim for the Vanna Venturi House (1961--4) designed for his mother and the 1966 book Complexity and Contradiction in Architecture, in which he argued for an architecture based on humanistic responses to the diverse issues that buildings must address, rather than the highbrow theoretical pretension that was prevalent at the time. In 1972 Venturi teamed up with Scott Brown and Steven Izenour (who died in 2001) to publish Learning from Las Vegas. It was an attempt to explore and understand a place which was all the things that proper architecture shouldn't be. It used empirical research methods, drawing on media studies, Pop art and social science as ways of understanding a new kind of urban phenomenon. It suggested that ordinary and everyday places such as supermarket parking-lots, the roadside commercial strip and casino advertising were a resource from which architects could learn.

The book also introduced a new definition of architecture as either a 'Duck' or a 'Decorated Shed'. The Duck -- a term inspired by a duck-shaped duck restaurant in Riverhead, Long Island -- describes buildings that are sculptural objects. This includes all those fast-food kiosks in the shape of doughnuts and motels with concrete teepees as rooms, but also almost all modernist architecture, designed as an abstract object in relation to the local context. The Decorated Shed is a low-cost box with a huge sign on top. While Ducks might have garnered the newspaper column-inches and the big budgets, Decorated Sheds have proliferated across the landscape in the form of IKEAs and Office Worlds. 30 years after Learning from Las Vegas nothing much has changed -- except maybe the Ducks are more often Peking Ducks, shredded and scattered like Frank Gehry's Guggenheim Bilbao -- and the book remains one of the most important architectural studies of the late twentieth century. Venturi, Scott Brown and Associates, Inc.'s contribution to architecture has been to broaden the field, embracing everything from fine art to urban geography. And they have built projects that have been both highly controversial and influential. But despite all this they, along with Postmodernism itself, have managed to end up as far out of step with mainstream architectural culture as it is possible to be.

There's a reason for this. When it comes to architecture, the term 'postmodern' was defined by the worldly-critic-turned-cosmic-gardener Charles Jencks. His book The Language of Postmodern Architecture (1977) extended the use of the description from literary criticism to architecture and the visual arts. In doing so it patched together a whole range of people and projects into a seemingly coherent movement. But while his study was an attempt at definition, it necessarily reduced the scope, depth and variety of the approaches it covered. It wasn't long before Postmodernism became synonymous with little more than a Pop use of classical architecture and a general tendency to mash together various historical styles. After years of exploitation by corporate architects during the 1980s it was no longer an intellectual idea, just a much-despised aesthetic.

So when I met Venturi and Scott Brown in their hometown of Philadelphia I thought I had been presented with a rare opportunity to declare and share my love of Postmodernism. But my confession didn't elicit the response I had expected. In fact it prompted Venturi to declare me a 'degenerate' and a 'pervert'. Which, to most architects, is like being called a loser by a gambler who put everything on red when it came up black.

It turns out that not even Venturi and Scott Brown want to call themselves postmodern architects. They deny it as if they were suspects at the McCarthy trials. Instead, they claim to be early modernists, but also (with a twinkle in Denise's eye) note that Freud wasn't a Freudian. On their website Robert Miller responds to the common assumption that they unleashed Postmodernism by denouncing it as 'a charge comparable to calling Thomas Edison the father of disco'.

The great big glowing heart of VSBA is Pop. And their idea of Pop is wide and deep. It's the Pop of neon signs on the Vegas strip, but it's also the soapbox-Pop of grassroots community campaigns. While they were studying the glowing casino neons of the Nevada highway, they were also working to save a pedestrian strip in Philadelphia, helping to preserve a community threatened by the construction of a new highway. Indeed it was just this type of cause that first brought them together: they met at a University of Pennsylvania faculty meeting where Denise was arguing against a plan to demolish the university's Frank Furness-designed library. Later, they pioneered preservation planning for historic districts in Galveston, Texas, and Miami Beach, Florida. Theirs is a kind of socially engaged Pop -- a Pop that isn't only fast, fun and ironic, but political and moral as well.

