Philip Hensher: The simple and terrifying task of filling a space

The Tate's Turbine Hall offers a brilliant opportunity for artists to compare their own abilities

The Unilever commissions for the Turbine Hall at Tate Modern are turning out to be one of the most interesting developments in contemporary art anywhere in the world. The latest commission, from that fascinating artist Rachel Whiteread, fills the gigantic space with mountains of translucent casts of the insides of cardboard boxes. Piled up into ziggurats, they resemble cities made out of clouds, icebergs, the utmost peak of gigantic mountains. It's an ingenious and successful solution to a considerable problem.

But what is interesting about this series of commissions is that every artist has faced exactly the same problem. The space of the Turbine Hall is an intensely dramatic one. It is a simple, easily graspable shape, but - as the visitor progresses into the space - it reveals itself as so colossal that hardly any art can reasonably be expected to fill it. Each commissioned artist has had to think of a unique solution to this wonderful space; each one, as time has gone on, has found himself competing with his predecessors. There is no overt competition involved; nevertheless, this immense technical challenge has allowed us to compare the imaginative ingenuity of a succession of artists in unforgiving ways.

It has taken time for artists to understand the nature of the problem - let alone come up with satisfactory solutions - and in the meantime some very good artists have come a bit of a cropper. The commissions which haven't really worked are the ones where an artist tried to fill the space with a colossal object. Louise Bourgeois, that brilliant artist, was the first. Her structures, enormous in any other context, failed to engage with the space at all.

Another surprising failure was Anish Kapoor, who tried to articulate the entire gigantic space with a swooping, lily-like construction, stretching from one end of the hall to the other. Dramatic as it was, it somehow failed to do more than occupy the area, and it made you realise that there is no point in the colossal if you can't retreat from it and see it from an imposing distance.

After that, I think, artists have really started to come to terms with the space. Olafur Eliasson's enormous glowing sun, an artwork which seemed to say that the space was so enormous it might have its own weather system, worked by paying, above all, a compliment to the room itself. It was justifiably the most popular of the exhibits and people soon took to lying down on the floor to see themselves reflected on the mirrored ceiling.

Bruce Naumann's commission was much criticised at the time for its apparent lack of ambition, but actually it was one of the most effective in articulating the entire space. All it was was a series of loudspeakers, repeating individual snatches of speech. The hall was filled with layers of noise; the real-life hum of talking visitors, the confused babble of the combined fragments, and, as you walked past each pair, the sudden clarity of an observation, often absurd but lucid. Somehow, once the space was emptied of the physical, filled with disembodied babble, the proportions of it emerged with a most beautiful clarity.

And now the accretions and collapses of Ms Whiteread's contribution. The reason the Turbine Hall commissions are proving so fascinating is that they run directly counter to the whole tendency of art over the last 100 years or so. There's been an increasing freedom offered to visual artists, writers, and composers; what this has meant, in practice, is not that individual artists operate within a context of complete freedom, but that they evolve their own sets of rules and conventions. Which may not be the same as anyone else's.

A century and a half ago, one could have readily and unselfconsciously compared sonnets by different poets; an Italian landscape by different painters; a sonata-form concerto movement by different composers. Now, their descendants may choose to work in conventional forms, but they are unlikely to constitute the backbone of anyone's work and, in any case, it is most improbable that you would be able to compare similar formal ventures.

These days, where there is no automatically shared common formal language except a historical one, anyone trying to compare different practitioners of the same art is reduced to vague questions about how well they've been able to carry out their own intentions. I don't say that this is necessarily a bad thing; I personally wouldn't want to live in a world where every composer was still writing symphonies in B flat major with second subjects in F major. I like the looser inventiveness with which we now live.

But the Turbine Hall commissions do offer a brilliant opportunity for artists to compare their abilities when faced with exactly the same challenge. Here is an enormous space, with its own intrinsic interest. What can I do that will make an impact here; how can I give the sense that it is my imagination, not just a big thing, filling this beautiful arena?

It is a daunting commission to accept. Not just because it's an immense technical challenge, but because it does away, at a stroke, with one of the most effective defences of modern art against criticism: you can't denigrate my work, because I'm not only not doing what you think art should, but because I'm not doing what any other artist is doing. Here, the artists are doing what other artists have tried, and sometimes failed to do. It's the simplest and most frightening task imaginable; to fill a space.