I am at the City headquarters of the financial analysts Bloomberg for an "In Conversation" event with the American artist Tom Friedman, whose exhibition has just opened at the revamped South London Gallery. Peckham is a bit too far away for City types, so Friedman and his interrogator - Sarah Kent from Time Out - have decamped, PowerPoint at the ready, to the Square Mile. "It's just like the Renaissance," breathes a City banker beside me. "You know, the way Bloomberg sponsors artists." I'm not too sure about this, and I don't know

how much Michael Bloomberg wants to be equated with Lorenzo Medici, but his London base oozes confidence, from the purple plush carpets to the lift attendants. Plus, the air-con is blasting away, there is chilled sparkling water and Kent is always a star turn.

Friedman's work is challenging. The audience is attentive, but there are audible snorts of derision at the slides that show artwork involving glued-together polystyrene packing chips, sliced and reassembled Cheerio boxes, and an A4 piece of paper carefully torn into a thousand scraps and positioned around an empty shape of the same. "I call this In Memory of a Piece of Paper," says Friedman. It is almost the only work that comes with a title.

"My ideas are fleeting, and I feel I don't own the meaning of these works," he says. "Art is like a pill. Or some sort of medication. It has a discrete shape of its own, but when you consume it, it has another effect altogether on the viewer." Kent points out that Friedman is the same age as Damien Hirst, but that his work lacks the "grand gestures" of the YBAs. No stuff about dying, sex or gender roles here. Well, there is if you seek it out, but there doesn't have to be. A tiny plane flying amid fluffy clouds could mean one very political thing, but then it could mean something else entirely.

Such evasive action is tricky, particularly for arts commentators, as Kent gracefully admits. "My job is to do this . . ." she says, imitating someone scribbling. "To write and come up with suggestions about what the work might be. When I was an art school teacher and my students said 'I don't know what this means - you decide', I would be very critical of them." Friedman shrugs. "What is this creative process?" he quips, looking at a slide of one of his works, a skein of hair dangling in front of a white sheet of paper. "I call what I do 'making objects to think about'."

The South London Gallery has been rather adroit in choosing to reopen with Friedman, an artist whose work will not be categorised or easily explained. Work that has to be figured out by the viewer is always satisfying, but it seems the straightforward narrative favoured by some of our artists may have, for the moment, gone up in smoke metaphorically as well as literally. What more is there to say about Everyone I Have Ever Slept With?

Meanwhile, at Tate Modern, thousands of people are wandering around the Edward Hopper blockbuster, wondering what his lonely ladies and disgruntled-looking men in trilbies are doing, or about to do. The blank windows and empty streets don't offer any clues, either. Even the dreaded Jack Vettriano, with his arrays of tray-carrying butlers in the surf and women on sofas, is not about to come clean about what might be going on.