Anthony Van Dyck, meet Tracey Emin. You've got more in common than you might think

Today, as I was walking past the Royal Academy in Piccadilly thinking about Austin Powers and Tracey Emin, I remembered what John Tusa's new idea was about how critics should carry on: we must not praise something simply because it succeeds on its own terms or because we know a lot about it. Or because we think, Ha ha, I get it! For what are we, if we are critics, if not critical? Plus, how can anyone understand what we're saying if we don't call a spade a spade but instead take our hats off to relativism and show our bottoms to excellence? Or worse, hide behind a mask of irony? In an age of uncertainty, how about some certainty!

I felt I was on the right path, like Christian in The Pilgrim's Progress. Of course, I had many rivers to cross, like Jimmy Cliff in The Harder They Come. But I would get to the Promised Land in the end, like Charlton Heston. I decided to try the new method out immediately on Van Dyck (who would have been an appalling papist heretic in John Bunyan's eyes), whose 400th-anniversary exhibition opens at the RA next month. He's so art-historical: how do we get a handle on him?

Van Dyck was foppish, small, thin, often ill, and died in 1641, at the age of only 42. He painted flattering, unbelievable portraits of royalty and aristocrats, and some religious and mythological scenes. He was a child prodigy, and was befriended by Rubens at an early age and taught by him. He often stole compositions from Rubens and turned them around, and then re-did them using his own painterly technique or signature style. This might seem a long way from what we value about the old masters - their boundless imagination and originality - but in fact it was normal. Although he was a noble poshie himself and could identify with the aspirations and self-image of his noble sitters, he had a straightforward attitude to being an artist. It was a job, and he did it for pay.

If someone liked a portrait he'd done and wanted him to do it again but a bit differently, maybe with a different face painted in, he would. It was like someone today asking for a job of interior decorating to be carried out. Many of his portraits look like faces poked through fairground screens. Many of them weren't painted by him but by assistants. He accepted so many commissions, he couldn't see them all through by himself. He wasn't particularly good at hands.

On the other hand, he hardly did anything that doesn't have something shimmery and remarkable about it somewhere - the rendering of hair, a sheen, a highlight, some leaves. Often, his paintings seem like composites of different parts, and not like convincing organic wholes. But his portraits of King Charles I and Queen Henrietta Maria are wholly lovely. One from 1613 is staggering. It's not the colour so much - although the colour is beautiful - but the apparition of form, the luminosity and subtlety of the paint handling.

So that's the other main thing to remember about Van Dyck besides court portraiture - his painterliness. Subtlety with him is in the lightness of touch, the way the paint can seem to do everything from a sheen to flickering transparency to heavy darkness. You could say sheer virtuosic painterly touch is unquestionably good and transcends all other considerations. Even that it's the only thing we can really relate to about Van Dyck's art, since we don't care about kings, or about high learning and a lot of allusions to antiquity and a great classical past.

But in our age, painterliness is not a pleasure particularly valued by everyone, but only by a cultivated few. So its goodness is questionable after all. And in fact Van Dyck himself is a shimmery art-historical figure for us, fading in and out of the public consciousness, until now mostly out. He was a contemporary of Rembrandt, Rubens, Franz Hals, Velasquez, Poussin and Claude Lorraine. Van Dyck is the shallow one.

But he was a genius at shallowness, like Andy Warhol. They both do portraits and shallowness, and they both find ways to enrich the superficial so it seems almost to be deep. In Van Dyck's case it was through a kind of of supreme painterly finesse, his way of giving life to form.

His subtlety inspired succeeding generations of English painters from Gainsborough to Turner, including Joshua Reynolds and Thomas Lawrence and even Hogarth (who hung his own portrait of Van Dyck outside his shop). They thought he was the initiator in England of a great tradition, which he was, and they loved him.

And we love them. Or at least we love their subject-matter - English behaviour, manners, faces, the weather, the English landscape. But we don't love him. We hardly know who he is and if we are honest we must admit we often get him confused with Van Eyck, who painted white church interiors or Dutch Still Lifes (or something).

But it's not Van Eyck: it's Van Dyck, or Sir Anthony Vandyck as he became known following his Englishification. Born in Antwerp, he worked in various parts of Europe, but spent the last 10 years of his life employed by Charles I as the court painter. He got his knighthood from the king, as well as an annual stipend, plus a fee for every painting he did for the king, and a free house and studio in Blackfriars, with the lively barges going by and the 17th-century bargees calling out for passengers - Westward Ho! Here, I had that Sir Francis Bacon in the back of the barge the other day! Eastward Ho!

