The average man sitting on the Tube, according to Gilbert of Gilbert & George, sees nothing but breasts. Now, that may underestimate the range of interests of the average man (though it is entirely consistent with the stratagems used by mass-circulation newspapers to attract his attention). As for G&G, on the contrary, they find 'ideas blow up' in their brains - not very nice ones, some people say. But then, as they are proud to acknowledge, they are 'mad, crazy artists'.
Artists are not, perhaps, the same as you and I. They make unexpected connections. William Blake remarked that where you might see the sun as a disc, something like a guinea, he saw a host of angels crying holy, holy, holy (so obviously ideas blew up in his mind too). And artists are aware of, and interested in, different things. While the average man is preoccupied with mammary glands, house prices, the time of his next appointment or whatever, an artist may be concerned, for example, with shadows.
That is what the American painter Ellsworth Kelly pointed out to me when I asked him a few years ago where the ideas for his pictures came from. 'Look in the corner of the room,' he said, 'between the blind, the ceiling and the end of the wall. There's something interesting going on there.' And there indeed, when it was pointed out, was a miniature Ellsworth Kelly - although most of us would find it hard to detect the origins of his paintings, which look like large, simple, geometric abstractions.
John Constable, about whose work I was writing last week, famously expressed his love of 'the sound of water escaping from mill dams, willows, old rotten planks, slimy posts and brick work'. 'These scenes,' he added, 'made me a painter, and I am grateful.' Nowadays, of course, it is commonplace to be soppy about rotten riverside planks and willows.
Carpark loads of people go especially to the Stour Valley on the borders of Essex and Suffolk to see exactly the same type of slimy posts once spotted by the artist. Even larger, in fact intolerable numbers of travellers arrive at Giverny in order to share Monet's once equally recondite preoccupation with the surface of lily ponds. But in each case, the artist saw it first.
It was the contention of the late Patrick Heron that everything was first seen by artists, and only afterwards were the rest of us able to notice it. Last summer in central Italy, for example, I spent a good deal of time admiring the view from the house in which we were staying, especially when the sun was sinking beyond the wooded slopes of the hills. It's just like a Claude, I would say to myself. But would I have been so admiring if Claude hadn't seen it before me?
Conversely, when an artist first draws attention to something not previously noticed, or thought of interest, it is not uncommon to be outraged. 'Take that nasty green thing away,' a member of an early-19th-century Royal Academy hanging committee is said to have remarked on being confronted with a Constable. This man was under the impression that landscapes - or, at any rate, paintings of them - should be brown, that being the colour of a mellow Claude, covered in a nice haze of yellowed varnish.
This little story brings out the distinction between an artist and, say, a painter. A painter friend of mine carefully avoids describing himself as an artist, because he feels that the word has been extended to cover too many people with no distinguishable skill or craft. Maybe he has a point. But, conversely, there are plenty of painters around with lots of craft technique, but no freshness of vision. They simply produce pictures that look like something someone else has previously done. There's no art in that. (The best, like Constable, have both art and craft.)
It's the artists, not the craftsmen, who get into trouble. Because most of us expect to see only what we have seen before, when confronted with something new - a painting of a green field, or a loosely painted lily pond, or a sculpture made from neatly arranged bricks - we, or at least some of us, are outraged. 'I don't understand it,' some of us say, with self-satisfaction. 'The artist must be mad.'
Actually, the view that artists, and also poets, are unusual is a venerable one. Plato remarked on the divine poetic fury; to the Greeks to be 'inspired' was literally to be possessed. Vasari's Lives of the Artists contains some ripe accounts of eccentricity verging on derangement. In the Renaissance, the artist was a person born under Saturn, melancholy, supercharged with black bile, a Hamlet or a Michelangelo. It was not, therefore, suprising if, like Caravaggio, he had a savage temper and dined in his studio using an old portrait canvas as a table-cloth.
You might well conclude, considering the evident sanity of, say, Titian, Rubens or David Hockney, that this theory is a lot of venerable nonsense. But novelty of sensibility is likely to go along with unusual behaviour. The children of Arles threw things at Van Gogh as he walked through the streets. Now tourists queue up to inspect the places he painted. Stanley Spencer sometimes got similar treatment in Cookham (after I wrote a piece to celebrate the Spencer centenary in 1991, a reader sent a letter announcing with modest pride that he had heaved things at the old loony himself).
In the last few decades, odd behaviour - including some that a non-artist might consider unhinged - has been considered part of art itself, in fact performance art. Thus a little while ago Michael Landy carefully destroyed all his possessions, with great attendant publicity. But, then, artists are different, otherwise they wouldn't be artists.
Is there such a thing as a creative personality, an artistic brain chemistry? We don't yet know enough about such things to be sure. There are a few clues. Around 30 per cent of art students, I was told the other day, are dyslexic. I can well believe it. I have a file of carefully preserved letters from major artists, many of them badly spelt. One characteristic associated with dyslexia is a difficulty in ordering things in a conventional fashion - which might make it easier to order things in an unconventional way.
In any case, that's one of the useful things that artists do. We don't want, as has been suggested, everyone to be an artist. Much better for dentists, bus-drivers and plumbers to do the dull, predictable thing. But perhaps Dryden was right to observe that 'great wits are sure to madness near allied'.