The Venice Biennale manifesto of Grafton Architects is proof that vapid commentary can diminish great architecture, says Owen Hatherley.

"Freespace focuses on architecture's ability to provide free and additional spatial gifts to those who use it and on its ability to address the unspoken wishes of strangers," reads the manifesto of Venice Architecture Biennale curators Yvonne Farrell and Shelley McNamara, of Grafton Architects.

It "provides the opportunity to emphasise nature's free gifts of light – sunlight and moonlight, air, gravity, materials – and natural and man-made resources", they claim.

In Freespace, everybody will be free to wear sunscreen.

The pair were quickly criticised, not just for being so vapid, but for how oddly the manifesto sat with the confidence and power of Grafton's work. As Tom Wilkinson wrote in the Architectural Review: "The dismaying contrast between this text... and Grafton's meaty, assertive buildings could hardly be more striking or more strange."

It would seem that designing a building and writing about, or even thinking about, that building are very different processes of thought and action. Extreme talent in one doesn't necessarily transfer to the other – something art teachers have always known, even if it still surprises people that someone who can design an astonishing university would be unlikely to pass its theory exam.

The manifesto was criticised for how oddly it sat with the confidence of Grafton's work

Ironically, in one part of the biennale the V&A is exhibiting a fragment of Robin Hood Gardens, a London housing estate built in 1972, but which is now undergoing demolition. The largest work by Alison and Peter Smithson, it represented, perhaps more than any other, this problem from the other side. As architectural historian Mark Crinson points out in his new book Alison and Peter Smithson: "You would have to go back to the great gothic revivalists to find British architects with a similar sense of the potency and necessity of the written word" to these two.

The Smithsons' prolific manifestos, reviews and strange, uncategorisable book-objects (from one on the Euston Arch, to one by Alison on driving around in her car) have what Crinson identifies as a common thread. See Alison's review of Le Corbusier's La Tourette monastery, in which she notices every small detail, to the point where the detritus of everyday life dominates the grand architectural gesture.

Similarly, their exhibitions – Parallel of Life and Art, This Is Tomorrow, House of the Future – were packed with ideas about technology, society and science. Imagine the scorn these two silver jumpsuit-wearing theory-hipsters would have faced for a manifesto like Freespace. Crinson's book is the first to discuss them as architects of actual buildings, a vocation where their talents were always a little more questionable.

Sometimes the Smithsons, as architects of real buildings, would simply give grandiose and erudite names to totally ordinary details. The trellises on the Garden Building at St Hilda's College, Oxford, formed a "yashmak". The mundane cornices on the dour University of Bath buildings were "Moghul chhajjas".

But what Crinson can't say is that their ideas were just fine, for the most part. They were just better executed by others who knew when to stop thinking.

The book exhibits Farrell and McNamara's flair as designers and banality as writers

It is not to endorse the wasteful and socially disastrous demolition of Robin Hood Gardens to admit that the basic design, though admirable, was pointlessly complicated by elements that showed the terrible dangers of overthinking, from a communal "mound" so steep hardly anyone would use it to aggressive noise-abatement walls that made the place feel like a fortress.

Comparing it to the effortless logic and grandeur of Park Hill in Sheffield, by their students Jack Lynn and Ivor Smith, would be cruel. But without being able to draw upon the Smithsons' writings, and unbuilt manifesto-projects like Golden Lane and Sheffield University, Park Hill would have been a far lesser project.

Crinson's book makes a striking contrast with Robert McCarter's just-published Grafton Architects, the first monograph on the Irish duo. It is full of examples of Farrell and McNamara's flair as designers and banality as writers. Like the Smithsons, they are obviously interested in questions of urban form, landscape and montage, and the points where the mundane "human scale" details of a city meet the "inhuman" scale of heavy, powerful architecture.

But as the volume's photographs show, Farrell and McNamara express this much better in their actual buildings – in Lima, Milan and Dublin – than in their "Little Book of Architectural Calm" rhetoric. Telling us, "philosophical anchors are things that for us remain true, things that have stood the test of time," is a long way away from the Smithsons' attempts to pull "rough poetry" from mass production and mass media. And this prose contrasts jarringly with the poetry of the images.

The buildings themselves are obviously products of intellect and imagination, rejecting received ideas. Bocconi University in Milan, for instance, is a harsh riposte to the banal, pretty-pretty approach to "context" and the assumed wisdom that brutalist approaches to form and urbanism have "failed", meaning all we can do is offer politely clad infill.

Some of the more recent Grafton buildings display a real shock and vehemence, which is exceptionally bracing in the world of New London Vernacular and the like. But when it comes to explaining what they do, Grafton falls back on the platitudes of much duller architects. And though McCarter has a stab at explaining them through the ideas of "topographic section" and "carved space", it's pretty approximate.

When it comes to explaining what they do, Grafton falls back on platitudes

So are writing and building just fundamentally different forms of human expression? There have been designers who can excel at both buildings and books, permanent architecture and exhibitions, but it's becoming rarer and rarer. This might have something to do with the way philosophy and theory are approached in a facile way to embellish a degree project for a passing grade – a little dressing of Heidegger or Deleuze to impress your examiners.

This tends to discredit ideas, leading to the sort of insipid empiricism found in Freespace. Architecture is about light, space, people and nice things being nice.