It had to happen. Postmodernism – the style of pink-painted pediments, marbleised MDF and leopard-skin plastic laminate, of the Chippendale skyscraper, the designer teapot and the acanthus-leaved Homebase, which seemed to give form to the consuming excess of the Reagan-Thatcher years and which the architecture and design world then dumped as summarily as a herpes-ridden lover – is back.
For some years, interesting architects have been playing with postmodernist themes. Now the V&A is honouring it with an exhibition which promises to make it look fun and important. It's only a matter of time before the former TV-am headquarters, famous for the giant eggcups on its skyline, and those of MI6, whose robotic forms a peevish critic once compared to Arnold Schwarzenegger, become listed buildings.
According to Charles Jencks, the man who applied the term "postmodernism" (or Post-Modernism, as he likes to write it) to architecture, it never went away, and he has published a book, The Story of Post-Modernism, to prove it. As evidence he cites decorative icons such as the Olympic stadium in Beijing, the Gherkin in London, and architects such as Edouard François, who has covered buildings with plants and stacks of large flowerpots. Terry Farrell, author of the TV-am and MI6 buildings, says: "Most of us are postmodernists now. We will never go back."
It all depends what you mean by postmodernism. By one definition it is a short-lived style of architecture and design, such as art deco, which flourished in the 1970s and 80s. It favoured ornament, ironic wit and bright colours. It was pop and classical at once. It revelled in being artificial and theatrical, with columns or arches supporting nothing, pumped-up cornices and weighty-looking rustication that sounded hollow when you tapped it. You could see it was a stage set, and that was the point. It set out to be everything that modernist design, which had aimed for undecorated honesty in form and structure, was not.
Alternatively, postmodernism is an attitude where surface is substance, which delights in its own hollowness. Frequent costume changes are the art of life. Its twin deities are the odd couple of the musician Madonna and the architect Philip Johnson, who in 1978 designed the AT&T building (now the Sony building) in New York – a pink granite tower with a Florentine arcade at its base and a broken pediment at its top that drew immediate comparison with a Chippendale bookcase. Johnson had previously been an enthusiastic supporter of modernism and had worked with Mies van der Rohe on the nearby Seagram building, an austere black glass box which was ostensibly AT&T's opposite. He would go through several more style changes before his death in 2005, aged 98.
For Michael Graves, whose municipal building in Portland, Oregon, was postmodernism's first major monument, it was a "critique of modernism's failure to deal with the human and the urban" and a rediscovery of the "humanistic discipline of architecture, where we are the primary subject, with scale and proportion – all of that above all else." It is about buildings people can understand and with it "how to make a window, a door, a threshold. A lot of buildings are just glass, you get your rocks off on how the glass is detailed – that's a pretty thin world."
Many of those most closely involved in postmodernism say it was countercultural and anti-corporate. In 1972, Denise Scott Brown, with her husband, Robert Venturi, wrote Learning From Las Vegas, a founding text of postmodernism which celebrated a city usually dismissed as vulgar and kitsch. She describes growing up in her native South Africa, where "the struggle was between what you saw and what you were told ought to be, between the diversity, the African folk pop-art, the beautiful landscape, and expats telling us we should behave like the English". Coming to London to study, she saw the same conflict between the "is" and the "ought to" in the lives of working-class people and the style of architecture that modernist architects tried to impose on them. "You should value what is, because people make it," she says, "not see it as bad because it is not your taste culture."
For her, as for Graves, buildings should communicate, which usually means they should be decorated in ways that mean something to their users. Just as important was their planning: they should be planned inside and out so that people are more likely to meet and interact. This, she says, is the main virtue of the Sainsbury Wing of the National Gallery, designed by her and Venturi and completed 20 years ago. "People think that all we've done is put neon on the cathedral, but it's much more than that."
For Jencks, postmodernism is about many things, especially plurality, complexity and the ability of buildings to symbolise almost anything, from the order of the cosmos to a hot dog. It was a reaction to "the triumph of nothingness", the modernist architecture which had, by the 1960s, become the official style of the establishment in both capitalist and socialist countries, a dogmatic, high church willing to compromise with business, which reached a new low when Walter Gropius, the high priest of modernist high-mindedness, designed the Playboy Club in London. The "death of modernism", according to Jencks, came in 1972, when the modernist Pruitt-Igoe housing complex in St Louis was demolished.
But then postmodernism suffered what Scott Brown calls "the corporate takeover that we call PoMo", when Philip Johnson, whom she calls "an evil man", unveiled his AT&T designs in 1978. Jencks describes the same moment as the time when postmodernism, if it did not die, "grew old", only six years after the death of modernism at Pruitt-Igoe. From there it was a slippery slope to a new Playboy moment in Disney's rolling out of resort hotels by leading postmodernists such as Michael Graves, and the adoption of the style as the standard wrapping for large office blocks of the 1980s boom.
With dismaying speed, the style of counterculture was consumed by the corporate. The V&A's show promises to reveal postmodernism as a thing of energy and pleasure, running across art, fashion and music as well as design and architecture. Yet by the mid-80s its invention had run dry and its wit had become lumpen. It became a useful trick for globalised finance, whereby large American practices could make a tower in China look like a pagoda or one in the Gulf look like a tent. It lived on its wit and, when it lost it, it was doomed.
Yet we are all, as Farrell and Jencks say, postmodernists now. The idea that a single style could dominate, as it did at the height of the modern movement, has gone for ever. The idea that buildings communicate, however clumsily, is contained in the remarkably imperishable idea of the "iconic" building. Ideas about city planning that owe something or other to Scott Brown's principles are contained in most large-scale masterplans for new developments. The results can be monstrous or beautiful. To have more of the latter, we need to rediscover the agility of postmodernism at its best, combined with Scott Brown's belief that design has something to do with improving people's lives.
Postmodernism: Style and Subversion is at the V&A, London SW7, 24 Sep-15 Jan
• This article was amended on 21 October 2011 to replace the term Formica (which is a registered trademark) with the words "plastic laminate".