Groszly exaggerated

George Grosz was born in 1893, and therefore doomed to a young manhood dominated by the First World War. He died comparatively recently, in 1959, but his significant art was made before Hitler's rise to power; the Royal Academy's new exhibition concentrates on his response to life in the Weimar Republic. "The Berlin of George Grosz" is just what its title announces, the German capital as a self-portrait. The egotistical Grosz dislikes what he sees around him, yet treats the city as his own, as if it belonged to him rather than anyone else who lived there.

He was not by nature a fair reporter. Among Berliners, we cannot doubt, were brave war veterans, decent working people, cultured bourgeois and responsible industrialists. No matter. For Grosz, the meek and the innocent did not exist. They had no place in his vision of the world because he was a provincial and obsessed by decadence. Bitterness of one sort or another is common in European art after the Kaiser's war, and no wonder. But Grosz turned bitterness into something else. No artist is quite so inspired by hatred. He treated all his subjects as enemies. Swindlers, murderers, whores, extortionists, Nazis and street louts - these make up his small universe, and he hates them so much that only the most vicious caricature will convey his message.

Because he is an extremist, Grosz's style and subject matter pervert reality with the aid of realism derived from cartoon art. Here is the clue to both his distinction and his failures. Cartoonists are either men of the people (they are seldom women) or self-appointed autocrats. Grosz was one of the latter. Frank Whitford, who has organised this exhibition and written its catalogue, is of the former party.

Whitford is not only a genial political cartoonist with decades of service to newspapers, principally the Sunday Mirror; he is also a scholar, a former Cambridge don, and our leading expert on modern German art. This unusual combination of talents makes him the ideal guide to Grosz, but I feel that Whitford's natural good humour has softened his attitude to his subject's leading characteristic.

Which is that Grosz is so dislikeable. Not only is he uningratiating, it seems that his work gets better when he is most hostile. The sharp nastiness of Grosz's style makes one look for the extremes of his disgust. When he relaxes his attack on the world Grosz's drawing is that of an illustrator rather than a caricaturist, and the results are middling. Pedestrians of 1926, for instance, shows people in a street who have to walk around a defecating dog. This gives some edge, but in most ways the sheet is a German equivalent of contemporary drawings in Punch. Ironically, the drawing was bought by the mine-owner Hugo Stinnes, a frequent target of Grosz's attacks. The artist was disappointed that he had failed to wound this plutocrat and political foe.

Grosz also lamented that his caricatures of the Nazis might inadvertently have given their party some popularity. This sounds unlikely, but maybe his negativism was linked in some horrible, unthinking way with the movement for repressive politics. He was a communist for a while, but I cannot believe that he was a good one. A good communist must be an optimist and believe in the cause of the working class. No signs of such an attitude in Grosz. Good communist intellectuals are also preoccupied with questions about culture. Here also Grosz is lacking. There's no evidence that he had any personal cultivation or thoughtful interest in the future.

Except that he feared for his country. As Whitford points out, Grosz's Siegfried Hitler of 1922-23 is both immediate and prescient. The title refers to the would-be dictator's use of German mythology, which is further ridiculed by his sword and necklace of bears' teeth. This and two other caricatures from the same years represent Grosz's best and most substantial black-and-white art. They mock the conventions of traditional portraiture while adding a little novelty. Grosz's innovations come not from the general tradition of modern art (of little interest to him) but from the sub-culture of illustration and cartooning. There he found some freedom from academic procedures, as we see from the alternately stabbing, negligent and vehement marks made by his pen.

The pen is the satirist's instrument, and on the frequent occasions when Grosz uses a thin watercolour brush he makes that brush behave like a thinner, and metallic, tool. His techniques in black and white are remarkable. So also is his use of watercolour. A surprise of this exhibition is his delicate and sometimes sumptuous handling of washes and thin, liquid paint. I am not sure that such means go with his satire. Rogues at the Bar, for instance, cannot convey that the rogues are doing anything reprehensible. They are having a drink and a game of cards - as many people do, without upsetting the social order or exploiting the labouring classes.

In England we too often think that watercolour is our own inheritance and that it responds to our landscape. There was, however, a very strong tradition of German watercolour, not necessarily to do with landscape, and in the long run Grosz belongs to this strain in his country's heart. He may have hated his country, but he was unable to be an artist anywhere else. Grosz went to America when Hitler took over, but his American art is not memorable.

We remember him as a man under Hitler, but the more one looks at this exhibition the more paradoxical he appears. Are not the denunciations of decadence at the same time elaborate self-portraits of Grosz's own desires? And do not the watercolours of this combative artist reveal sentimentality?

Royal Academy, W1 (0171 439 7438), to 8 June

The world according to Grosz: 'Siegfried Hitler' (1922-23), above, satirises the would-be dictator's use of myth. Right: 'Rogues at the Bar' (c 1922). Opposite: 'Orgy' (1919)