The newspaper stand outside Tate Britain announced "50,000 estate agents to lose jobs". My immediate thought was: imagine the loss to the nation of all that euphemism. In this age of transferable skills, in what other field could you employ a gift for making the pinched and poky "cosy" and "charming", or for selling the gutted and derelict as space with "scope for an imaginative buyer"? How else could you utilise the ability to keep a straight face while describing a flat on a flight path as "convenient for the airport"? Then, as I entered the gallery, one possible opening for the legion unemployed property consultants immediately became apparent: writing catalogues for the nation's emerging conceptual artists. Those flogging the merits of the Turner Prize hopefuls, as ever, set the standard.

In recent years the emperor's new prize has thrown up some inspired hyperbole, but in advance of the winner being announced, this year's crop of blurbs has already raised the bar. Given that the visual merit of the work of the four contenders for the prize itself may not have been immediately apparent, particularly not to the casual viewer fresh from the Francis Bacon retrospective upstairs, the short introductions printed on the gallery walls have become essential reading. It is here that the real art lies.

Each description has its surreal merits. It would be easy to imagine that the Polish wannabe curator Goshka Macuga simply chose two artists from the Tate's archive and cut and pasted their work together in moderately surprising collages. The two artists she has chosen are the sometime lovers Paul Nash and Eileen Agar, which gives the work a vague romance (she does the same trick with Mies van der Rohe and his partner Lilly Reich, too, in a more sculptural way). But to appraise the display in this way would be to miss what is really going on here, and enlightenment dawns only after consultation with the blurbist's introduction. In this light, Macuga's "interpretation of these relationships shapes a countercultural theme in the history of modernism based on spiritual affinities, intimacy and intuitive understandings". In other words, she puts one thing next to another - a swooning beauty on a bomb site, a shadowy figure on a pathway - and plays modest games with the results.

In the adjacent room, changing the tone abruptly, Cathy Wilkes exhibits a pair of unmanned supermarket checkout conveyor belts. Next to one is a naked mannequin on a lavatory, adorned with wedding horseshoes and rose-petal confetti. Next to the other is an identical dummy, slumped and draped with dirty towels beside an empty baby buggy. The belts are lined with unwashed cereal bowls; there is a disconnected cooker, a stash of empty Bonne Maman jam jars, various spent batteries and piles of roof tiles. It is not essential to have a GCSE in sociology to deduce that this is a clunky allegory of the more dubious charms of domesticity.

Read the small print, however, and you find that what you are in the presence of is something rather more significant. "Wilkes's installations apprehend an end point in our understanding of things as they are - a point at which words become insufficient and the naming of objects is disconnected from our experience of them" (that is to say, "I can't think of any way of describing this"). And that is not all. "These precisely placed constellations of ready mades, sculptures, found objects and manipulated images form an uncompromising questioning of the self, and a constant desire to move beyond what is known."

That particular constant desire is also what takes you as swiftly as possible to the next room to view the three films that the Bangladeshi-born artist Runa Islam has made as her entry for the £25,000 top prize. At first glance these films are likeable enough. In one, a cruel-looking woman toys with china cups before tipping them off a table and watching them smash on the floor. It's the kind of thing that Bruce Nauman was doing much better 40 years ago. In another, Islam goes to her local park with a hand-held camera; not quite in focus, it dwells first on blowing leaves, then on a gang of lazing tuk-tuk drivers; there is a bit of contrived fretting about where to look next. The third shows an artist's workshop from the vantage of a roving automatic camera, a robotic tracking shot of shelves, machinery and tools. The smashing of crockery has its moments. The park lacks a spark. The studio never makes up for what it lacks in plot with what it begins to say about the voyeurism of a surveillance camera.

The discerning buyer, however, is once again invited to view these films in more of a Foxtons-inspired context. The woman who should be more careful with her tea service in reality offers a "moment of seduction in which the viewer's agency is relinquished to the camera in exchange for its eye and memory, its prosthetic enhancement of the nature of perception". That is to say: it's a film. The "rigorously minimal" park video "gently probes the resistant layers of unconstructed reality" (that is to say: it wanders about a bit and wonders whether or not it is intrusive to film strangers), while the workshop tracking shot is all about illuminating "the darker questions of cultural self-perception by the technologies of its representation". Well, you might say, sort of.

To some extent, all of these descriptive efforts seem mere throat-clearing, however, before the claims made for the sometimes beguiling efforts of the Liverpudlian Mark Leckey. In the past, Leckey has demonstrated a quietly comic gift for picking over unlikely bits of modern culture. Which is to say, apparently, that he "has a continuing fascination with the tension that exists between image and self in the contemporary world . . . Often using found images, footage and sound, Leckey's work engages in a dynamic questioning of the connections between surface and dimension, appearance and self-determination, location and presence." Either that, or, as in this instance, he is interested in how Garfield the cat comes to life as a cartoon.

It's not only Garfield that captures his attention. While Leckey may use "his own identity as a filter for a wide variety of found material", you could also claim that he has cobbled together a few basic ideas about animation and painted shoes and filmed an incoherent lecture about them in front of a half-attentive audience. There are a couple of genuinely arresting moments in this (the reflection of the artist's own studio on the back of the head of one of Jeff Koons's high-gloss steel rabbits is one), and by this stage of the show you are clinging to small mercies. The bumbling lecture might even seem charming or cosy, were it not for the claims made on its behalf. Leckey's "ongoing practice focuses on how we might - as individuals - reclaim ideas, imagine alternative states of being and create new subversive spaces within our broader culture".

Always beware subversive spaces, particularly if they come complete with bijou gardens, compact kitchens and pseuds' corners. Whoever wins it this year - Leckey probably comes closest to deserving it - the Turner Prize can surely do better than this. Internal viewing, for once, is not highly recommended.

The winner of the 2008 Turner Prize will be announced on 1 December

Tim Adams is art critic of the New Statesman