The dying of the light: The man referred to as 'Spain's greatest living artist' has made a serious mistake, says Andrew Graham-Dixon; plus new work in London

The reputation of an artist, once established, is not easily undermined: too many vested interests, commercial and critical, are bent on sustaining it; there have been too many exhibitions of the work; too many museums and too many private collectors have invested in it. The result is a form of creeping critical inertia, a strategic blindness to the embarrassing possibility that the artist's powers may be in decline or that his imagination may be on the wane. This does him no real favours, even if it does keep the money coming in. The danger is that he may end up believing his own publicity.

'Antoni Tapies: A Summer's Work', at Waddington Galleries, suggests that the man customarily referred to as Spain's greatest living artist has made just that mistake. At 73, Tapies has been turned into an institution in his own country. In 1990 the Fundacion Antoni Tapies, a permanent museum devoted to his work, was established in his honour in Barcelona, and during the course of his career he has been awarded an excess of those 'internationally prestigious' prizes which exist for the sole purpose, it would seem, of miring senior and already wealthy artists in their own self-importance: the Order of Art and Literature from the French Government, the Golden Lion of Venice, the Peace Prize from the United Nations for Spain. During it all, his work has subsided, gently but inexorably, into chic mediocrity.

Tapies was, once, an innovative and influential artist. The battered abstracts that he created in the 1950s and 1960s were tacit protests against the Francoist regime: pictures that evoked state brutality in their scarred and pockmarked and graffiti-ised surfaces, recalling executions and gunfire on city streets. But Tapies has increasingly become a mannerist of his own youthful devices. He has turned out to be an artist who, however venerated and however influential - his work may be detected behind that of many other European artists with a fondness for the pathos of distressed surfaces and poor materials, ranging from Joseph Beuys to the Italian exponents of Arte Povera - has found himself unable to move on and to develop with age. His work has become not richer and deeper but increasingly shallow and rhetorical.

'Tapies: A Summer's Work' is full of works of art which strain for a single and predictable effect of poignancy. Huge panels plastered with sand are intended to evoke barren landscapes, the wastelands of an old man's morbid imagination. Scratched into them, you find assorted vanitas motifs, most notably Tapies' trademark cross, hinting at thoughts of impending death or the pain of crucifixion. And affixed to them or to each other, in various configurations of collage and assemblage, you find countless forms of memento mori: sheets of rusting steel intended to evoke entropy and decay, the inevitable tarnishing of bright youth; folded hospital blankets; open boxes like coffins, meant to signal an artist's brave confrontation with his own mortality.

The sympathetic eye may find pathos in such work, but, in truth, the entire exhibition smacks of opportunism. Tapies trades in easily won effects of solemnity and his late art seems to caricature rather than genuinely express the emotions great artists are conventionally expected to feel in their old age. The result is a kind of modern pastiche of the dark and deep emotions of Rembrandt's late self-portraiture. Regret, morbidity, a sad consciousness of the dying of the light: these are the feelings which, it is intimated, lie behind the weathered surfaces, the glimmering voids and pathetic detritus that make up the works of Tapies's maturity. But if there is feeling in Tapies's late work it is feeling in stage make-up. How effortless, and how easily prolific, Tapies now seems. Just one summer's work, of which the Waddington show represents only a part, currently fills five large galleries in Cork Street. Rumour has it that the Fundacio Tapies in Barcelona is planning an extension.

At the Lisson Gallery, 'Beyond Belief' offers the rather different spectacle of a group of youngish artists, undistracted by fame or fortune, refusing to take themselves too seriously. The exhibition organiser, James Roberts, defines the theme of the show in an extremely brief note as 'the representation of perceptual experience and the reading of emotion and incident where no narrative initially appears to be present'. A playful, contrived oddity and a fear or suspicion of anything too overtly resembling self-expression is just about all the assembled artists might be said to have in common.

Stephen Murphy shows family snapshots artfully altered on a graphics computer to erase the people photographed and leave only the mises-en-scene of the photograph behind: the empty patch of lawn, the blank garden wall, on which or in front of which someone once posed. A knowing exercise in banality and pseudo-sociology, this, suggesting how little you can tell about people from the anonymous everyplaces in which they choose to be photographed: a kind of anti-portraiture, an art glumly focused on an absence. Nearby, Pierre Bismuth's work for video, What, is similarly, self-consciously self-defeating. A word appears, projected on a wall, followed by its synonyms selected from a thesaurus: one of these is isolated, then followed by its synonyms; and so on. How quickly, you note, the thesaurus takes you away from the original meaning of the original word, how fast you get from 'united' to 'elegant'. The infinite corruptibility of language would appear to be Bismuth's theme.

Small conceptual exercises, whispers of discontent: Jane and Louise Wilson, identical twins, show a video of themselves being hypnotised, once in English, once in Portuguese. Each time they seem to enter the suggested trance. Did they really? Does this mean hypnosis works through intonation alone? Does anyone care? Philippe Ramette, oblivious to the arcane concerns of the Wilson twins, concentrates on his own and produces a serio-comic emblem of frustration and suicidal intent. Its title is Objet pour Se Faire Foudroyer, which may be roughly translated as 'machine for getting struck by lightning', and it consists of a metal suit with a lightning conductor for a hat. If 'Beyond Belief' says anything about the spirit of art today (which perhaps it does), it suggests that the spirit of the Surrealists and the Dadaists is still alive, if muted. Whether this is a good thing or a bad thing is open to debate.

Sarah Lucas, who is showing at the Anthony D'Offay Gallery, is herself a sort of Dadaist: 'an aesthetic terrorist pillaging mainstream culture', as the critic Sarah Kent generously put it on the occasion of her last exhibition at the Saatchi Gallery. At the Saatchi Gallery, she showed silkscreened blow-ups of misogynistic double spreads featured in the Sunday Sport. At Anthony D'Offay, she exhibits a series of close-up photographs of a naked man playing with a beercan as if it were his penis: a sort of narrative, which climaxes in a spray of white froth as the ring is pulled on the phallic can. It is not easy to know what to make of this. It may be meant as a straight-faced deconstruction of the phallocentric male fixation on beer and beer-drinking, in which case it is very silly indeed. Or it may be meant as a parody of that kind of earnestness, a piss-take of a certain kind of politically correct art, in which case it is just a bit silly. Either way, I bet she doesn't drink Carling Black Label.

(Photograph omitted)