Frank Auerbach - in the thick of it

I could write like that if I had enough ink," Stravinsky said about Olivier Messiaen, (those densely scored compositions). Artists have had similar doubts about Frank Auerbach.

They could paint like that, if only they had enough paint! For really, what does all this heavy viscosity amount to? Isn't he laying it on a bit thick?

And already, just for saying that, I feel bad. I've made a joke, not even a joke really, but I've used a humorous tone in the vicinity of the art of Frank Auerbach, and I feel bad. I'm letting myself down. I ought to know better. I do know better. But it's the same every time, when I go to an Auerbach show, whether or not I actually make a joke. The work is very serious. And I myself (serious person that I am) don't feel quite serious enough.

Auerbach is the gold standard of artistic seriousness. (Anselm Kiefer? Don't make me laugh.) And I must admit it, I kind of rely on him. Whenever I feel that contemporary art is simply too frivolous or smart or crude, and then ask myself, "so what would seriousness be?", though I know he's too good for me, it's always Auerbach's work to which silently I appeal.

He's the great counterweight. He's there, keeping the side up. That's what seriousness is. He's the living definition. And the fact that he's there makes the other stuff seem all right too. The boys and girls can lark and gurney around all they like, so long as true art is kept safe in the strong hands of Auerbach.

And this is where it started. The paintings in London Building Sites 1952-62 at the Courtauld Gallery are very early works, mainly from the artist's twenties. The first work here, Summer Building Site, uncharacteristically blazing in yellow and orange, was the breakthrough, "the beginning of my life as a painter." There are ladders and uprights, but see how the paint accrues on the canvas, and acquires heft. This is where it starts.

It's true that, from now on, Auerbach gets through a lot of paint – not only the stuff that stays on the canvas, but the layers that are scraped off in pursuit of the finished work. But it's not true, and these scenes of construction amongst debris bear witness, that the paint is just being laid on. It isn't added weight. It isn't a mess. It isn't any kind of surface affectation. It is the medium from which the picture is made.

The paint is thick. It is thick so that it can be visibly pushed around. You can see how it registers pressure, strain, drag, heaves, jabs. You can feel how a structure is wrenched into existence. The painting is depicting girders, excavated gulfs in the ground, gutted walls, tips of rubble, often only vaguely recognisable. But all the time, the paint is a vector of forces.

Auerbach's painting is to be looked at, but what it depicts is predominantly not visual. "I felt there was an area of experience – the haptic, the tangible, what you feel when you touch somebody next to you in the dark – that hadn't perhaps been recorded in painting before." Haptic: relating to touch, grasp, hold.

Of course he doesn't work in a purely haptic medium. You wouldn't get much from actually running your hand over Auerbach's pictures. But you look at the paint, and see the pressure, strain etc. that his hand has imbued it with. You feel that. The picture's gestures are transmitted to your own body. That's where these Auerbachs happen.

So it's not easy for a critic to talk specifically, evocatively, about these pictures. Our response to them is most naturally expressed in gestures too. If you wanted to know about, say, Maples Demolition or Euston Steps, it wouldn't be a descriptive/analytical/poetical paragraph that did the job. It would be a strange mime or charade, involving strenuous pushing, stretching, clawing, holding firm – with some pointing, to indicate which part of the painting was meant.

This might look ridiculous to an outsider, but never mind. It would be a perfectly articulate critical discourse, more accurate than words, and capable of minute nuances. It would even allow disagreements. I thrust vigorously. You shake your head. It's not like that, it's like this. Your arms and upper body indicate a falling, a giving way.

Now there are "visual" Auerbachs in the world, pictures that you'd call beautiful, but there aren't any in this show. The colour range in each painting is narrow, and generally quite murky. The scenes are often hard to read, beyond a rudimentary sense of spaces, structures, chaos. (But then, that is what these building sites give Auerbach, a framework. There's no post-war new-world-rising-out-of-destruction optimism.) All the action is in the various ways the paint is physically shifted.

It's a dumb painting. This is why Auerbach seems so serious. His work can't be dispersed in talk. Take Francis Bacon. Of course he's a more immediately visceral painter – and much more beautiful, and much more talkable. Bacon spoke often against "illustration" in art. But his art is full of story-telling, and melodrama, and humour, and not only black humour. He's a great performer. His fan club is vocal.

Or take Howard Hodgkin, and how his work has tempted so many writers – I mean author-writers, like Susan Sontag, James Fenton, Julian Barnes, Bruce Chatwin – to expand on it. Hodgkin's art holds just the right balance between biography and abstraction. It has its sublimated stories and feelings. They're not so explicit that a writer has nothing to add, but sufficiently clear to give the writer a prompt to tease things out a little further. Hodgkin is not literary, he's just literary enough.

Auerbach gives nothing of that kind. He's remotely a realist, without being remotely literary. His work has never attracted writers. There's been some fine art criticism devoted to it, from David Sylvester, John Berger, Michael Podro, Robert Hughes (with the sad proviso that in print they haven't been able to use their arms). But for those who seek in art a springboard for their own imaginations, Auerbach has proved implacably resistant.

Powerful. Physical. Humourless. Unsensational. Untheatrical. Without a shred of cleverness or tricksiness, and without any pretentiousness or grandiloquence. But grand. But dumb. Modern art has always aspired to a kind of dumbness, to a pure visual language that needs no accessories. Auerbach takes this further, beyond the visual, to bodily states.

And more than that, to very forceful and massive states. He's a heavyweight, and if I use that ambivalent name, it's not for the thickness of his paint as such, but for the consistent heaviness of his gestures. His hand doesn't dance or caress. His "somebody next to you in the dark" would surely get shoved out of bed. Our haptic experience includes very delicate and almost imperceptible sensations, but they never appear in Auerbach's art.

So his seriousness: I admire it and resist it. The lightweights like Bacon and Hodgkin, they have variety. Auerbach (there are marvellous exceptions in his work, landscapes, heads on pillows) too much lacks play. It's as if, having discovered this seam of experience, he's had to practise it at full strength or it wouldn't be felt at all. I guess I need more play. But I agree, you might be able to show me I was wrong. I look forward to your charade.

London Building Sites 1952-62, Courtauld Gallery, London, to 17 January (www.courtauld.ac.uk; 020-7872 0220)