Beuys's Hirschdenkmal fur George Maciunas (Stag Monument for George Maciunas) is an encapsulation of everything the artist represents. It was Beuys's aim to transform fundamentally the way we see and think. The only way to do so was "to revolutionise human thought. First of all revolution takes place within man. When man is really a free, creative being who can produce something new and original, he can revolutionise time."
It is Beuys, rather than the often-cited Marcel Duchamp, who should be seen as the godfather of late 20th-century art. Both are commonly accused of fakery, but Beuys was deeply sincere - an artist with a profound spiritual basis. Where Duchamp is knowingly subversive, Beuys approaches art with reverence. In 1965, when Pop art was at its height, Beuys scrawled on a blackboard "The silence of Marcel Duchamp is overrated". If Duchamp had destroyed art, Beuys sought to revive it through personal mysticism. His every action became part of his oeuvre. Famously, he introduced into his work elements of the fat and felt that had been used to save his life when shot down during the Second World War. Beuys reinvented himself as the artist-shaman - the personification of the healing powers of art.
Inevitably, however, we have a problem with this. The problem is simply that we do not understand. Beuys's language is, necessarily, not universal but deeply personal and a certain amount of explanation is necessary. In Beuys's complex vocabulary, the piano is a visual metaphor for a stag. "The stag," he wrote, "appears in times of distress." It was largely through his use of such ancient mythic symbolism that Beuys reclaimed the German Romantic tradition which had been usurped and perverted by the Nazis.
On a more formal level, Beuys's piano sets up a tension. The wedge under the truncated third leg - a block of copper, felt and fat - suggests that the piano is about to roll away. It thus becomes a metaphor for the tenuousness of human life - the literal lack of stability that makes the human condition so interesting. Both interpretations illustrate how Beuys removed art from the political arena and gave it back to mankind.
Perhaps, though, it is in his other major work on view at Anthony d'Offay that we can detect Beuys's personal ethos. The Garbo Cycle is a series of photographs of the actress, charting her life from early stardom to old age. For Beuys, Greta Garbo was the ultimate actress - the female counterpart of the male shaman. Her photographs are surrounded and in part overpainted with Braun-kreuz - the brown pigment of Beuys's own, accidental invention - which was, as he saw it, charged with an immense power. It is a muddy, red brown colour, close to that of dried blood and reminiscent too of the brown shirts of the Nazi stormtroopers.
Once again the complexity of Beuys's work is evident. He is forever challenging us to interpret and it is in this very questioning that he succeeds. If we only take the trouble to try to understand Beuys's iconography - allow it perhaps the same time and consideration that we would that of a Renaissance altar piece - we will uncover not only his message, but possibilities for art in the coming century.
n Joseph Beuys exhibition is at Anthony d'Offay Gallery, London W1 (0171- 499 4100), to 20 Apr