When you decide a work of art is bad -- as most of them are bound to be -- you often know just what it is that you dislike. For those works that please -- not quite so many of them -- you can also mostly check off the sources of your pleasure. But when it comes to that tiny fraction of all art that seems really excellent, the reasons are much harder to pin down. Read any five experts on Michelangelo, and you'll get five takes on what his greatness is about. Maybe subtlety, even density, is crucial to artistic excellence.

If that's the case, then the art of Rodney Graham, a 56-year-old Vancouver artist whose career has flourished in Europe, has a bright future. A touring retrospective of his work, titled "A Little Thought," recently touched down at the Institute of Contemporary Art in Philadelphia, after stops at the Art Gallery of Ontario in Toronto, the prestigious Los Angeles Museum of Contemporary Art and the Vancouver Art Gallery. (Those three venues organized the show.)

The exhibition provides a wide range of very different and peculiar pleasures. It's just hard to say precisely where your enjoyment comes from as you're having it, or even after the fact.

Maybe part of the pleasure comes from the variety itself. Most artists have a trademark style or shtick that they hit on when they're young, then hang on to across the length of their careers. In Graham's show, however, you're never sure what's likely to come next.

One 1996 installation consists of a peculiar little shack made of rough lumber. Inside, you watch a black-and-white film loop that's three minutes long. It starts off showing a spiral of tiny sparks, like the stars in a far-off galaxy. Then, as the loop continues, a spiral of dull light starts to glow behind those sparks, then shines bright and finally begins to fade again until only the shooting "stars" are left, at which point the whole process begins once more.

A glance at the title -- "Coruscating Cinnamon Granules" -- and a few more run-throughs of the loop, and you realize what you've been looking at: It's the spiral element of an old-fashioned electric stove. First it heats up enough to turn a sprinkling of spice into a galaxy of flying sparks, then starts to give off light as well as heat, then fades away again once it's turned off. Cosmic sublimity has been simulated using the most basic means. But even though Graham takes care to leave those means absolutely bare and evident, somehow the sublimity doesn't fully disappear.

Not far away in the show, there's a display of printed and book works that have an absolutely different feel. One object is part of a printed score whose music is built around an interlude that was added to Wagner's opera "Parsifal" for its premiere in 1882. (The stagehands needed extra time for a complex scene change.) Graham, an accomplished musician, provides instructions for manipulating and extending that original composition so that it would take almost 40 billion years to run through all its complex variations.

Back into another dark projection room, and nature is once again the subject, in a grand 1999 video projection called "Edge of a Wood." This time, all we see is the far side of a forest clearing, shot on a pitch-black night and then projected across two immense screens. The video shows some kind of bright, irregular light illuminating an almost solid wall of tossing trees and foliage, which flickers like an image by Monet. Imagine an impressionist painting done on a black ground, so that each leafy dab of paint stands out against the dark, and you'll get an idea of the effect. Except that paintings come silent, whereas Graham's piece is full of noise: The roar of a helicopter is its soundtrack, which lets us know we're watching some kind of deep-forest landing pad, visible thanks to the aircraft's spotlight or its landing floods.

Returning to the main gallery, and heading to a glass vitrine, you find a pristine copy of Ian Fleming's "Dr. No." It is unchanged by the artist, except that Graham has inserted a newly printed page -- Page 56a -- into the open book. That insert takes 007's brief encounter with a deadly centipede and extends it to excessive analytic length, until Fleming's normal narrative picks back up on Page 57. It's almost as though Marcel Proust or Henry James had made a lightning strike on Fleming's prose.

And now back to video for another piece, shot in black-and-white in 1994, that's equally but differently strange. Called "Halcion Sleep," it shows a man clad in old-fashioned striped pajamas who lies asleep across the back seat of a car as it is driven through a city late at night. The piece opens with captions that tell us that the man is Graham himself, who rented a motel room in a Vancouver suburb, took a strong dose of the sleeping medication named in his title, then had himself "kidnapped" and driven to his downtown apartment. He has staged a kind of real-world reenactment of a classic moment in film noir, but without the crutch of plot and editing to move events along. Here's noir as a real-time experience, rather than as Hollywood fakery.

Then there's "How I Became a Ramblin' Man," a work shot on gorgeous 35mm color stock, then transferred to DVD for gallery projection. It shows a classic cowboy (Graham again) with hat and fringed buckskin jacket, horse and guitar. He rides into view out of a sunset, picks his way across the fields and streams of Marlboro Country, sets hisself down for a spell to sing an achy-breaky song, then saddles up again and rides off into the hills -- ad infinitum, as the piece loops every nine minutes.

Western cliches like these become cliches through repetition, but this piece repeats them to the point where they can resonate again. You almost start to feel for the figure on screen: He's so thoroughly fenced in by formulas that his classic cowboy gloom seems to make sense.

The show also includes a placid film of Graham cycling through an urban park after taking LSD. And a lavishly shot color loop of Graham, costumed as a pirate, lying unconscious on a desert-island beach, waking up, shaking a nearby palm tree for its coconuts, getting hit on the head by one, falling unconscious on the beach, waking up, shaking a palm tree . . . and so on and so forth.

You can spot threads that might tie all this work together -- so many threads, in fact, that it's hard to tie Graham down to any single one.

One obvious theme might be humanity's strangely artificial place in nature. In Graham's work, man seems neither part of nature nor apart from it, but in dangerous tension with it.

Another, more interesting reading might see the work as somehow about the failure of some of our most cherished notions about art.

As I've suggested, the view of the natural sublime, once said to be central to art, pans out in Graham to be an overheated kitchen element, or the product of a noisy, even predatory, flying machine.

Or there's the old cliche that art is supposed to let us in on the unconscious. Graham tests that idea in his two works where he takes drugs, and then shows that he looks pretty much the same as anyone who's stone-cold sober. In life and art, what you see is what you get; anything else takes place deep in our unviewable insides.

Even the artistic expression of heartfelt emotion, whether in Wagner, Fleming or honky-tonk, seems to get questioned in Graham's work. It all seems to be about a set of formulas that artists manipulate at will. Graham stretches Wagnerian pomp almost to infinity, puts Fleming's moment of terror on pause and makes countrified angst repeat itself until there's almost no believable emotion left in it.

And yet -- there are always dozens of "and yets" in any reading of Graham -- there's a funny sense that Graham believes that formulas can work. Part of his practice as an artist has involved writing and singing relatively straight pop songs, which he issues as CDs or uses in soundtracks for his projections. (The country tune we hear in "Ramblin' Man" is by him, as is the stoner soundtrack to his acid trip.) Graham understands that good pop music is more about the bravura manipulation of cliches and formulas than about truly novel takes on human life. And that, so long as we acknowledge this manipulation, good work can come out of it, as well as a huge range of interesting pleasures.

Ditto in art.

Deftly manipulating artistic formulas: A still from "Vexation Island," part of "Rodney Graham: A Little Thought."Tweaking classic notions of cowboy gloom: "How I Became a Ramblin' Man."