I do partly mean the question in an enquiring way. Is there some contemporary purpose in showing Siqueiros's work here and now? Is it, for instance, another toot for figurative painting? Surely not. Or is it perhaps a plug for art with openly political commitments? Well, Guttuso had them too, and that could be a lesson someone might want to teach contemporary British art. It's certainly a lesson that Siqueiros offers both in his art and in his life.
With Rivera and Orozco, Siqueiros was one of the tres grandes Mexican Muralists. And while each of these artists was concerned to produce a popular, public and political art for a revolutionary society, Siqueiros was the most politically active of them. He fought in the revolutionary war, was frequently at odds with the post-revolution governments, and spent a good deal of his life either in prison or in exile.
The pictures in "David Alfaro Siqueiros: Portrait of a Decade" come from the years 1930-40, the period leading up to his first major wall-works. The decade began with the artist (in his early thirties) jailed, and taking the opportunity to return to painting after several years given to work for the Communist party and the miners' union. He spent some of the Thirties away in the USA, and fighting in the Spanish War. And in 1940 he tried to assassinate Trotsky - then living in exile in Mexico.
This is the big anecdote about Siqueiros, and the incident is often treated very bullishly - partly because it seems such a marvellously active thing for an artist to do, and partly (contrarily) because the attempt was completely incompetent, a wild pistol shot through a closed door.
But at any rate, if Siqueiros had killed his man - and the ice-pick got Trotsky only a few months later - we know very well who would have been most pleased about it. That puts a less hearty complexion on the adventure, but I suppose the story is a good one - it turns round the idea that it's always politicians who victimise artists, and it reminds us not to take the politics of any political art in too abstract or visionary a way.
And as for Siqueiros's art ... I'm at a disadvantage. I've never been to Mexico and I've never seen the great murals first hand, and the murals are obviously the missing climax of this show. To go by reproductions, they look both mind-blowing in their manipulation of huge spaces with careering perspectives and trompe-l'uil effects that make the images jump off the walls - and also disgusting, like increasingly lurid Marvel Comics' apocalypses. Still, the easel paintings here aren't encouraging either. And the question Why? returns in purely rhetorical form. I mean, granted the work hasn't been much seen in Europe, and has been neglected in comparison with Diego Rivera's - but it' s pretty awful, isn't it?
Ambitious, yes. As a figurative artist, Siqueiros has bolder aspirations than Rivera, whose human forms settle into a uniform cuddliness composed, even in battle scenes, into compactly peaceable designs. Siqueiros borrows from all over the place - from all sorts of primitivist, neoclassical and dynamist tendencies in European Modern art, and from early Renaissance and native Mexican art - and hardly disguises it. He experiments with the paint surface, using spray-guns, mixed-in collage, fat-weave burlap canvasses, quick-dry enamel paint dripped and pooled, blow-torches. His painting urgently wants to communicate, to sear, to stir, to get a reaction.
It has two big modes: the bustingly strenuous and the dumbly solid. The one is used, broadly speaking, for images of struggle; the other for images of helpless and dignified misery. The imagery has dated, of course, all too recognisable fixtures of left-art, but I don't think that's the problem. It's the way a style always seems to be employed only for some anticipated effect. Take Proletarian Mother (1931) - in what I'm calling the "dumb" manner - a squatting anti-madonna clambered over by her needy children. Why does Siqueiros use these heavy, stiff, rounded limbs moulded in heavy blacks? He thinks they'll perform, he thinks they'll communicate down- pressed resilience. He's not trying to discover anything through these forms, he's not at work in the painting. It has its job. It does misery in the same way that, say, Tamara de Lempika's work does elegance.
Or take the "strenuous" ones, like Proletarian Victim (1933), a kneeling naked woman bound in ropes, shot in the head but her body still straining with arched musculature; or Down But Not Defeated (1939), a man thrown to the ground, head just rising again, his clenched fists, his torso, even his brow, bulging with resistance. Here you see clearly one of Siqueiros's favourite tricks, a lighting scheme which shifts abruptly from dark shade to livid-bright highlight, and which is all about pumping it up, yanking an image into intensity with sudden flashes which have no relation to any imaginable light conditions, but which can be and are applied anywhere that a jolt is needed.
He deploys this energising device all over, an irresistible tic - in landscapes and in portraits, and most grossly in a very close-up, wild- eyed Self-Portrait from 1939. It shows only the middle of the artist's face, tense and burnished, every feature bursting out from the carving dark in glistening orange. It might come from a physique magazine to illustrate The World's Most Perfectly Developed Nostril.
There is, in Siqueiros's art, an ever-present dialect of force, a will to power of which only the will comes through. His impact is all impact, and a near-view is never rewarded. His touch is lumpish, his lines perfunctory. In that respect, his experiments with the paint surface were no great risk. But I don't think the results are ever more than curious. Interesting messes, these gloopy, gritty, puckered and frazzled textures, techniques at proof stage - somebody else might be able to do something with them, and of course other artists have. It was an original departure, but that's all it was.
Oh dear. Siqueiros is in some accounts a "great". But it seems to me that his greatness is not a matter of achievement, rather a kind of occupational requirement, to do with the magnitude of his cause and indeed the physical magnitude of his mural work. I'm conscious there may be an inhibition of European taste in this judgement: doesn't the Mexicans' work invariably seem too explicit or excessive to us? But then, distance can distort vision the other way, too. For example, put Siqueiros against Stanley Spencer - often reckoned hopelessly provincial, but in many respects a similar artist. If there's a preference, it's only for the one's socialist revolution over the other's eroto-Christianity. And if there's a lesson from Siqueiros, it's already been thoroughly absorbed and exploited by some of those extremely rum painters who came out of Glasgow in the mid-Eighties. No, the news here isn't good, and we mostly knew it anyway
`David Alfaro Siqueiros: Portrait of a Decade' at the Whitechapel Gallery, London E1 (0171-522 7878) to 2 Nov