Putting flesh on Poussin's bones Iain Gale finds Sir Denis Mahon, last of the great gentleman scholars, still pa ssionate in his defence of Poussin the sensualist

`Look at the painting closely and you can see the shaky hand of an old man at work. He preferred to paint landscapes in his late period because he cou ldn't cope with figures. Everything is askew. Nature is taking over'

They called it `l'annee Poussin'. In 1960, for the first time ever, art historians had the opportunity to see all of the major works of Nicolas Poussin in one place. They came together in the Louvre, in a show curated by Anthony Blunt, then acknow ledgedas the leading expert on the artist. It should have been the apogee of Blunt's career but, in the course of the exhibition, his authority received a severe blow from which it was never to recover. The challenger, in a famous article for the Burlin gton Magazine, was another art historian, the connoisseur of 17th-century Italian painting, Denis Mahon.

Now, 35 years on, as the Royal Academy prepares to unveil its own Poussin retrospective, Mahon is still frustrating the received wisdom of intellectual Poussinism. A small, genial, dapper man of 84, knighted, decorated and feted at home and abroad, Sir Denis Mahon is the epitome of the gentleman scholar. His conversation is peppered with French and Italian expressions in a way that suggests necessity rather than pretentiousness.

"It's discutibile," says Mahon of Poussin's oeuvre. Opinion remains divided on the authenticity and chronology of some 200 possible surviving works by the artist, making this exhibition potentially even more important than that of 1960. As Mahon says, "It's a unique opportunity. I never thought I'd survive to see these pictures together again."

In 1960 he wrote of the experience: "One is virtually compelled to take up a position as soon as one enters the exhibition ... I simply cannot bring myself to swallow the disparities which emerge, or the series of fundamental volte-faces." When the exhibition was taken down, he made sure he was present: "I was allowed to tell the staff at the Louvre, `Put this picture next to that one' and so on. I learnt a hell of a lot in a few days that would normally have taken years. Blunt had never seen the paintings together and so he made an awful hash of it. I plunged into a series of articles which said, `Oi! This is wrong and that's wrong.' " Blunt, according to his friend, the art critic Brian Sewell, was dreadfully hurt. It was, Sewell says: "a direct assault on another man's scholarship ... not in the language of discreet controversy".

According to Sewell, as he and Blunt had walked through the Louvre exhibition, the eminence of the Courtauld admitted his fallibility, repeating over and over: "I was wrong." The problem, Sewell says, lay in the fact that Blunt had arrived at his theory of Poussin's development using notes made many years previously, often before cleaning had entirely altered a painting's colour and mood. Indeed, as Mahon says, Blunt was denied access to some paintings, such as The Adoration of the Magi in Dresden, "forreasons we now know all about".

In his monograph on Poussin, republished this month, Blunt stated his aim as, "to revive and develop the conception of him as pictor philosophus ... In creating his paintings," he argues, "Poussin was inspired by a desire to give visible expression to

To illustrate his thesis, Mahon alights on one painting. the Landscape with Diogenes, now in the Louvre. According to Blunt this work dates from 1648 when Poussin turned to landscape as a genre with the series which includes Cardiff's Funeral of Phocion,Liverpool's Ashes of Phocion and the Louvre's Orpheus and Eurydice. This dating however, reiterated in the RA catalogue, poses problems for Mahon: "To say that the Diogenes was painted at the same time as the Phocions and the Orpheus is crackers. Look at it closely and you can see the shaky hand of an old man at work." Mahon believes that the picture belongs within the 1650s group including the Landscape with the Blind Orion in New York and the Hercules and Cacus in Moscow. His reaso ns are convincingly simple.

"Poussin preferred to paint landscapes in his late period because he had a shaky hand. He couldn't cope with figures. The Louvre's Diogenes is a wonderful example of that late style. Everything is askew. Nature is taking over. In the Phocion group the Stoic story gives birth to wonderful architectural constructions."

In Blunt's view, it is precisely this Stoicism which motivates Poussin. For Blunt, Poussin saw both Phocion and Diogenes as Stoic heroes, viewing Diogenes as "a sort of ne plus ultra of Stoic self-abnegation". But even in reproduction a basic difference is evident between the paysage heroique of the Phocion group and the paysage poetique of the Diogenes. Blunt, grouping the two together, chose to obey documentary sources rather than respect the evidence of his eye. He followed verbatim the testimony of Poussin's early biographer, Felibien, that a picture of Diogenes was painted in 1648. Mahon, however, concluded that the Diogenes mentioned by Felibien must be a different, unknown picture. Finally, in 1988, this was identified as being the Prado's ThreeMen in a Landscape, (whose central figure is, without doubt, Diogenes setting off for Athens) stylistically datable at 1648.

The consequent conclusion - that the Louvre picture dates from the 1650s - helps counter the argument that Poussin was an intellectually motivated artist capable of working in a number of diverse styles at the same time. It strengthens the impression that, from the 1640s, his work shows a steady progression towards those atmospheric qualities argued for by Mahon in his plea for Poussin as a painter, recently echoed by Neil MacGregor, the director of the National Gallery. MacGregor (ironically, a form erpupil of Blunt), published his support for Mahon in an essay included in the French catalogue for the RA show. Sadly, this is not included in the English catalogue whose entry for the Louvre Diogenes emphasises that "Mahon's view has not generally bee nfollowed".

If this second "annee Poussin" is to help with a definitive analysis of Poussin's oeuvre, part of the responsibility lies with the British public. "For 200 years," Mahon says, "the British have understood Poussin instinctively." Mahon believes that at the RA the pictures will at last speak for themselves. It seems only fair though, with Blunt's text and the French catalogue widely available, that Mahon's Poussiniana and its related texts should also be re-published. Ultimately, though, the pai ntings will have the last word. As Mahon says: "It's the man who worked on the canvas that matters. Poussin. One of the greatest painters who ever lived."

Royal Academy from 19 Jan.

`Poussin' by Anthony Blunt (Pallas Athene on 19 Jan, £19.95)