Charles Jencks, the critic who helped bring postmodernism into existence, died this week. With populism on the rise, the pluralism of the movement is needed now more than ever, argues Owen Hopkins.

"Modern Architecture died in St. Louis, Missouri on July 15, 1972 at 3.32 p.m. (or thereabouts) when the infamous Pruitt-Igoe scheme, or rather several of its slab blocks, were given the final coup de grâce by dynamite."

Quotations don't get more famous than this – at least when it comes to books about architecture. Appearing early on in Charles Jencks' seminal work, The Language of Post-Modern Architecture, these lines even have their own mythology. Jencks subsequently admitted to having made up the precise time for the sake of rhetorical flourish and impact.

As a writer, critic and theorist, Jencks' great talent was to be able to put his finger on something – an event, a trend a movement – and to identify and articulate its significance. Postmodernism in architecture existed before Charles Jencks decided to call it that – yet, it was still a latent force, disparate and disconnected. In his work, postmodernism took centre stage and was polemicised as a set of values to which all architecture should subscribe, and which remain hugely important today.

Jencks achieved that rare thing as a critic: his polemic helped bring the movement into existence

The funny thing, though, was that when Jencks wrote the first edition of The Language of Post-modern Architecture in 1977, very little postmodern architecture yet existed. The chapter that actually deals with examples of the movement is very slim indeed, with few projects that we would now recognise as emblematic of the style. Jencks, therefore, achieved that rare thing as a critic: his polemic helped bring the movement into existence.

As he writes at the beginning of the book, Jencks' particular take on modernism's deficiencies were in terms of its failure of "communication", making clear the influence of semiotics and linguistic theory on his work. Modern architecture could work in some situations, he admitted, but 'certainly not mass housing, nor large-scale urban redevelopment'. For Jencks it was vital that modernism's 'claims to universality should be exposed as ideological'.

By the fifth edition in 1987, the triumph of postmodernism of the intervening decade allowed Jencks to describe a number of sub-categories of the movement and include a whole new chapter on 'The Synthesis: Post-Modern Classicism' with now familiar works by Charles Moore, Ricardo Bofill, Terry Farrell, Michael Graves et al.

However, as a critical practice postmodernism was already on the wane, as Jencks himself was only too keenly aware. By the late 1980s, it had become appropriated and transformed into a set of aesthetic signifiers frequently applied to commercial architecture.

Jencks, however, continued to plough the postmodernism furrow, its definition expanding to encompass architecture and architects who resisted the characterisation yet to his mind embraced its qualities. This made clear that despite his close association with postmodernism as the style of the 1980s, postmodernism for Jencks was always more a set of values than a particular aesthetic.

The Maggie's Centres are the archetypal postmodern hybrid

It was during these seemingly fallow years for postmodernism that these values found their most profound and lasting expression in the Maggie's Centres which he founded with his wife, Maggie Keswick, after she received a terminal cancer diagnosis in 1993.

The Maggie's Centres are the archetypal postmodern hybrid. They exist always in relation and proximity to a hospital and offer emotional support to those suffering from or affected by cancer, yet are not medicalised spaces. They are homely but open to everyone, public and private, places where, in Maggie's words, people should not 'lose the joy of living in the fear of dying'.

Jencks' unrivalled contacts ensured that a roster of global stars were lined up to create centres across the UK. All the architects were given exactly the same brief, which they were allowed to interpret into their own individual way. In this sense, Maggie's has operated as an kind of architectural experiment with the results counted in the number of people for whom they have provided support and sanctuary at the most desperate of moments.

The Maggie's Centres show the positive effect that architecture can have on people's lives without the resorting to the crude modernist idea that architecture should be an instrument of social progress, which Jencks had himself so decisively upturned. Aside from the practical assistance and support they offer, the Maggie's Centres show the deeper, more metaphysical benefits that architecture can bring, helping us understand our place not just in society or history, but in the cosmos.

Critics would no doubt see him as a kind of George Lucas figure: innovative early work, before getting hung up on single project that proves impossible to move beyond

This idea became the specific focus for Jencks' work as a landscape designer and in his own extraordinary house in Holland Park. Designed with Terry Farrell, the house reflects Jencks' belief that to build – to put a barrier between ourselves and the stars – is an elemental act, and that architecture must speak of the meaning of this profound undertaking. For all of his interest in codes and systems and classifications, this is what postmodernism meant for Jencks.

Critics of Jencks' would no doubt see him as a kind of George Lucas figure: innovative early work, before getting hung up on single project that proves impossible to move beyond. For Lucas this was Star Wars, for Jencks postmodernism. What's more, critics might add, these projects are responsible for much of what is wrong with our present situation. As Star Wars led to the all-consuming summer blockbuster, so postmodernism heralded the age of the iconic building.

Yet it is always unfair to blame something or someone for what came after, especially if their values stand in opposition to those of the followers or imitators. And if it's not stretching the analogy too far, like Star Wars, Jencks' ideas did not simply define one generation, they are constantly discovered anew by the generations that have followed.

As with the best writers and theorists, Jencks' work rewards repeated reading. This is all the more important when we consider the parallels between our own era and the two moments that Jencks was most fascinated by: the emergence of modernism in the 1920s and 1930s and of postmodernism in the 1970s and 1980s.

To resist the monomaniacal we must continue to embrace individuality, contingency and pluralism

Looking back, it becomes abundantly clear that our present situation of political and economic flux is seeing the 'grand narrative', which postmodernism had so decisively discredited, return with a vengeance, whether in narratives of nationalism and nativism, or of populism of both the right and left.

Thinking about how we might begin to articulate an architecture of resistance to these forces, we might turn turn to Jencks' book Adhocism, co-authored with Nathan Silver. 'Today', they wrote in 1973, 'we are immersed in forces and ideas that hinder the fulfilment of human purposes', in those days it was big corporations and modernism, comparatively benign to those we face today.

'But a new mode of direct action is emerging', they continued, 'the rebirth of a democratic mode and style, where everyone can create his personal environment out of impersonal subsystems … by combining ad hoc parts, the individual creates, sustains and transcends himself'.

These words remain as vital today as they were then. To resist the monomaniacal we must continue to embrace individuality, contingency and pluralism which, for Jencks, were at the heart of postmodernism.

Talking to Jencks was always an amazing ride: one minute we'd be discussing Soane's manipulation of space, the next it would be fractals and digital design. Interviewing him for the exhibition on postmodernism I curated at Sir John Soane's Museum last year, he described in typically irreverent fashion the impending 'great die-off' that would soon take place as a generation of starchitects now in the eighth or ninth decades began to step off the stage in quick succession.

It is deeply sad that Jencks was one of the first to go. His combination of provocation, generosity and an ever-enquiring spirit has never been more important.