Hang on, though! I could virtually see John Tusa in Piccadilly Circus now, getting really angry! Only 500 yards up the shining path and already we're thinking shallowness is good, plagiarists can be geniuses and something unquestionable can be questioned. Sorry, John! I really want to get some enlightenment and I know you do too! How about a different tack?

As a contemporary-art enthusiast and apologist, what do I get from Van Dyck that I don't get from Tracey Emin? And vice versa? And for this lap I'll have to be straight and strong as well as frank. In fact, I'll be like St George, with a heart of oak, like Van Dyck's painting of Charles I on the edge of a great forest, under a mighty oak, which was finished in 1636 and known to its admiring audience of then as "The Greate Peece".

It was in fact a time of great peace, but not so much of great English woodlands and Robin Hood (even though it was the period when the Robin Hood myth first started up), because the king was selling off great chunks of woodlands to unscrupulous nobles. He needed the money to pay for works of art brought in from abroad. And for elaborate, costly court masques, and performances which were precious and frozen and cut off from the reality of life.

Instead of life, they expressed the dream reality of the court, which was a big illusion. It said that the king and queen were the incarnation of the new values of England. These were connected to the values of Imperial Rome now, following the ending of barbarism with the rise of the Stuart dynasty. England was the centre of civilisation, and anybody civilised would want to come and live here instead of staying abroad. And the lovely big forests of England were a symbol of this new paradise on earth.

The king auctioned off the whole of the Forest of Dean one day, to keep the illusion going. It was bought by a duke who promptly chopped down a third of it. No wonder there was a Civil War! And it was lucky for Van Dyck he died of natural causes a year before it started.

Anyway, Van Dyck offers us on the one hand amazing accomplishment and visual richness, and on the other a lot of images of the doomed court. It is possible to like both of these. It was an age where the arts and political ideology were joined together in a fascinating way, where there was an infinity of subtle tiny significances and an infinity of pleasures. And it's clear that our leader today could learn something from that.

Authenticity, sincerity, the depths - we don't get these from Van Dyck, because he never believed it was his job to offer them. It wasn't Rembrandt's job either but he did it anyway, and died a pauper. Whereas Van Dyck died rich. And now Tracey Emin's rich, and she's up for the Turner Prize. Where does her authenticity lie?

Running through everything she does is a confessional rhetoric so seemingly puerile we can't believe this really is the centre of what she's about. And that's right, it isn't. She's about nerve. And neck. And these are good. We stand amazed at her confidence. We find it quite amazingly authentic. We wonder if she secretly believes what she does is juvenile but it's more amusing and it makes life seem richer to believe she doesn't. And that way it goes on being an open question for us too. Hey! How long can she keep it up?

Well that's enough comparing a four centuries-old art of exquisite painterly refinement which has its roots in the even more ancient art of the Venetian masters Titian and Giorgione with a totally contemporary art of vivid sensations and excitements which exists in a world of nutty kitsch films and fantastic ads. Like the new one for the Renault Clio 16v which I really like, where there's just a woman's laughing expectant eyes and a caption in little letters that reads: Size matters.

How about asking what there is in Van Dyck's art that resonates with the here and now? Our time is so different. We simply don't have a living tradition of painted portraits expressing high ideals. We have a tradition of photo portraits expressing glamour, with Cecil Beaton and David Bailey as its stars. We have photo-realist paintings by Chuck Close which only have an ironic relationship to portraiture and to painting. And because we don't have a set-up where a Van Dyck would be possible or necessary, where a fictionalised royalty could be projected in dream images, and instead we see our own real royals all the time - we feel they are quite spectacularly daft and ugly. Whereas they probably aren't any more so than the Stuarts were or any of the other dynasties.

But still, Van Dyck fits in for us. It's because of his shallowness, not in spite of it. Shallowness is what we're interested in and fascinated by - its unexpected intensities and pleasures. It's what our own big cultural adventure, or exploration, in our own time of great peace, is all about.

'Van Dyck 1599-1641': Royal Academy, London W1 (0171 300 8000), 11 September to 10 December