Phyllida Barlow Sculpture

Sculpture's lost in the third dimension

Sculpture used to mean statues and bronzes. Now it's anything from abstract flamingoes to buddhas wearing buns, as three new shows demonstrate

There's a colour you get when you mash together all the strands in a pack of Plasticine, a sort of brown-purple with pink and white flecks. I thought you had to be five to come up with that colour, but Phyllida Barlow, in her 60s, has created it in some of her recent sculptures, now showing at the Serpentine Gallery in London. From a distance, these Wall Blobs, as they are titled, really do resemble vast lumps of Plasticine. Look closer, and they are more like organic sacs of skin packed with egg-like bulges. But they never become neat, or easy to interpret, or lose their benign chaos. Rarely has an artist so gleefully invited the adjective "lumpen".

In the Serpentine's exhibition, Barlow's boxes, ramps, cages and towers, all of them messy and paint-spattered, push up against the far purer, elegantly abstract constructions of Berlin-based artist Nairy Baghramian. Tall wisps of curvaceous painted metal have gathered like a parliament of birds - is that a pink flamingo? - in front of the windows. Where Barlow favours goo and splatter, Baghramian uses polished metal, smooth plastic, pale, precise colours. Yet she, too, is theatrical, a funster: last weekend some of her work had to be closed off because someone had interacted too enthusiastically with it, knocking over one of those abstract birds. Reflective walls of metal, balanced on what looks like soft, semi-liquid polymer stuff, block doorways and seem to invite climbing.

This is a curious idea for an exhibition - a pairing of artists who are neither collaborators nor rivals, but who kind of know one another. Barlow and Baghramian are of different generations - Baghramian is in her 30s, while Barlow began her career in the 1960s - and of manifestly different outlooks: one sleek and disciplined, the other baggy and wild. Apparently, Baghramian wrote an article about Barlow in an art magazine once. OK. And their surnames start with B. Let's get them together! And yet, challenged to work in parallel, they have risen to the occasion with confidence and a sense of fun. Barlow, in particular, evidently relishes the opportunity: her work spills out from her side of the gallery, not so much aggressively as virally.

The sculptors in Power and Beauty at the Wallace Collection would not have understood two artists working so happily side by side. The first masterpiece in this potent display of 16th and 17th-century bronze statuettes from the collection of architect Peter Marino is a vicious image of Samson slaying the Philistine. As the biblical giant raises his mighty club to smash it down on his enemy, his face is a hate-filled mask. This is believed to be a work by Baccio Bandinelli, a 16th-century Florentine sculptor. To emphasise the masculine intensity of the violent world depicted in the sculptures here, the sword of Cosimo I de' Medici, so beautiful it would almost be an honour to be struck with it, is also on display.

These exhibitions are worlds apart. At the Serpentine you have blobs; at the Wallace, highly wrought life-like figures. They are as hard to reconcile as, say, Tory and Liberal Democrat politics. But they are connected by a word: sculpture. The Serpentine show is explicitly about sculpture - it presents, says the gallery, "two positions on sculpture in the 21st century". When it comes to Renaissance statuettes, we don't need to be told. A bronze of fighting nudes is framed by tradition.

But look at these two exhibitions together and you have an interesting question: if both are sculpture, what does that word mean? How can a wooden ramp, an abstract flamingo and a bronze goddess all be sculpture? It is a modern cliche that painters have no place in a photographic age. But in reality, painting always seems to seduce every generation one way or another - it never quite goes away. But what has gone away is any traditional idea of sculpture. In 1600, sculpture meant statues; it meant statues when Rodin was creating his disarming figures in the 19th century, too. Today, the link between statuary and modern art seems utterly gone. It is easy to see how a photographic artist draws on the history of painting; it is less easy to see how a maker of installation art has anything to do with the history of sculpture before 1900.

At London's Whitechapel Gallery, the rooms are filled with a clutter made up of everything from pedestals borrowed from museums, to video footage, to a wall of boxes and a haystack. Is Rachel Harrison's The Conquest of the Useless an exhibition of sculpture? It is three-dimensional and uses sculptural pedestals - but somehow it does not seem apposite or helpful to call it sculpture. This is art in general, a comment on today's world, a satire on excess, a groovy collection of dross and waste. Profound it may be, but sculpture it ain't.

So what makes Barlow and Baghramian sculptors? What distinguishes them from Harrison's kind of contemporary art and connects them with the Renaissance bronzes? It's a question of emphasis. Just as we call something painterly if it wallows in the wetness of paint, so it makes sense to call a work of art sculptural when it draws attention to its occupation of space. If you find yourself enjoying or being repulsed by what an artwork is made of and how it's been made, by its sensual presence, then hey - you are looking at sculpture. In the 20th century, as artists drew systematically on Marcel Duchamp's idea of the readymade, it became fashionable to describe their work as "objects"; the old term sculpture did not seem to apply. This is still true of a vast amount of art being made now. A Damien Hirst vitrine is an object; a Richard Serra wall of steel is a sculpture. An object is transparent. A sculpture is opaque.

In spite of the death of the statue, sculpture remains an alive and productive tradition. To make a statue now is to do something consciously kitsch - just look at Marc Quinn's latest excursion into pseudo-figurative sensationalism - but there are more creative ways to engage with tradition. I can't help thinking Barlow must have visited the Victoria & Albert museum when she was creating her new works. One of her creations is called Balcony - a wooden box mounted on the wall, with blue flaps of colour. For me, it evokes the Renaissance balconies and tombs recently plastered into the walls of the V&A, sharing their sense of sculpture as something pictorial and architectural. Sculpture is something that can be as big as architecture, and yet is useless: it is a house you cannot live in, or, as in the conical spires at the heart of Barlow's show - one standing, one fallen - a tower you cannot climb, a tunnel you cannot crawl through.

Of the three contemporary sculptors (or object makers, or plain artists if you prefer), I like Barlow the best by far. She wins the Serpentine standoff (for surely she and Baghramian are rivals in the end) through sloppy resilience. There's a congested, matted reality to her art that stays in your mind. Baghramian's smooth shapes slip down more stylishly, but slip from memory just as easily. Perhaps this is the other thing that makes a work of art qualify as sculpture: it endures. The bronze statuettes at the Wallace look as fresh now as when they were made, and will do in another 500 years' time. Barlow's works might seem to be the opposite. They are designed to be recycled. They have no physical staying power. But they lodge in your brain; they are cussed. A mess makes itself felt, and a memory can be as good as a monument.

Nairy Baghramian and Phyllida Barlow are at the Serpentine Gallery, London W2 (020-7402 6075), until 13 June. Beauty and Power is at the Wallace Collection, London W1 (020-7563 9500), until 25 July. Rachel Harrison is at the Whitechapel Art Gallery, London E1 (020-7522 7888), until 20 June.