Arguments over space

Modern British Sculpture

Royal Academy of Arts, London

Until 7 April

What is a sculpture? How will we know one when we see it or bump into it or trip over it? Things called sculptures used to be put on a plinth or a pedestal. We looked up at them, awed. Then someone removed the plinth and the things called sculptures stood on the ground, baseless.

What kind of things? Once upon a time - there is a fabulous once-upon-a-time room at the Modern British Sculpture show at the Royal Academy of Arts, filled with sources of inspiration from the British Museum - they were gods and monsters, creatures and spirits. The truly wondrous things are Baboon Wearing a "Feathered" Hood Carved in Low Relief (Egypt, c.1350BC); Forepart of a Running Leopard (Halicarnassus, c.350BC), much admired by Henry Moore; Statue of Moai Hava (Easter Island, c.1000), "Donated by the Lords of the Admiralty"; and Gudea, King of Lagash (Mesopotamia, c.2130BC), serene and splendid in mottled green dolerite.

The show also contains some invitations declined. Carl Andre's Equivalent series - better known as "The Bricks" - consisted of 120 bricks arranged in different combinations, neat and tidy as any builder's merchant. Equivalent VIII (1966) was bought by the Tate in 1972; the bricklayer is American, but the bricks are here, as a path not taken by British artists, although the sculptor Tony Cragg made leaning towers of used bricks that clung to the wall for support, as if the worse for wear.

A year later, the Tate bought Richard Long's Circle of Sticks. Long is not short of sticks. An untitled work of 1968 installed 1,318 wooden sticks collected from the River Avon Gorge, laid out in parallel lines along the floor of the gallery. This material is gathered from his cross-country walks. Long walks. The sticks are not in the show; but there is his Chalk Line (1984), composed of 10 metres of limestone fragments.

Is found sculpture a contradiction in terms? Art has been made of found objects for a long time - maybe for ever - even before Marcel Duchamp found his urinal. But the emphasis here is on the making. Sculpture, like knowledge, is made, not found. Made out of what? Does anything go? According to Cragg, the bricks and the sticks were an exploration of different ways of making, a means of claiming or reclaiming non-art materials for art purposes. "You could walk art, spit art, piss art...".

This was nothing if not natural, ecological, biodegradable. Sculpture used to be monumental, sacral, immemorial. Perhaps the most entrancing blend of the perishable and the non-perishable in the show is Urs Fischer's Untitled (2000), a suspended still life, consisting of half an apple screwed together with half a pear, hanging from the ceiling by a nearly invisible nylon thread. Fischer uses fresh fruit (and good quality nylon filament). In an earlier version of this piece, as the apple and pear shrivelled and aged, they appeared to nestle more closely together. In one way or another, sculpture is organic.

Where is sculpture best seen? Henry Moore's ideal location for his work was out of doors, in the countryside. Anthony Caro prefers to show his indoors.

"In a small space which can become almost crowded with the presence of the sculpture, the spectator becomes more involved with it."

Modern British Sculpture tries for the Caro effect without the crowding. The curatorial watchword is "conversation". Jacob Epstein's monumental alabaster Adam (1938-39), with its stupendous sex organs, converses with Moore's smug little Snake (1924). Alfred Gilbert's Jubilee Memorial to Queen Victoria (1887) converses with three powerful men: Frederic Leighton's Athlete Struggling with a Python (1877), Charles Wheeler's Adam (1934-35) and Phillip King's Genghis Khan (1963). Barbara Hepworth's carved wood and strings converse with Naum Gabo's spheric constructions. Bernard Leach's stoneware converses with William Staite Murray's stoneware, as both converse with early Chinese stoneware.

Some of these conversations are difficult. Near the heart of the exhibition, Moore and Hepworth row about the sculptor's burden. Moore's Reclining Figure (1951) is pitted against Hepworth's Single Form (1961-62). Moore's figure was originally installed on the brand-new South Bank for the Festival of Britain. It was his first large-scale bronze in a public space. It launched his career as a public sculptor: a kind of NHS, or National Health Sculptor, as critic James Hall has called him. Henceforth, it seemed as if no grand design anywhere in the world was complete without a Reclining Figure (the Unesco headquarters in Paris, the Lincoln Center in New York).

It was a breakthrough for Moore and for a new kind of public sculpture - "modern", surely, with its parts and its voids, and its multiple perspectives; puzzling perhaps, but also reassuring; yet conventional enough in its visual language for the head and body to be instantly recognisable by curious onlookers of all ages.

Hepworth's "form" was radically different. It, too, was a breakthrough. It was in every sense a monumental sculpture, and it was in no sense a figure. Hepworth was pushing the boundaries of abstraction. The huge form is both very solid and very thin. From the front, it appears flat; from the side, it has volume. An enlarged version was installed in the United Nations Plaza in New York in 1964, as a memorial to Dag Hammarskjold, the Secretary General whose early death in an aircraft crash was a severe blow to the international community. Hepworth herself made a brief statement at the unveiling: "Throughout my work on Single Form I have kept in mind Dag Hammarskjöld's ideas of human and aesthetic ideology and have tried to perfect a symbol that would reflect the nobility of his life, and at the same time give us a motive and symbol of both continuity and solidarity for the future."

The sculptor and the statesman had forged a genuine bond. They were both searching for a new kind of spirituality in the post-war world. Hammarskjöld was a deeply civilised man and something of a visionary. He made a point of visiting Hepworth's shows whenever he could; he especially appreciated her Single Form sculptures. He owned at least two. He was also a poet. After his death, a collection of his work was published as Markings, translated by W.H. Auden (who did not know Swedish) and Leif Sjöberg (who did). It contained a poem called Single Form:

The breaking wave

And the muscle as it contracts

Obey the same law.

An austere line

Gathers the body's play of strength

In a bold balance.

Shall my soul meet

This curve, as a bend in the road,

On her way to form?

The last work in the exhibition seeks spirituality in a different register. It is an inspired choice. In John Latham's God is Great (#1b) (1991), the Bible, the Koran and the Torah are wedged together, stuck fast in a shattered pane of glass, suspended in space. The sculptor has brought us to book.

Modern British Sculpture is a tumultuous show. There is ample scope for objection. It will be said that some of it is not modern, some of it is not British, and some of it is not sculpture. But it will not be easy to decide which is which. The questions it poses about sculpture's possibilities and sculpture's place in the world are fundamental, for maker and spectator alike. For his part, Dag Hammarskjöld pondered long on Meister Eckhart: "Only the hand that erases can write the true thing."