René Magritte: The Pleasure Principle, Tate Liverpool, Liverpool

Surrealists loved a joke, but this A-to-Z format takes all the fun out of the Belgian artist and just makes him look arch

A is for Apple, B is for Bowler Hat, C is for Clouds; or then again, for Centaure or Collage or Curtains.

Conveniently for fans of René Magritte – and there are many of them – the catalogue to Tate Liverpool's new show of his work takes the form of a dictionary, tidying the artist into an alphabetical list. Z? That's for Zwanzeur, or "joker" in Brusseleer, Belgium's answer to Cockney.

If there is a letter other than B for Belgian that we associate with Magritte, then it is S for Surrealism. Surrealist painting has always had a problem. The whole point is that it should depict the unconscious mind – the subtitle of this show, The Pleasure Principle, comes from an essay by Freud. But painting is slow and logical. So how do you paint irrationally?

For pretty well every first-generation Surrealist, the answer was the same: to invent a repertoire of symbols, and then to move it around the canvas in endless permutations, like those games in which little plastic tiles are moved around a larger plastic tile to form a picture. This is pre-eminently true of Magritte, which is why his art lends itself so readily to indexing.

You don't have to be an art-linguist to know his alphabet: A is the apple that takes up the whole of The Listening Room; B is the bowler hats worn by the shower of little grey men in Golconda. If your Brusseleer is rusty, then the Tate's catalogue will fill the gaps from V to Z.

The aim, for Magritte, was to mix his symbols and so chance upon congruous incongruities. There are apple-plus-bowler-hat combos in this show, likewise sky-plus-brick-wall and pipe-plus-penis (a multi-layered pun, this last, the French for "blow-job" being "to play the pipe"). When we look at these unalike things, our minds conflate them: sky + brick wall = skybrickwall. And what does skybrickwall mean? Well, something to do with the imprisoning of the unconscious by the conscious, of nature by the man-made.

Magritte could have painted a sky of bricks, but he preferred to keep his elements separate, each symbol appearing on a discrete plane, receding parallel to the picture plane like scrims in a stage set: a bowler hat up front, then an apple, then a pair of breasts, then a brick wall. This separation asks your mind to make its own connections, which is why Magritte is so much more interesting an artist than Dalí, who does the connecting for you.

Now, if you find yourself yawning at this point, forgive me. Surrealists loved jokes; critics, on the other hand, have to explain them. To say "This is how a Magritte works" is like saying "Let's analyse that pun you just made". Magritte faced a problem with rationality, and so, thus, do his critics. Curators, too, suffer with Magritte, their problem being how to rationalise visually the work of a man who spent his art being visually irrational.

And that is the big flaw in this show. Critics can't really write Surrealist reviews – not if they want to stay on the pay-roll, anyway. But curators can play around with curating, and the Tate's don't. Their show is arranged thematically, separating Magritte into mini-Magrittes, one of which painted part-object nudes, one monuments, one who was political, one not, and so on. Like its catalogue, the exhibition systematises the artist and explains him. And, in the end, it makes him seem arch – a man who hit on a trick circa 1926 and went on performing it for 40 years; the facile inventor of a canny uncanny.

Even more than most painters, Magritte suffers from over-exposure. Seeing a roomful of his bowler hats is very much less useful than seeing one example. Classification calls for evidence to back it up, and, on the fourth floor at Tate Liverpool, this means many repetitions: clouds, bricks, ever more hats. Magritte may have been repetitive, but pointing it out isn't necessarily helpful.

I am no fan of wacky curating, but you can go too far the other way and this show does, which is a shame. Couldn't there have been just a hint of Surrealist jeu d'esprit? One imagines Magritte wandering around the Tate and sighing, then mooning a guard. Fewer pictures and more drama might have brought his genius to life.

That genius lies in his having been genuinely subversive – in cheekily copying his own work long before Warhol (thus two identical paintings, both called The Flavour of Tears), in combining words with monumental landscapes before Ed Ruscha was born. And, every now and then, Magritte is a deeply poetic painter: The Night Owl is a heart-stopping picture, and would be even without the little behatted man standing under a lamp post in his own front room.

To 16 Oct (0151-702 7400)

Next Week:

Nina Caplan visits the Thomas Struth show at the Whitechapel Gallery

Art Choice

Taryn Simon's unsettling show at Tate Modern, London, A Living Man Declared Dead and Other Chapters, comprises portrait photographs of the members of 18 family trees (to 6 Nov). Also in London, the Courtauld is showing the paintings and poster art of Toulouse- Lautrec, featuring the Parisian dancer Jane Avril (to 18 Sep).