Late in the day and by accident – I'd forgotten it was there – I have just seen Martin Creed's Work No 850. Walking through Tate Britain's Duveen Galleries, I heard the sound of running feet behind me and, being a south Londoner, waited for a blow to the head. Creed's sprinter – one of four on a 30-minute shift – shot past, compact, beautiful, intent. He pounded on, growing smaller, and disappeared through a door at the end of the gallery. Ninety seconds and three sprinters later, he was back again, as self-absorbed as before; and then again, and again.
It was one of the most wonderful things I have seen in the gallery. The Duveen is an intentionally monumental space, designed to hold big art with big ideas: Greek heroes and athletes, discoboli and charioteers. Here, alive and oddly fragile, was the real thing. Abreast, Creed's sprinters seem statuesque, but as they race down the gallery they fade against the Duveen's marbled massiveness. Built into Work No 850 is a sense that one day the runners will no longer be there. But, for the time being, back they come.
This tied in nicely with my reason for being at the Tate, which was the gallery's latest Art Now show, called The Way In Which It Landed and curated by Ryan Gander. Gander is a master of the accident, his most recent having been provided courtesy of the Tate. Like most art museums, the gallery can show only a fraction of its collection at any time. The rest is held at the Tate Store in Southwark, a fabled place to which Gander was given entry.
What interested him was the haphazard way in which the store's contents are hung on screens, a Steven Pippin photo portrait of 1987 below Gwen John's Young Woman Holding a Black Cat; a still life with mushrooms by Sir William Nicholson over a Fifties Richard Hamilton abstract. Gander has made two copies of these screens for one wall of his one-room show, the others being hung with the work of contemporaries he admires.
It's hard to know what to make of Gander's meta-work, and that is its intention. The material he provides is reassuringly familiar, being mostly figurative paintings in academic frames. What else would you expect in an art gallery? And yet Gander's hang, bereft of school or country, theme, era or palette, is disturbingly unreadable.
The point of all this, I'd guess, is to show that art needs mediating. Treat it like wallpaper and that is what it becomes. Standing in front of Gander's replicated Tate Store screens, you feel your brain scrabbling for a way to look – trying to make implausible connections between Stanley Spencer's Terry's Lane, Cookham and François Morellet's Two Warps and Wefts of Short Lines 0° 90°. (Don't bother: there aren't any.)
The lesson we learn is that art is not prime but contingent – that where and how and in what order we see artworks shape what we make of them. If art is handled as if it doesn't matter, then it doesn't. This vaguely melancholic theme is continued into the present with Aurélien Froment's Théâtre de Poche (2007), a video in which a young man arranges postcards on the glass wall. The cards are of artefacts – Egyptian mummies, Bohemian glass, Carl Andre bricks – and, like Gander's Tate Store screens, they are apparently stuck on any old how.
Froment's short film is about haphazardry, and its inclusion in The Way In Which It Landed feels haphazard. Without quite knowing how, you sense Gander pulling the rug out from under your feet: the present and past elide, artistic certainties swept away. In the background is the poignant sense that all art – Froment, Gander, this very work – will one day end up in the Tate Store. The only hope is that it will be rescued by a future conceptualist; that its disappearance, like that of Creed's sprinters, is only temporary.
Tate Britain, London SW1 (020-7887 8888), to 26 Oct