Learning from Las Vegas looked at an extreme situation in an attempt to understand more common situations. Other projects, like 'Learning from Levittown' (which was started in 1970), looked at more ordinary situations. Like Learning From Las Vegas, the Levittown project emerged from Venturi and Scott Brown's teaching at Yale. It was an exploration of both developer housing and the way that it was occupied -- a mixture of anthropology, sociology and home-decoration tips. Here, projects connected with stories, traditions and imagery from the contemporary vernacular: a kind of folk-Pop. It made me think of the artist Jeremy Deller's description of the difference between Pop and Folk art: 'Warhol said that Pop art was about liking things, whereas for me Folk art is about loving things'. And perhaps it's this idea of making architecture (and architects) engage with the world that surrounds them -- rather than with a theoretical model, a diagram or an imaginary Utopia -- that drives Venturi and Scott Brown's Pop sensibility.

Of course, their Pop-art credentials are pretty good. While she was a student at London's Architectural Association, Denise knew of the Independent Group -- the members of which included Eduardo Paolozzi and Richard Hamilton who were hunched around John McHale's suitcase-full of shiny American magazines, chopping and gluing them into proto-pop images. Andy Warhol went to the opening of Venturi and Scott Brown's 1976 Signs of Life: Symbols in the American City exhibition at the Smithsonian Institute. And the architects took their students to visit Ed Ruscha before going on to study Las Vegas.

Ideas overlap too. Venturi and Scott Brown are interested in 'flatness' like Jasper Johns. 'Baroque architecture needed a depth of one yard to do its decoration', they write, 'Renaissance architecture perhaps a foot, Rococo one centimetre, and Art Deco could suggest seven or eight overlaid surfaces in one bas relief, one centimetre deep. We loved the richness within the Deco low relief, but when we came to think about what this meant for us today, we realised that our decorative surfaces should be two-dimensional -- for many reasons, including cost.' Like Alan D'Arcangelo and Ed Ruscha, they are interested in signs. Indeed, their thinking about signs led them to think about architecture that didn't look like the strip but still acted like signs. Signs of Life, for example, explored the invisible signs of domesticity. It showed that ordinary contemporary homes were actually dense collages of meaning. And that building materials are not just things to keep the rain out; they are also signs that, in the exhibition, quite literally speak. Speech bubbles burst out of houses: clipped bushes whisper 'formal colonial garden', curtains say 'Colonial Convivial', sofas speak of 'Neo-Regency Elegance'. The project is a kind of anthropological version of Richard Hamilton's Just What Is It That Makes Today's Homes So Different, So Appealing? (1956).

Learning from everyday life is embedded in the way that VSBA's work. Their office is located on exactly the 'almost alright' kind of Main Street they write about. The building is a converted 'generic loft' and their professional life blurs into their domestic life. The ground floor of their home is like a quirky museum of Americana, Pop art, Folk art, and adverts: from the drive-in McDonald's sign in the hallway to the oversized ketchup bottle, the papier-mache cactus and the stencilled paint patterns. All within a leafy arts-and-crafts setting.

Contemporary architecture is a branch of the entertainment industry. Buildings look like a freeze-frame of a special-effects-rich Hollywood movie: dynamic explosions of glinting titanium and glass. In complete contrast, VSBA make what they call 'buildings that look like buildings'. And they really do. There is something very odd about looking at a VSBA project. They don't do the things that your eyes have come to expect from contemporary architecture. There is no structurally engineered sleight-of-hand, no sensation of weightlessness or aspiration to transparency, and no funny shapes.

What there is is something that isn't embarrassed to look like a building. From the giant scoreboard-as-facade of the unbuilt National Football Hall of Fame, to the gilded TV antenna at the top of the Guild House (1961--66) -- a residential accommodation for elderly people -- which they describe as 'as a symbol of the aged, who spend so much time looking at TV'; from the 'ghostly' outline of Benjamin Franklin's house -- part of a museum and memorial to Franklin on the site of the home he built himself -- to the proposal for the U.S. pavilion at the Seville Expo with its facade as a huge Stars and Stripes, frozen mid-flutter, it is architecture forced though a concept -- an idea driven into built form.

Despite their love of the messy vitality of the commercial, there is a kind of joyful restraint in VSBA's work. As they took me around their office they described a series of designs for university buildings. They became more and more excited about how 'boring' the projects were. It's certainly out of sync with the decadent excess of contemporary architecture, which tries to look as unlike a traditional idea of a building as possible.

