When Ernesto Laclau passed away last April aged 78, few would have guessed that this Argentinian-born, Oxford-educated post-Marxist would become the key intellectual figure behind a political process that exploded into life a mere six weeks later, when Spanish leftist party Podemos won five seats and 1.2m votes in last May’s European elections.

Throughout his academic career, most of which he spent as professor of political theory at the University of Essex, Laclau developed a vocabulary beyond classical Marxist thought, replacing the traditional analysis of class struggle with a concept of “radical democracy” that stretched beyond the narrow confines of the ballot box (or the trade union). Most importantly for Syriza, Podemos and its excitable sympathisers outside Greece and Spain, he sought to rescue “populism” from its many detractors.

Ernesto Laclau. Photograph: Chantal Mouffe

Íñigo Errejón, one of Podemos’s key strategists, completed his 2011 doctorate on recent Bolivian populism, taking substantial inspiration from Laclau and his wife and collaborator Chantal Mouffe, as he explains in this obituary. To read Errejón on Laclau is to take an exhilarating short-cut to understanding the intellectual forces that are shaping Europe’s future. Syriza’s victory in Greece, for one, has been directly driven by the ideas of Laclau and an Essex cohort that includes among its alumni a Syriza MP, the governor of Athens, and Yanis Varoufakis. Syriza built its political coalition in exactly the way Laclau prescribed in his key 2005 book On Populist Reason – as Essex professor David Howarth puts it, “binding together different demands by focusing on their opposition to a common enemy”.

On the Mediterranean side of austerity Europe, the common enemy is not hard to discern. During Spain’s massive indignados protests and encampments of summer 2011, one of the principal slogans was the quintessentially populist “We are neither right nor left, we are coming from the bottom and going for the top”. It is, in Laclau’s terms, “the formation of an internal antagonistic frontier” like this, between a broadly defined sense of “the people” and a ruling class unwilling to yield to their demands, that readies the ground for a populist movement like Podemos.

You can see the same political and social realities, the same fertile ground for a mass populist movement, and the same possibility of “radical democracy” in the stunningly successful Spanish housing activist group PAH. A 2013 poll for El País found 89% support for PAH’s campaign of direct action, eviction-blocking and escraches (demos outside politicians’ houses). Amazingly, the approval figure remained almost as high among voters of the governing rightwing Partido Popular, at 87%.

With more than 500,000 evictions since 2007, and Spanish prime minister Mariano Rajoy enacting Troika-mandated swingeing cuts to public services, there have been times when Spain’s social services have contacted one of PAH’s 150 local branches for help. When a radical activist movement has become so successful that it is called upon to do the work of the state, not just by vulnerable citizens but by the state itself, the political conjuncture is striking in its uniqueness. Podemos is drawing directly on Laclau’s work to make the most of this opportunity, rejecting the old Spanish left of the PCE (Communists), smashing the discredited austerity-lite of the PSOE (Socialists) in the polls, and channeling a rehabilitated notion of leftist populism.

Laclau’s goal was to invert the analysis on populism – overturning the received wisdom that, explicitly or implicitly, always uses the term pejoratively. Usually, describing a person or a movement as populist implies that they appeal to basest instincts, hitting the lowest common denominators like a hammer on windchimes, sacrificing intellectual acuity in the name of short-term success.

Why, Laclau asked, should this necessarily be so? What if vagueness, simplification and imprecision were good, necessary qualities in a political movement? He writes: “Is not the ‘vagueness’ of populist discourses the consequence of social reality itself being, in some situations, vague and undetermined?” It is important, Laclau goes on, to “explore the performative dimensions” of populism. What is the process of simplification and emptying in aid of? What is “the social rationality they express”?

In the case of Podemos, repeatedly attacking la casta (the elites) may seem simple or trite on paper, as some have argued, but expressing your disavowal in the context of Spain’s domination by a corrupt, unreformable “regime of 78” (the year of the post-Franco constitution) which is in thrall to the troika and their friends in the bailed-out banks, as well as 40 years of Francoist patriarchy before that, becomes potentially transcendent.

Laclau also encouraged the likes of Podemos to think about who is served by anti-populism. The dismissal and denigration of populism has been “part of the discursive construction of a certain normality, of an ascetic political universe from which its dangerous logics had to be excluded”. It is here that Laclau’s words illuminate the present crisis: this universe, this constructed normality, is tragically familiar. It is one in which the centre polices the boundaries of political thought; and it is a universe in which Ed Miliband can be called “red” while promising to enforce neoliberal austerity policies. It is also a universe in which prominent leaders of the nominal left, from the Parliamentary Labour Party to Trotskyites, exhibit a pathological lack of faith in large swathes of the population.

And this is the nub: populism is seen as dangerous because democracy is dangerous. “Rationality belongs to the individual,” Laclau writes, characterising the anti-populist thesis, and when the individual takes part in a crowd or a mass movement they are subject to the most criminal or beastly elements of that group and undergo a “biological retrogression” to a less enlightened state of being.

Elite contempt for the masses has been fairly easy to identify in Spain’s recent history – a land of patriarchs, landowners, priests and, above all, Franco, the nation-state’s chiding father. The indignados were not the first to protest in their millions in Spain. Podemos leader Pablo Iglesias says his earliest political memory is the anti-Nato demonstrations of the 1980s. There was also Iraq and the mass trade union demos and strikes of the 1970s and 80s. The Laclauian fault-lines between a mass of “the people” and “the regime of 78”, already existed with a certain degree of solidity before 2008 – but it has taken the remarkable series of events since the start of the crisis to harden that “internal frontier”.

Spanish politician Pablo Iglesias has noted that the conversation in the squares in 2011, and subsequently on left TV chatshows like La Tuerka, had become much more important than the one going on in parliament. The developments in Spain since 2008 amount to what Raymond Williams called a new “structure of feeling”, a shift in the lived experience of ordinary people, a new chain of demands distributed through more public, more truly democratic channels. What changed was something, in Iglesias’s words, “that functions in the magma and suddenly makes many people in this country see a guy with a ponytail on television and listen to him”.