Farshid Moussavi: "We are in a world where ideas migrate" Architecture today operates in a promiscuous haze. It is so easy to see, swap, trade and imitate ideas that it's hard to see what happened first where, what is original, authentic or new. Just as styles in fashion migrate rapidly from the catwalk to Primark so it is in architecture. There are the big names, the people recognised as originators, and what might be called hack practices, who feed off their inventions; but as staff and inventions migrate between the two it can get hard to see the difference between an off-day production by the former and an above-average performance by the latter. There are also plenty who are neither big nor hack, and work in the wide open spaces between the two. It is an environment in which Farshid Moussavi is happy to operate. "I am excited by being an architect now," she says. We are in a world where ideas are shared and migrate. There is no going back, so let's go beyond. Let's look at what really are the differences between, for example, two housing projects that both have curved balconies. Architecture makes a difference. Let's discuss what difference it makes. To this end Moussavi is bringing out a book called The Function of Style, the third in a series - the previous two were about ornament and form - which in an almost 19th-century way attempts to redefine the basics of architecture. They don't, however, describe their subjects in conventional ways. If you think of style as being about external appearance, as something that can be added and taken away, Moussavi does not. Rather she presents project after project, over 600 pages, in an analytical way - it should be said this is a book for professionals and students. Things like materials, location and authorship are underplayed in favour of organisational ideas, which are where, by implication, style lies. The works shown are by stars, hacks and honest practitioners, and run from Dunedin, New Zealand to Anchorage, Alaska by way of Singapore, Riyadh and Ipswich. Some of Moussavi's own works are included. The design for Moussavi's Les Jardin de la Lironde residential complex in Montpellier, Paris. Photograph: Farshid Moussavi Architecture Most of the works are from the past 20 years when, she says, "so much production has happened - what did we learn from them?" The same period is also the span of Moussavi's career. In 1995 she and her now ex-husband and ex-business partner Alejandro Zaera-Polo beat 795 other entrants to win the competition to design the £150m international port terminal in Yokohama, a spectacular breakthrough for a pair then aged around 30. If the function sounds run-of-the-mill, both the city and the architects wanted it to be anything but. The building, a long pier whose undulating wooden decks fused the transport facility with a public open space, a sort of artificial park for the citizens of the city, was one of the projects of the decade. Moussavi and Zaera-Polo called themselves Foreign Office Architects, in reference to the fact that she was Iranian-born, he Spanish, and that they were working in a London office on a project in Japan. They were the epitome of a modern globalised practice. Since they split in 2011, Farshid Moussavi has had to re-establish her practice in her own name, and now has an intriguing range of projects - a tower in the City of London, an apartment block next to the Grande Arche in La Défense, Paris, the expansion of a famous department store also in Paris and a housing tower in Montpellier. In 2012 she completed the Museum of Contemporary Art in Cleveland, Ohio, which had started as an FOA project. In September Victoria Beckham's flagship store opened in Mayfair to Moussavi's designs. Moussavi at the opening of the Museum of Contemporary Art Cleveland, Ohio in 2012. Photograph: Duane Prokop/Getty Images The store, says Moussavi, demonstrates her belief that "the more we have the internet, the more physical space becomes powerful." She invites me to compare dating in the virtual and the real worlds: the latter "is more social, unpredictable." In the case of the store, Beckham sells a lot online, so the place functions as "a gallery." It is a generous series of spaces on three levels, dominated by grand staircases, diagonal geometry and mirrored ceilings, walls and counters. The products are almost incidental - a light scattering of bags greets you on a wall whose shelves are retractable, so that the space can be used for events. Later you find clothes hanging on a gold-coloured saw-tooth rack - which stops the hangers sliding irritatingly together - or on chains hanging from the ceiling. The latter, apart from their whisper of bondage, illustrate what Moussavi calls "affect," a favourite word of hers. Architecture, she says, "produces platforms for the way people engage with uses of buildings," in which way it is about "the politics of everyday life. Not in a big sense, because architects are not politicians, but in the way it influences the way people interact" - which interaction is with both other people and the physical environment. I am interested in architecture being a critical practice that has to do with life. The chains make you think a little about the act of putting a garment off or on its hanger, and make a small connection between you and the space as you do so. The reflections, the stairs, the hard and shiny surfaces also in different ways make you conscious of your presence in the space. So does the front door, a panel of concrete which, in the style of Rachel Whiteread, bears the negative of a sash window higher up the building's historic facade. Set within a wall of frameless glass, it is palpably heavy and a touch forbidding, but slides weightlessly away as you approach. Moussavi likes fashion: "I remember all the shops in London going back to the 1970s." She says she enjoyed working with Beckham who, for the record, is "a great designer." Victoria and her husband "are very likable people... If she sees something she likes she says so immediately. If she doesn't she stays silent. That's a great quality. Perhaps I should learn from it. At the same time Moussavi likes heavy things, infrastructure and the biggish buildings she is also designing. Moussavi's Museum of Contemporary Art Cleveland, Ohio. Photograph: Dean Kaufman On her larger projects she manipulates decisions of organisation or construction to achieve the affect which in the store is done with small things. Her housing near La Défense is almost a straightforward, stratified block, but she skews the floors from time to time such that they angle towards the view and provide some shade to the floor below. Her Montpellier housing tower is a stack of sinuous shapes that looks superficially like the sort of stuff that spews out of architects" computers the world over, except that it is driven by the wish to place balconies so that there is the minimum of overlooking between them. Her office block in Fenchurch Street is mainly about its severe-but-sensuous wrap of dark glass, in concave vertical strips like the fluting of a column. No one project looks much like another, in keeping with her belief that, now, a repetitive artistic signature makes little sense. She likes both thinking and building - "I wouldn't enjoy just having ideas." If she talks of affect and a kind of sensuality, there is also toughness in her work. It is these combinations - of intellect, construction and life - that make her approach appealing. The Beckham store begins to show what they might mean in practice. What will be more intriguing will be to see them applied at the scale of cities. The Function of Style by Farshid Moussavi is published by Actar D in January