Denial is an underrated part of the design process. Their refusal to over elaborate, their interest in working with cheap buildings, the importance they ascribe to appropriateness echoes elements of New Brutalism - the architectural movement named by Reyner Banham and practised by Independent Group members such as Alison and Peter Smithson, and James Stirling. The idea of architecture as a basic shelter is reflected in their passion for the 'Decorated Shed' and the 'Generic Loft'. And perhaps it's this love of the authentic, pragmatic, industrial building that really links them to those early modernists who admired and learnt from the American industrial vernacular.

With some self-awareness, they say that their architecture is a little hard for people to take. And it's not difficult to see why. A recent small-building project for the 1998 Acadia Summer Arts Program is perhaps the most challenging piece of architecture since Mies van der Rohe's iconic 1929 Barcelona Pavilion. It transforms the A-framed vernacular building form into a giant bit of communication -- a capital 'A'. Jaunty mini letters 'r' and 't' are propped up on sticks to spell out 'Art. It is incredibly precise, very vulgar and direct, very small in scale and budget, but BIG in idea. Its reductiveness has something Miesian about it; it represents an editing of the redundant architecture, paring it down to a vital relationship between the conceptual idea and its physical manifestation.

VSBA's design for the Sainsbury Wing extension to the National Gallery in London (1988--91), which was constructed during an era of deep division between traditionalists and progressive modernists on the British architectural scene, best illustrates how their work has been misunderstood. Because it used historical references, it was assumed to be on the side of the traditionalists -- at the time marshalled by Prince Charles. And consequently, those architects who had argued for progressive modern architecture slammed the extension. But they must have failed to see the real point of the project.

Just watch as the facade of the extension responds to the boring neo-classical National Gallery facade and the civic space of Trafalgar Square. As the extension kinks round, replica pilasters pile up like the Keystone Cops going around a corner and the rhythm of the National Gallery facade breaks down in a chaotic clatter, like a drummer having an epileptic fit. Then the facade fades into stone blankness, like the front of something important and bureaucratic -- maybe a bank or a ministry, expensive, abstract and faceless. Meanwhile, a big hole is cut into the facade. The kind of big hole that lets lots of people in and out. A hole that you might find in the front of a cinema or a supermarket. The facade starts to look more like a petrified billboard -- a stone version of the Piccadilly Circus neons. It's saying that it is modern, not pastiche. The design plays with codes and expectations, using construction techniques to hold things up and make social comment. Faced with wit, irony, love and care, it's no wonder that British modernists got confused. Architecture doesn't usually do that kind of thing. Modern architecture has to look modern. And modern is a narrowly defined range of things. It's capital M modernism or an aesthetic that is derived from it. It's not modern meaning NOW! It's an ideology, not a feeling. Ultimately, the Sainsbury Wing wasn't a building that was for or against anything -- except lucidly embracing the complex demands and situations of its context in an explicit way.

Venturi has written a kind of poem-polemic that summarises his position. Its called 'A Disorderly Ode to Architecture That Engages'. This is how he describes it: 'depicting what we call "loves": what we love, what inspires us, the range of which -- from Michelangelos to bungalows -- derives from our freedom and tolerance as artists and thinkers, freedom from the restrictions of ideology!'

'Mannerism -- rather than Expressionism / Mannerism -- rather than Minimalism / Or Modernism that is Mannerism / Iconography -- rather than Expressionism / Iconography -- rather than scenography / Iconographic Meaning -- rather than Abstract Expression / Architecture as Communication -- rather than as Space / For the Information Age rather than the Industrial Age'

It's an amazing distillation, accompanied by a selection of images of condiment bottles and the names of comic characters, that boils theory down to an even simpler residue: 'Viva Ketchup!' 'Viva Mr Bean!' These simplest of statements are a kind of post-theory. As though after all those years of writing and polemic, it's time to stop explaining.

Perhaps enough time has now passed since postmodern architecture's heyday for cool heads to prevail. Certainly, architecture has all but exhausted the formal extravagances of neo-Modernism: Deconstruction and Blobism, the tedious technology of high tech and the vacuous poetics of Minimalism. It seems a good bet that Venturi and Scott Brown's legacy could suggest alternative approaches to all of these, new ways of exploring the exciting complexities of architecture in the Information Age. And maybe even they will come to terms with Postmodernism. And I'll be able to enjoy all my cheap architecture books without any stigma attached.