Riley, Bridget : Deny II (1967)

A strange fear, to dread that the supply of tunes would simply, and quite soon, run out, as all the good permutations of notes got used. Mill's anxiety seems to be the mirror image of Jorge Luis Borges's fantasy in 'The Library of Babel'. Every book there is the same length, but it's a gigantic library, because 'its bookshelves contain all possible combinations of the 22 orthographic symbols (a number that, though unimaginably vast, is not infinite) " that is, all that is able to be expressed, in every language'. The implication is that, just by doing all the alphabetical permutations, you could automatically generate masses of new books, new thoughts, new poems, and every possible rewrite " along with absolutely overwhelming quantities of gobbledegook, of course.

Both prospects are alarming. Mill sees the musical repertoire as facing imminent exhaustion. Borges imagines the verbal repertoire as being hugely extendable (though here, too, the combinations that make sense will be finite). And what's troubling, in each case, is not that the stock of conceivable tunes or books is either limited " or almost unlimited. The real worry is in the thought that every tune and every book is only a matter of permutation. It can be produced simply by going through all possible sequences of notes or letters. It's not a living creation, it's just one result among millions.

Any art that conspicuously uses permutation can prompt a suspicion of deadness. This may be misplaced, though. Bridget Riley's Deny II is a permutation picture. It seems to operate by a set of numbered instructions. You have a square field of dark grey, and it's a uniform dark grey, though the eye never feels sure about this. On this field, a grid of small ovals is laid out, 19 x 19. Each oval is the same shape, and each one stands out against the dark grey field, even where the picture is at its darkest (it is possible that this may not be visible in the reproduction).

Among the 361 ovals, there are sequential variations in both their angle and their tone. Down each column, the ovals turn through a full rotation. Along each row, they do a half- rotation, then a half-rotation back. They also go through gradations of greys, in symmetrical sequences, though these tonal scales would take longer to describe. But note that the upright oval in the centre carries the lightest tone, and the darkest ovals are nearly as dark as the background , but (in the original) not quite.

And, looking at this picture, and seeing how it's made up of distinct units that are put through definable transformations according to rules, you may think: this is a work whose performance you ought to be able to follow and analyse, step by step. That impression of perfect clarity is important. It's a crucial aspect of the work. It's true, too, when you focus on small areas. But take the picture whole, and your grasp starts slipping away. The permutations and their interactions move beyond reckoning.

The way the ovals rotate produces a sense of complex animation in the upper half of the picture. It's like an army band in a formation manoeuvre, or a flight of starlings, going many ways at once, revolving, swerving, peeling away. It defies any attempt to track it, step by step. Superimposed on this, there's the tonal agenda, equally elusive. It involves a kind of optical illusion. As the tone of the ovals converges with the dark background, it looks as if a V-shaped shadow has fallen across the picture, leaving a glowing chevron area above it. The effect, though achieved step by step, is so gradual that again you can't hold it in clear sight. The eye won't credit that it's only the ovals that are getting darker, and not the background, too.

Now it gets complicated. The patterns of the rotating ovals, and of dark and light, aren't co-ordinated. They're two different configurations, which happen to be carried by the same grid of ovals. But for that reason they can't help fusing. You keep trying to see them as in gear together. You feel that the way the ovals swell into brightness is at one with the way they swerve. Then the feeling goes. Then returns. The breathing life of the picture lies in this tension.

Mystery and clarity are not at odds. The clarity creates the mystery. The elusive feelings of Deny II occur because, paradoxically, its procedures are so transparent. You can see it's all done with regular oval elements in permutations. You hold on to your conviction that it must all be graspable. And you go down with the ship, so to speak.

THE ARTIST

Bridget Riley (b1931) is still famous for dazzling. Her black-and- white canvases of the early Sixties were classified as a movement, Op Art. No one believed her insistence that these rippling, shuddering, blazing monochrome patterns were not a deliberate attack on the retina, but a form of expression. Today, their emotional language seems clearer " a brittle repertoire of risk, wit, anxiety, hysteria, living on the edge. Later, the work goes into colour, becomes calmer and more contemplatable. Deny II is a turning-point, but her work always depends on clear, sharp, uniform shape units, and the way they synthesise. In all Riley, there isn't a single blur.