Visual Arts: L'homme a la mode State of the art edge

Fernand Leger embraced modernity, with all its machine-made, precision- cut smoothness - which is precisely what makes his art too good to believe.

The Leger retrospective at the Pompidou Centre begins big. At the entrance to the fifth floor galleries stands his giant painting from the late 1930s, Composition with Two Parrots, filled with a group of massive, buoyant human figures, and stretching four metres up, by nearly five metres across - about as big as a picture can get and still register as a contained picture. It stands there like an announcement of things to come. The promise is sustained.

This is something big. I don't mean the show itself, which is of course extensive, though not a real monster retro. Fernand Leger left behind him 45 years of pictures. There are about 120 paintings here (and many drawings). The exhibition could be bigger, and perhaps it ought to be. When I say "big", I mean the size of his aspirations and the role he claimed for his art. His subject: modernity, how we live it. His goal: a painting which takes on the world, addresses it, and makes it better. His career proceeds confidently through many changes without crises. Everything is decisive. He doesn't have problems. And the work offers a calm grandeur and an optimism that makes him, of the French modern masters, now the least conceivable.There's no doubt this show presents us with a problem of belief.

It presents also an artist who's most impressive when he's least original. Leger destroyed most of what he did in his twenties and his extant work begins in 1910 - an outrider to the Cubism of Picasso and Braque - and there's a view that Leger's best was over by the mid-1920s, when he began to consolidate. The present show seems to share it. At least, it gives a very intensive coverage to the period when Leger most nearly reached abstraction: the pictures of all-over battling bobbins made just before the First World War (in which he fought), the dynamic patchworks of blocks and discs made just after. But it's the use Leger made of these experiments, the worldly application he gave them, that makes him an artist to be reckoned with.

What Leger took from Cubism was fragmentation and flattened space. What he'd have none of was Cubism's mysteriousness, its spooky dematerialisation of substance; none too of its witty plays of shape. What he introduced was - as he termed it - "the mechanical element", the modern stuff which Cubism generally wouldn't touch.

In the pictures of the 1920s, Leger's attitude to mechanisation is calm and affirmative. Technology is taking over our lives: well and good. It's not the energised gee-whiz of Futurism, nor some nightmare vision of depersonalisation. The process is simply assumed, and a striking thing about these works is that they rarely depict anything that looks like an actual machine. Their explicit subjects are nudes, still-lives, landscapes; but their parts are all machine-made, roundly milled tubes and hubs and plates, precision cut sheets. Nor are the people in them robotic. The way they're assembled doesn't let you imagine them in action. But they are analysed down to the finger joints into their working parts.

What are these compositions trying to persuade us of? That technology has literally reshaped the world, and what it feels like to be in it - a matter of objects, functions and designs. All parts are equal now. Life is in their simultaneous co-operation and interaction. The life of these pictures is the way they make you believe that the parts, so clear and separate, the clipped solids and diagrammatic flats, exist in the same physical continuum, which is neither 3D nor 2D, and which has its own nervous system, slotting and fracturing, cleaving and bonding. Dehumanising and denaturing if you like; it's really a sort of modernised pantheism.

The procedure is without insinuation or estrangement. Leger makes everything unmistakable in a plain language, which insists that the world is complex but intelligible to all. No subjectivity in the artist; none encouraged from the viewer. What you see is what everyone sees, and Leger was (in principle) against easel painting, which he associated with individualism and elitism. He was interested in murals and spectacles and architecture - a side of his work the show deals with rather perfunctorily. It does include his silent film of 1924, Mechanical Ballet, though its slicing and splicing life into abstract repetitive sequences sends a rather oppressive massage which the paintings precisely don't.

In the 1930s Leger's world becomes overtly more humanistic. In scenes like Adam and Eve and the Composition with Two Parrots, human bodies dominate, no longer divided into plate-sections, but with their organic integrity restored. They're huge figures, outlined in continuous slow curves, which give them the resilience of cartoon characters. They're not characters, though. They have no psychology. The faces remain what they were before, expressionless and almost identical, the blank, schematic features of a late-Roman colossus - or, indeed, of the Statue of Liberty. They are the type of humanity.

How do they live? Though they're evidently substantial, and you can half imagine them animated, it's difficult to say what their substance and action would be. They're not fatties: there's no suggestion of flesh. But are they hard or bouncy? Are they heavy or weightless? Both at the same time. The flowing outlined shapes with their lack of jointing, the arms that bend in a steady U, make them look like inflatables, pumped up to their finger tips. The way they're modelled in light and shade gives them a surface of weathered stone. They stand immovably, and they lightly float.

They're idealisations, and the ideal they stand for is the world made safe, without being made too fun or too remotely monumental. It's a world where people work together or play together without damaging each other or exhausting themselves, and where work and play become one - hence Leger's attraction to circus acrobats. Fondness is allowed, and hugs and helpfulness, but no sex, which might introduce unmanageable tensions. It's a modernity of Marxist rather than Freudian lineage, and it takes on frankly the task of imagining what the better life would be like. Unavoidably, perhaps, it comes out as more simple than one can really believe or desire.

Simplicity is not only a way of life. It is also increasingly Leger's artistic policy: one of completely democratic openness. In the later pictures, of picnics in the country or builders high up on scaffolding, painted up till his death in 1955 (and not very prolifically represented in this show), every item has its shape and name. The bold outlines declare no idiosyncrasy on the artist's part (though they're still wobbly enough to be hand-made). The names are very general names: bicycle, tree, rope, cloud, bird, of no particular species or make. They are to be recognised as easily as a child's alphabet, things from our common world, with no expression or specifics to obstruct this recognition. They're there to say hello, for us to say hello back.

And you might wonder: don't these pictures then just say "Hello, World"? Aren't they a jolly or a bland parade of bright elements? Well, sometimes that is so. But what mostly saves them is the tense sturdiness of their construction. What ought to be light or shallow is invested with enormous gravity and grandeur. You look at this late Leger world, and everywhere you can put your finger in a picture it is absolutely without depth. But, ensemble, they are immensely serious. And I'm not quite sure what we're being asked to believe. Can we take them as seriously as they make and take themselves?

Leger seems to be seeking a public that is yet to come. That is: to receive these pictures with the easy directness and the conviction that they propose, you have to project yourself to a state where a lot of things have been sorted out, where life in the world is good enough and great enough for everyone, and these paintings are around as an affirmative reminder - not even, perhaps, really needed, because they say what everybody knows anyway. So Leger represents the future, not by depicting it but by addressing it. You can turn away from this work, certainly. But you can't see round it, because it's always ahead of us.

Fernand Leger at the Centre Georges Pompidou, Paris to 29 September (00 331 4478 1233)