Now please pay attention everybody. I'm about to tell you what art is


What is art? Art is anything an artist calls art. An artist is someone who makes or does something she or he thinks of as art. Making pictures can be called graphic art, but it is quite likely to have nothing to do with art whatsoever. Take the pictures that hang every weekend on the railings of London's Hyde Park, hundreds of them. No art involved. A graffito on a railway bridge is more likely to be art, most probably bad art, but art just the same. Most art is bad, but you don't get the good art without the bad. Our best artists make stuff they know is bad; the difference is that they destroy it themselves. Tracey Emin didn't wait to be told to destroy the paintings that earned her an MA at the Royal College of Art. There are a few dealers around the place who would kill to get their hands on them; she has made sure they never will. That's the kind of thing real artists can be expected to do.

Art is a part of life, but in order to be art it has to create for itself a separate zone, what we might call the art space or the art time. A urinal is not an art object as long as it is carrying out its essential function. To make it art we detach it from the plumbing, tip it on its end and set it on a plinth. The beholder then has to entertain a galaxy of new and unfamiliar thoughts about the object, redefining it and herself in relation to it. The original object, which Marcel Duchamp called Fountain, signing it R Mutt, was rejected by the Society of Independent Artists at whose New York gallery it was supposed to be exhibited in 1917 because, they said, it was not art. In 2004, 500 British "art experts" selected it as "the most influential artwork of the 20th century".

Human beings have always done art. They have set aside time to carry out activities that did nothing obviously useful. They made images, transformed their bodies with painted marks, told stories, sang and danced. Nowadays, we imagine that these activities were "timeless"; it would be truer to say that they were "timeful", sometimes taking days for preparation, and days for performance. The times and the places they happened in were set aside.

For most of human history, the artist has had no duty to record what things or animals or people actually looked like. The subject of art was more often something that could not be seen, such as the energy of the monsoon, depicted in the rock art of the Australian Kimberley region as the wandjina. In that case the artist was a person apart, a senior lawman who inherited the responsibility of keeping the sacred images fresh. Before he could lay a finger on them he had to travel to the sacred site by a special route and bathe in the clean, cold water of the deep gorges. Sacred is just another name for separate.

Drawing and painting are fun, and most people like doing them, especially if they are considered good at them, but they are not art until they acquire separateness. A recognisable likeness of a celebrity will be artless, unless it acquires its own position in relation to all the other images of that celebrity and celebrity itself. Andy Warhol refined the image of Marilyn Monroe till it was almost insubstantial, a hieroglyph in place of a likeness, with neither age nor identity nor expression. It may seem the diametric opposite of the most famous portraits of history, but it isn't. The portraits that survive have outlived their subjects and taken on a life the subjects could never claim. Those pictures exist in their own versions of the wandjina/Warhol zone.

Studying art for A-level is really tough because of the inherent contradiction between being trained to reach a standard and finding out how to be spontaneous. The value the examiners demand is creativity, but creativity cannot be taught. Lady Gaga has said: "Once you learn to think about art, you can teach yourself." She might as well have said: "Once you learn to think about art, you can only learn from yourself." You can be taught to draw like somebody else, but you can only learn to draw like yourself from yourself. Supposing drawing is your kind of art, and supposing you are really serious.

The kids who get up at midnight and head out to a derelict wall to begin working on a graffito are working within a demanding tradition that requires the sequence of execution to have been worked out in detail in advance, before any mark can be made. They can make no money out of what they do. There are no prizes for them. They could go to jail. There is no truer example of the sacredness of the art enterprise than this. Discuss.