I meet Julian Spalding in the Ashmolean cafe, on a sunny Friday morning. He was in the Union the night before, debating about Art. “It’s a strange place,” he says. “Straight out of the 1840s.”

Spalding is a writer and art critic, and a former curator. With tortoise-shell glasses and an open-neck blue shirt, he speaks quickly and clearly. It’s soon obvious from Spalding’s references to meetings with David Hockney or Anthony Blunt that he’s been on the art scene for a very long time.

In 1989, he was appointed as Director of Glasgow Museums. There were protests on the streets at his appointment – he was the first Englishman ever to be appointed. Spalding persisted and proved his critics wrong. Spalding established the Glasgow Gallery of Modern Art in 1996 before leaving the city in 1999, the same year he won the Lord Provost’s Prize for Services to the Visual Arts.

He then went to the National Museum of Denmark for a year. I mention the ‘Trundholm Sun Chariot’, a Nordic Bronze Age artefact, and Spalding leans forward, his eyes lighting up. “It’s amazing, isn’t it?” “Denmark is mostly bogland, and people used to sacrifice people and things into the bog, which were preserved well.” It’s a reminder that art isn’t just western paintings of flowers and the Virgin Mary.

Since 2001, Spalding has focused on writing about art and history, as well as travelling: “I saw all the sites around the world I’d wanted to see but never had” he says. “It struck me that there was a history of seeing. I realised that realisation and the way we see things had a history.”

In 2015, Spalding published the book Realisation: From Seeing to Understanding, which argued that art emerged from the ways our ancestors tried to understand the world. Spalding argued that the pyramids, with their tremendous physical weight, were an attempt to establish permanence, and to hold down the flat earth against the skies which revolve around their polar axis. It’s a truly fascinating idea.

We go on to to discuss the Parthenon, with the ring of mountains which surrounds it and it’s view to the sea: “The sun would shine in through the main door and illuminate the statue of Athena,” he says, “which is similar to Newgrange, in Ireland and Jain Temples in Southern India.”

But Spalding is perhaps best known for his withering attacks on contemporary, conceptual art. “When conceptual art first appeared, I started to say, ‘what is this? It isn’t very interesting.’” Ever since Damien Hirst first came onto the British art scene, Spalding’s been arguing that the conceptual pieces people like Hirst make are fundamentally valueless. “It’s not creative visually.” he said, and in a 2012 article for The Independent, he wrote “Damien Hirst’s ‘works’ are only of value if they’re works of art. They’re not.”

In 2012, the Tate Modern ran an exhibition of Damien Hirst’s works, starting with ‘The Physical Impossibility of Death in the Mind of Someone Living’, the famous formaldehyde shark, and going right through to Hirst’s later spot paintings, which Spalding dismisses as “wallpaper”. Spalding tried to publish a book about Hirst: 12,000 words, entitled Con Art – Why you ought to sell your Damien Hirsts while you can. His publisher rejected it. Spalding published the book online. It attracted an enormous amount of media attention, and Spalding was interviewed by news sources from across Britain and Europe, including the BBC. But the Tate banned him from the exhibition, and he was left to talk to the cameras outside. “To treat me like that is just ridiculous” he says. “I was a major figure – a curator and an art writer. I wasn’t nobody.” Spalding challenged Nicholas Serota, the Tate’s director at the time, to debate the issue publicly. Serota said no. “Conceptual art is a bubble”, he says. It’s hard to disagree when one Damien Hirst show, Beautiful inside my head forever, sold for £111 million at auction.

Spalding is certainly isolated in making the argument against conceptual art, but he isn’t alone. The art critic Robert Hughes said in 2005 that ‘The Physical Impossibility of Death in the Mind of Someone Living’ was a “cultural obscenity”. So why do Hirst’s works keep popping up in serious, high-brow galleries?

Dealers, Spalding says. For the art market, the museum is the gold standard, and dealers tell potential buyers that if Hirst works are good enough for museums, they’re good enough for you. “Galleries are funded by dealers. The Turner Prize is decided by dealers,” Spalding says. “Curators are losing their independence.” Combined with the corporatism of the influential Saatchi brothers – a pair of advertising moguls who funded Hirst at the beginning of his career – it isn’t hard to argue that money has corrupted the art world.

When one Da Vinci, the ‘Salvator Mundi’, sells to a Saudi-Arabian prince at auction for $400m, it’s hard not to wonder whether any single object is worth that much. For Spalding, art’s been commodified: “if you can get a Da Vinci, you’re guaranteed investment”, he says. During his time as a museum curator in the Thatcher years he’d ask for funds, only to be told that “if you want more money, just sell what you’ve got in store.” For Spalding, art work in museums is publicly owned; it loses all monetary value it might have had when it can be seen for free.

Thatcher’s message to curators commodified public art by implying it could and should be bought and sold. $400 million Da Vincis commodify art in a similar way. It’s often argued that the process of artistic commodification started with Duchamp’s ‘Fountain’. His urinal was exhibited in the Society for Independent Artists, supposedly to mock the art world by showing that they accept anything. If he said it was art, it was. That was the intention, at least.

But Spalding tells me that it was misattributed. The world of modern, conceptual art, he tells me, was built on a lie: “It all comes from Duchamp – the idea that anything can be an artwork if you say it is. But Duchamp didn’t do the urinal.” The urinal, Spalding says, was made by Elsa von Freytag- Loringhoven, a German dadaist and poet, and it was intended as a work of sculpture protesting America’s declaration of war on her homeland.

“She regarded America as a gentleman’s club, so she was telling America not to piss on her homeland. ‘R Mutt’ scrawled onto the mass-produced porcelain is both a pun on ‘Mutter’, the German word for mother, and the English word ‘Mutt’ – she was punning in German and English”, Spalding explains. He’s working off research done by Dr Glyn Thompson, an art historian working at the University of Leeds, who found, as definitive evidence, a letter in which Duchamp – who “appropriated it very early but never claimed it was his” – said “one of my female friends under a masculine pseudonym, Richard Mutt, sent in a porcelain urinal as a sculpture.” The evidence seems definitive.

“Modern art had a founding mother, not a founding father”, Spalding says, and it’s convincing. The idea that the urinal was a work of thoughtful and serious sculpture, not a middle finger at our conceptions of artistic composition changes the history of Modern Art.

Spalding promoted work in his galleries that was popular (Beryl Cook and LS Lowry, for example), and what frustrates him most about conceptual work is that millions of pounds of taxpayer money goes towards art that isn’t. For Spalding, art should be something which anyone and everyone can enjoy. So I ask him what he thinks the most accessible art museum in Britain is. He isn’t sure. “You need to see a few things, to look at what you like. And then go back”.