Thomas Sutcliffe: Is this money for art's sake?

The Australian art critic Robert Hughes was in characteristically pugnacious form the other day, interviewed on Radio 4's Front Row for a curtain-raiser to the London Art Fair. "Obscenity" was the word he used to describe the prices now commanded in the salesrooms of London and New York for artists - or rather artworks - in the highest earning bracket. And Hughes - who has a long record of thoughtful attention to the relationship between monetary and intellectual value - repeated a repudiation he's made before. "Art criticism has nothing to do with the question of whether some Jasper Johns sells for $135m dollars or not," he said. "What things sell for is not my business. What I'm interested in is what they mean and what they are worth aesthetically and intellectually." This is, of course, a well established opposition, most tautly represented by that Wildean description of the cynic as someone who "knows the price of everything and the value of nothing".

The following morning, by one of those minor coincidences of the cultural life, this polarity popped up again on the Today programme, during a report on the increase in significant finds by amateur metal detectors (or at least the increase in reported finds, since it became a legal obligation). In contrast to the Culture Minister David Lammy, who earlier this week described amateur metal detectors as "unsung heroes of the UK heritage", Frank Baldwin of the Battlefields Trust was arguing that they could be as great a threat to our historical heritage as developers who concrete over the site of a battle. And naturally he, too, contrasted a market price with a less tangible valuation: "The financial incentive to go out and find objects which might make you a few thousand... well, all right, that's a few pounds but actually it's destroying something that's priceless, which is the story of our past."

Well, one knows what he was trying to say - but surely the problem is precisely that the story of our past isn't priceless at all but has a market value. Indeed, the 1996 Treasure Act acknowledged that fact by offering conscientious detectors half of the sale proceeds of officially declared treasure. I take it that what Mr Baldwin meant was that the intellectual value of archaeological finds far exceeds their market value and yet can effectively be overridden by a price tag. And, though he didn't say it explicitly, there was the suggestion that these two value systems are inimical and unconnected. If you're a money-grubbing cynic you'll settle for one - if you're greedy for beauty you'll give the other priority.

The truth, though, is that intellectual value and market worth can't simply be separated in this way. Luckily, very few treasure finds are worth as little as the scrap value of the metal they're composed of - otherwise archeologists would have a truly horrendous problem. And the difference between the material value of the object and its actual market price can only really be explained by the penumbra of historic appeal it carries with it. True, there's a bit of collectors' frenzy in the calculation, too - but even that demand rests on an entirely intellectual notion - that this bit of corroded bronze, stamped with the image of a long-dead king, has a value not shared by the trouser button that was unearthed alongside it.

Robert Hughes's confidence that prices in the modern art market have nothing to do with him strikes me as similarly wishful. He may not consciously care about such matters at all - and indeed he's shown considerable resilience as a critic in ignoring the changing tides of fashion. But the truth is that art criticism has everything to do with the price of Jasper Johns. There are artists who make a healthy living in the teeth of almost universal critical disparagement - but Jack Vettriano is never going to break any salesroom record except those set by his own pictures. And while the higher reaches of the contemporary art market may have achieved a tulip fever critical mass - in which pictures are bought because it is virtually certain that they will increase in value - it's worth remembering that tulip fever was built on a foundation of aesthetic value.

I'd be willing to lay a large sum of money that if the cultural consensus on Warhol changed from admiration to indifference, salesroom prices would soon follow the downward curve. What people buy when they buy high art or antiquities, after all, is esteem, and it is critics and historians who provide the provenance for that intangible good. The more that they insist on the incompatibility of intellectual value and cash, the more they bolster the price. You only need one word to cover both aesthetic admiration and monetary growth: it's "appreciation".