Michael Glover: Of the 'greats' on display, Hepworth is the best of a bad bunch

How much great 20th century British sculpture has there really been? Surprisingly little. When painting was transforming itself almost beyond recognition in the early decades of the 20th century, sculpture seemed woefully absent, as if it didn't really know what role to play, as if it lacked confidence in its own purpose.

Eric Gill is, frankly, poor and Epstein only fitfully convincingly wild. By the 1930s there was Henry Moore, of course – but Moore, even the early works, strikes you as oddly dated and lumpen and derivative of much older things when compared with the innovations of, say, a Frenchman called Rodin, who died in 1917.

All that slightly effortful yearning after monumentality. The tasteful, clean-lined abstract work of Hepworth was the best of all – but that is not to say a great deal. The truly exciting work in Britain before the Second World War, it has to be said, had been made by emigrés who happened to be here: another Frenchman called Henri Gaudier-Brzeska, who died too soon for his own good, and a German, Kurt Schwitters, who will be represented in the Royal Academy show with a reconstruction of his Merz Barn in the courtyard. That's something to look forward to.

After the Second World War things picked up a bit. Anthony Caro, following the American example of David Smith, dragged sculpture down from the plinth, and made brightly coloured abstract works out of painted steel, but in recent years much of Caro's work has found itself queasily inhabiting an oddly unsatisfying space between figuration and abstraction.

Among recent works, the show promises to show us Hirst's 'Let's Eat Outdoors', which is a glass-enclosed picnic table covered with live flies. That sort of thing doesn't really contribute to a serious debate about the nature and role of British sculpture.

What then has been the problem with British sculpture in the 20th century? Why such timidity? Why this lack of vision? In part, it may be to do with the nature of the kind of thing that sculpture is. A successful sculpture is something seen on all sides simultaneously. It is a collective statement which exists, like architecture, to be embraced by many simultaneously.

Unlike a painting, it is not, in part at least, a private act. The Greeks knew this. The Assyrians knew this. The ancient Egyptians knew this. It requires a robust sense of nationhood to force it into being. Britain, little by little, has been losing its sense of collective purpose, its reason for being. That may be one of the reasons why its sculpture has been gurgling down the drain.